lodepng.c

/*
LodePNG version 20200306

Copyright (c) 2005-2020 Lode Vandevenne

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

    1. The origin of this software must not be misrepresented; you must not
    claim that you wrote the original software. If you use this software
    in a product, an acknowledgment in the product documentation would be
    appreciated but is not required.

    2. Altered source versions must be plainly marked as such, and must not be
    misrepresented as being the original software.

    3. This notice may not be removed or altered from any source
    distribution.
*/

/*
The manual and changelog are in the header file "lodepng.h"
Rename this file to lodepng.cpp to use it for C++, or to lodepng.c to use it for C.
*/

#include "lodepng.h"

#ifdef LODEPNG_COMPILE_DISK
#include <limits.h> /* LONG_MAX */
#include <stdio.h> /* file handling */
#endif /* LODEPNG_COMPILE_DISK */

#ifdef LODEPNG_COMPILE_ALLOCATORS
#include <stdlib.h> /* allocations */
#endif /* LODEPNG_COMPILE_ALLOCATORS */

#if defined(_MSC_VER) && (_MSC_VER >= 1310) /*Visual Studio: A few warning types are not desired here.*/
#pragma warning( disable : 4244 ) /*implicit conversions: not warned by gcc -Wall -Wextra and requires too much casts*/
#pragma warning( disable : 4996 ) /*VS does not like fopen, but fopen_s is not standard C so unusable here*/
#endif /*_MSC_VER */

const char* LODEPNG_VERSION_STRING = "20200306";

/*
This source file is built up in the following large parts. The code sections
with the "LODEPNG_COMPILE_" #defines divide this up further in an intermixed way.
-Tools for C and common code for PNG and Zlib
-C Code for Zlib (huffman, deflate, ...)
-C Code for PNG (file format chunks, adam7, PNG filters, color conversions, ...)
-The C++ wrapper around all of the above
*/

/* ////////////////////////////////////////////////////////////////////////// */
/* ////////////////////////////////////////////////////////////////////////// */
/* // Tools for C, and common code for PNG and Zlib.                       // */
/* ////////////////////////////////////////////////////////////////////////// */
/* ////////////////////////////////////////////////////////////////////////// */

/*The malloc, realloc and free functions defined here with "lodepng_" in front
of the name, so that you can easily change them to others related to your
platform if needed. Everything else in the code calls these. Pass
-DLODEPNG_NO_COMPILE_ALLOCATORS to the compiler, or comment out
#define LODEPNG_COMPILE_ALLOCATORS in the header, to disable the ones here and
define them in your own project's source files without needing to change
lodepng source code. Don't forget to remove "static" if you copypaste them
from here.*/

#ifdef LODEPNG_COMPILE_ALLOCATORS
static void* lodepng_malloc(size_t size) {
#ifdef LODEPNG_MAX_ALLOC
  if(size > LODEPNG_MAX_ALLOC) return 0;
#endif
  return malloc(size);
}

/* NOTE: when realloc returns NULL, it leaves the original memory untouched */
static void* lodepng_realloc(void* ptr, size_t new_size) {
#ifdef LODEPNG_MAX_ALLOC
  if(new_size > LODEPNG_MAX_ALLOC) return 0;
#endif
  return realloc(ptr, new_size);
}

static void lodepng_free(void* ptr) {
  free(ptr);
}
#else /*LODEPNG_COMPILE_ALLOCATORS*/
/* TODO: support giving additional void* payload to the custom allocators */
void* lodepng_malloc(size_t size);
void* lodepng_realloc(void* ptr, size_t new_size);
void lodepng_free(void* ptr);
#endif /*LODEPNG_COMPILE_ALLOCATORS*/

/* convince the compiler to inline a function, for use when this measurably improves performance */
/* inline is not available in C90, but use it when supported by the compiler */
#if (defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L)) || (defined(__cplusplus) && (__cplusplus >= 199711L))
#define LODEPNG_INLINE inline
#else
#define LODEPNG_INLINE /* not available */
#endif

/* restrict is not available in C90, but use it when supported by the compiler */
#if (defined(__GNUC__) && (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 1))) ||\
    (defined(_MSC_VER) && (_MSC_VER >= 1400)) || \
    (defined(__WATCOMC__) && (__WATCOMC__ >= 1250) && !defined(__cplusplus))
#define LODEPNG_RESTRICT __restrict
#else
#define LODEPNG_RESTRICT /* not available */
#endif

/* Replacements for C library functions such as memcpy and strlen, to support platforms
where a full C library is not available. The compiler can recognize them and compile
to something as fast. */

static void lodepng_memcpy(void* LODEPNG_RESTRICT dst,
                           const void* LODEPNG_RESTRICT src, size_t size) {
  size_t i;
  for(i = 0; i < size; i++) ((char*)dst)[i] = ((const char*)src)[i];
}

static void lodepng_memset(void* LODEPNG_RESTRICT dst,
                           int value, size_t num) {
  size_t i;
  for(i = 0; i < num; i++) ((char*)dst)[i] = (char)value;
}

/* does not check memory out of bounds, do not use on untrusted data */
static size_t lodepng_strlen(const char* a) {
  const char* orig = a;
  /* avoid warning about unused function in case of disabled COMPILE... macros */
  (void)(&lodepng_strlen);
  while(*a) a++;
  return (size_t)(a - orig);
}

#define LODEPNG_MAX(a, b) (((a) > (b)) ? (a) : (b))
#define LODEPNG_MIN(a, b) (((a) < (b)) ? (a) : (b))
#define LODEPNG_ABS(x) ((x) < 0 ? -(x) : (x))

#ifdef LODEPNG_COMPILE_PNG
/* Safely check if adding two integers will overflow (no undefined
behavior, compiler removing the code, etc...) and output result. */
static int lodepng_addofl(size_t a, size_t b, size_t* result) {
  *result = a + b; /* Unsigned addition is well defined and safe in C90 */
  return *result < a;
}
#endif /*LODEPNG_COMPILE_PNG*/

/*
Often in case of an error a value is assigned to a variable and then it breaks
out of a loop (to go to the cleanup phase of a function). This macro does that.
It makes the error handling code shorter and more readable.

Example: if(!uivector_resize(&lz77_encoded, datasize)) ERROR_BREAK(83);
*/
#define CERROR_BREAK(errorvar, code){\
  errorvar = code;\
  break;\
}

/*version of CERROR_BREAK that assumes the common case where the error variable is named "error"*/
#define ERROR_BREAK(code) CERROR_BREAK(error, code)

/*Set error var to the error code, and return it.*/
#define CERROR_RETURN_ERROR(errorvar, code){\
  errorvar = code;\
  return code;\
}

/*Try the code, if it returns error, also return the error.*/
#define CERROR_TRY_RETURN(call){\
  unsigned error = call;\
  if(error) return error;\
}

/*Set error var to the error code, and return from the void function.*/
#define CERROR_RETURN(errorvar, code){\
  errorvar = code;\
  return;\
}

/*
About uivector, ucvector and string:
-All of them wrap dynamic arrays or text strings in a similar way.
-LodePNG was originally written in C++. The vectors replace the std::vectors that were used in the C++ version.
-The string tools are made to avoid problems with compilers that declare things like strncat as deprecated.
-They're not used in the interface, only internally in this file as static functions.
-As with many other structs in this file, the init and cleanup functions serve as ctor and dtor.
*/

#ifdef LODEPNG_COMPILE_ZLIB
#ifdef LODEPNG_COMPILE_ENCODER
/*dynamic vector of unsigned ints*/
typedef struct uivector {
  unsigned* data;
  size_t size; /*size in number of unsigned longs*/
  size_t allocsize; /*allocated size in bytes*/
} uivector;

static void uivector_cleanup(void* p) {
  ((uivector*)p)->size = ((uivector*)p)->allocsize = 0;
  lodepng_free(((uivector*)p)->data);
  ((uivector*)p)->data = NULL;
}

/*returns 1 if success, 0 if failure ==> nothing done*/
static unsigned uivector_resize(uivector* p, size_t size) {
  size_t allocsize = size * sizeof(unsigned);
  if(allocsize > p->allocsize) {
    size_t newsize = allocsize + (p->allocsize >> 1u);
    void* data = lodepng_realloc(p->data, newsize);
    if(data) {
      p->allocsize = newsize;
      p->data = (unsigned*)data;
    }
    else return 0; /*error: not enough memory*/
  }
  p->size = size;
  return 1; /*success*/
}

static void uivector_init(uivector* p) {
  p->data = NULL;
  p->size = p->allocsize = 0;
}

/*returns 1 if success, 0 if failure ==> nothing done*/
static unsigned uivector_push_back(uivector* p, unsigned c) {
  if(!uivector_resize(p, p->size + 1)) return 0;
  p->data[p->size - 1] = c;
  return 1;
}
#endif /*LODEPNG_COMPILE_ENCODER*/
#endif /*LODEPNG_COMPILE_ZLIB*/

/* /////////////////////////////////////////////////////////////////////////// */

/*dynamic vector of unsigned chars*/
typedef struct ucvector {
  unsigned char* data;
  size_t size; /*used size*/
  size_t allocsize; /*allocated size*/
} ucvector;

/*returns 1 if success, 0 if failure ==> nothing done*/
static unsigned ucvector_resize(ucvector* p, size_t size) {
  if(size > p->allocsize) {
    size_t newsize = size + (p->allocsize >> 1u);
    void* data = lodepng_realloc(p->data, newsize);
    if(data) {
      p->allocsize = newsize;
      p->data = (unsigned char*)data;
    }
    else return 0; /*error: not enough memory*/
  }
  p->size = size;
  return 1; /*success*/
}

static ucvector ucvector_init(unsigned char* buffer, size_t size) {
  ucvector v;
  v.data = buffer;
  v.allocsize = v.size = size;
  return v;
}


/* ////////////////////////////////////////////////////////////////////////// */

#ifdef LODEPNG_COMPILE_PNG
static unsigned lodepng_read32bitInt(const unsigned char* buffer) {
  return (((unsigned)buffer[0] << 24u) | ((unsigned)buffer[1] << 16u) |
         ((unsigned)buffer[2] << 8u) | (unsigned)buffer[3]);
}
#endif /*LODEPNG_COMPILE_PNG*/

#if defined(LODEPNG_COMPILE_PNG) || defined(LODEPNG_COMPILE_ENCODER)
/*buffer must have at least 4 allocated bytes available*/
static void lodepng_set32bitInt(unsigned char* buffer, unsigned value) {
  buffer[0] = (unsigned char)((value >> 24) & 0xff);
  buffer[1] = (unsigned char)((value >> 16) & 0xff);
  buffer[2] = (unsigned char)((value >>  8) & 0xff);
  buffer[3] = (unsigned char)((value      ) & 0xff);
}
#endif /*defined(LODEPNG_COMPILE_PNG) || defined(LODEPNG_COMPILE_ENCODER)*/

/* ////////////////////////////////////////////////////////////////////////// */
/* / File IO                                                                / */
/* ////////////////////////////////////////////////////////////////////////// */

#ifdef LODEPNG_COMPILE_DISK

/* returns negative value on error. This should be pure C compatible, so no fstat. */
static long lodepng_filesize(const char* filename) {
  FILE* file;
  long size;
  file = fopen(filename, "rb");
  if(!file) return -1;

  if(fseek(file, 0, SEEK_END) != 0) {
    fclose(file);
    return -1;
  }

  size = ftell(file);
  /* It may give LONG_MAX as directory size, this is invalid for us. */
  if(size == LONG_MAX) size = -1;

  fclose(file);
  return size;
}

/* load file into buffer that already has the correct allocated size. Returns error code.*/
static unsigned lodepng_buffer_file(unsigned char* out, size_t size, const char* filename) {
  FILE* file;
  size_t readsize;
  file = fopen(filename, "rb");
  if(!file) return 78;

  readsize = fread(out, 1, size, file);
  fclose(file);

  if(readsize != size) return 78;
  return 0;
}

unsigned lodepng_load_file(unsigned char** out, size_t* outsize, const char* filename) {
  long size = lodepng_filesize(filename);
  if(size < 0) return 78;
  *outsize = (size_t)size;

  *out = (unsigned char*)lodepng_malloc((size_t)size);
  if(!(*out) && size > 0) return 83; /*the above malloc failed*/

  return lodepng_buffer_file(*out, (size_t)size, filename);
}

/*write given buffer to the file, overwriting the file, it doesn't append to it.*/
unsigned lodepng_save_file(const unsigned char* buffer, size_t buffersize, const char* filename) {
  FILE* file;
  file = fopen(filename, "wb" );
  if(!file) return 79;
  fwrite(buffer, 1, buffersize, file);
  fclose(file);
  return 0;
}

#endif /*LODEPNG_COMPILE_DISK*/

/* ////////////////////////////////////////////////////////////////////////// */
/* ////////////////////////////////////////////////////////////////////////// */
/* // End of common code and tools. Begin of Zlib related code.            // */
/* ////////////////////////////////////////////////////////////////////////// */
/* ////////////////////////////////////////////////////////////////////////// */

#ifdef LODEPNG_COMPILE_ZLIB
#ifdef LODEPNG_COMPILE_ENCODER

typedef struct {
  ucvector* data;
  unsigned char bp; /*ok to overflow, indicates bit pos inside byte*/
} LodePNGBitWriter;

static void LodePNGBitWriter_init(LodePNGBitWriter* writer, ucvector* data) {
  writer->data = data;
  writer->bp = 0;
}

/*TODO: this ignores potential out of memory errors*/
#define WRITEBIT(writer, bit){\
  /* append new byte */\
  if(((writer->bp) & 7u) == 0) {\
    if(!ucvector_resize(writer->data, writer->data->size + 1)) return;\
    writer->data->data[writer->data->size - 1] = 0;\
  }\
  (writer->data->data[writer->data->size - 1]) |= (bit << ((writer->bp) & 7u));\
  ++writer->bp;\
}

/* LSB of value is written first, and LSB of bytes is used first */
static void writeBits(LodePNGBitWriter* writer, unsigned value, size_t nbits) {
  if(nbits == 1) { /* compiler should statically compile this case if nbits == 1 */
    WRITEBIT(writer, value);
  } else {
    /* TODO: increase output size only once here rather than in each WRITEBIT */
    size_t i;
    for(i = 0; i != nbits; ++i) {
      WRITEBIT(writer, (unsigned char)((value >> i) & 1));
    }
  }
}

/* This one is to use for adding huffman symbol, the value bits are written MSB first */
static void writeBitsReversed(LodePNGBitWriter* writer, unsigned value, size_t nbits) {
  size_t i;
  for(i = 0; i != nbits; ++i) {
    /* TODO: increase output size only once here rather than in each WRITEBIT */
    WRITEBIT(writer, (unsigned char)((value >> (nbits - 1u - i)) & 1u));
  }
}
#endif /*LODEPNG_COMPILE_ENCODER*/

static unsigned reverseBits(unsigned bits, unsigned num) {
  /*TODO: implement faster lookup table based version when needed*/
  unsigned i, result = 0;
  for(i = 0; i < num; i++) result |= ((bits >> (num - i - 1u)) & 1u) << i;
  return result;
}

/* ////////////////////////////////////////////////////////////////////////// */
/* / Deflate - Huffman                                                      / */
/* ////////////////////////////////////////////////////////////////////////// */

#define FIRST_LENGTH_CODE_INDEX 257
#define LAST_LENGTH_CODE_INDEX 285
/*256 literals, the end code, some length codes, and 2 unused codes*/
#define NUM_DEFLATE_CODE_SYMBOLS 288
/*the distance codes have their own symbols, 30 used, 2 unused*/
#define NUM_DISTANCE_SYMBOLS 32
/*the code length codes. 0-15: code lengths, 16: copy previous 3-6 times, 17: 3-10 zeros, 18: 11-138 zeros*/
#define NUM_CODE_LENGTH_CODES 19

/*the base lengths represented by codes 257-285*/
static const unsigned LENGTHBASE[29]
  = {3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 35, 43, 51, 59,
     67, 83, 99, 115, 131, 163, 195, 227, 258};

/*the extra bits used by codes 257-285 (added to base length)*/
static const unsigned LENGTHEXTRA[29]
  = {0, 0, 0, 0, 0, 0, 0,  0,  1,  1,  1,  1,  2,  2,  2,  2,  3,  3,  3,  3,
      4,  4,  4,   4,   5,   5,   5,   5,   0};

/*the base backwards distances (the bits of distance codes appear after length codes and use their own huffman tree)*/
static const unsigned DISTANCEBASE[30]
  = {1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193, 257, 385, 513,
     769, 1025, 1537, 2049, 3073, 4097, 6145, 8193, 12289, 16385, 24577};

/*the extra bits of backwards distances (added to base)*/
static const unsigned DISTANCEEXTRA[30]
  = {0, 0, 0, 0, 1, 1, 2,  2,  3,  3,  4,  4,  5,  5,   6,   6,   7,   7,   8,
       8,    9,    9,   10,   10,   11,   11,   12,    12,    13,    13};

/*the order in which "code length alphabet code lengths" are stored as specified by deflate, out of this the huffman
tree of the dynamic huffman tree lengths is generated*/
static const unsigned CLCL_ORDER[NUM_CODE_LENGTH_CODES]
  = {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};

/* ////////////////////////////////////////////////////////////////////////// */

/*
Huffman tree struct, containing multiple representations of the tree
*/
typedef struct HuffmanTree {
  unsigned* codes; /*the huffman codes (bit patterns representing the symbols)*/
  unsigned* lengths; /*the lengths of the huffman codes*/
  unsigned maxbitlen; /*maximum number of bits a single code can get*/
  unsigned numcodes; /*number of symbols in the alphabet = number of codes*/
  /* for reading only */
  unsigned char* table_len; /*length of symbol from lookup table, or max length if secondary lookup needed*/
  unsigned short* table_value; /*value of symbol from lookup table, or pointer to secondary table if needed*/
} HuffmanTree;

static void HuffmanTree_init(HuffmanTree* tree) {
  tree->codes = 0;
  tree->lengths = 0;
  tree->table_len = 0;
  tree->table_value = 0;
}

static void HuffmanTree_cleanup(HuffmanTree* tree) {
  lodepng_free(tree->codes);
  lodepng_free(tree->lengths);
  lodepng_free(tree->table_len);
  lodepng_free(tree->table_value);
}

/* amount of bits for first huffman table lookup (aka root bits), see HuffmanTree_makeTable and huffmanDecodeSymbol.*/
/* values 8u and 9u work the fastest */
#define FIRSTBITS 9u

/* a symbol value too big to represent any valid symbol, to indicate reading disallowed huffman bits combination,
which is possible in case of only 0 or 1 present symbols. */
#define INVALIDSYMBOL 65535u

/* make table for huffman decoding */
static unsigned HuffmanTree_makeTable(HuffmanTree* tree) {
  static const unsigned headsize = 1u << FIRSTBITS; /*size of the first table*/
  static const unsigned mask = (1u << FIRSTBITS) /*headsize*/ - 1u;
  size_t i, numpresent, pointer, size; /*total table size*/
  unsigned* maxlens = (unsigned*)lodepng_malloc(headsize * sizeof(unsigned));
  if(!maxlens) return 83; /*alloc fail*/

  /* compute maxlens: max total bit length of symbols sharing prefix in the first table*/
  lodepng_memset(maxlens, 0, headsize * sizeof(*maxlens));
  for(i = 0; i < tree->numcodes; i++) {
    unsigned symbol = tree->codes[i];
    unsigned l = tree->lengths[i];
    unsigned index;
    if(l <= FIRSTBITS) continue; /*symbols that fit in first table don't increase secondary table size*/
    /*get the FIRSTBITS MSBs, the MSBs of the symbol are encoded first. See later comment about the reversing*/
    index = reverseBits(symbol >> (l - FIRSTBITS), FIRSTBITS);
    maxlens[index] = LODEPNG_MAX(maxlens[index], l);
  }
  /* compute total table size: size of first table plus all secondary tables for symbols longer than FIRSTBITS */
  size = headsize;
  for(i = 0; i < headsize; ++i) {
    unsigned l = maxlens[i];
    if(l > FIRSTBITS) size += (1u << (l - FIRSTBITS));
  }
  tree->table_len = (unsigned char*)lodepng_malloc(size * sizeof(*tree->table_len));
  tree->table_value = (unsigned short*)lodepng_malloc(size * sizeof(*tree->table_value));
  if(!tree->table_len || !tree->table_value) {
    lodepng_free(maxlens);
    /* freeing tree->table values is done at a higher scope */
    return 83; /*alloc fail*/
  }
  /*initialize with an invalid length to indicate unused entries*/
  for(i = 0; i < size; ++i) tree->table_len[i] = 16;

  /*fill in the first table for long symbols: max prefix size and pointer to secondary tables*/
  pointer = headsize;
  for(i = 0; i < headsize; ++i) {
    unsigned l = maxlens[i];
    if(l <= FIRSTBITS) continue;
    tree->table_len[i] = l;
    tree->table_value[i] = pointer;
    pointer += (1u << (l - FIRSTBITS));
  }
  lodepng_free(maxlens);

  /*fill in the first table for short symbols, or secondary table for long symbols*/
  numpresent = 0;
  for(i = 0; i < tree->numcodes; ++i) {
    unsigned l = tree->lengths[i];
    unsigned symbol = tree->codes[i]; /*the huffman bit pattern. i itself is the value.*/
    /*reverse bits, because the huffman bits are given in MSB first order but the bit reader reads LSB first*/
    unsigned reverse = reverseBits(symbol, l);
    if(l == 0) continue;
    numpresent++;

    if(l <= FIRSTBITS) {
      /*short symbol, fully in first table, replicated num times if l < FIRSTBITS*/
      unsigned num = 1u << (FIRSTBITS - l);
      unsigned j;
      for(j = 0; j < num; ++j) {
        /*bit reader will read the l bits of symbol first, the remaining FIRSTBITS - l bits go to the MSB's*/
        unsigned index = reverse | (j << l);
        if(tree->table_len[index] != 16) return 55; /*invalid tree: long symbol shares prefix with short symbol*/
        tree->table_len[index] = l;
        tree->table_value[index] = i;
      }
    } else {
      /*long symbol, shares prefix with other long symbols in first lookup table, needs second lookup*/
      /*the FIRSTBITS MSBs of the symbol are the first table index*/
      unsigned index = reverse & mask;
      unsigned maxlen = tree->table_len[index];
      /*log2 of secondary table length, should be >= l - FIRSTBITS*/
      unsigned tablelen = maxlen - FIRSTBITS;
      unsigned start = tree->table_value[index]; /*starting index in secondary table*/
      unsigned num = 1u << (tablelen - (l - FIRSTBITS)); /*amount of entries of this symbol in secondary table*/
      unsigned j;
      if(maxlen < l) return 55; /*invalid tree: long symbol shares prefix with short symbol*/
      for(j = 0; j < num; ++j) {
        unsigned reverse2 = reverse >> FIRSTBITS; /* l - FIRSTBITS bits */
        unsigned index2 = start + (reverse2 | (j << (l - FIRSTBITS)));
        tree->table_len[index2] = l;
        tree->table_value[index2] = i;
      }
    }
  }

  if(numpresent < 2) {
    /* In case of exactly 1 symbol, in theory the huffman symbol needs 0 bits,
    but deflate uses 1 bit instead. In case of 0 symbols, no symbols can
    appear at all, but such huffman tree could still exist (e.g. if distance
    codes are never used). In both cases, not all symbols of the table will be
    filled in. Fill them in with an invalid symbol value so returning them from
    huffmanDecodeSymbol will cause error. */
    for(i = 0; i < size; ++i) {
      if(tree->table_len[i] == 16) {
        /* As length, use a value smaller than FIRSTBITS for the head table,
        and a value larger than FIRSTBITS for the secondary table, to ensure
        valid behavior for advanceBits when reading this symbol. */
        tree->table_len[i] = (i < headsize) ? 1 : (FIRSTBITS + 1);
        tree->table_value[i] = INVALIDSYMBOL;
      }
    }
  } else {
    /* A good huffman tree has N * 2 - 1 nodes, of which N - 1 are internal nodes.
    If that is not the case (due to too long length codes), the table will not
    have been fully used, and this is an error (not all bit combinations can be
    decoded): an oversubscribed huffman tree, indicated by error 55. */
    for(i = 0; i < size; ++i) {
      if(tree->table_len[i] == 16) return 55;
    }
  }

  return 0;
}

/*
Second step for the ...makeFromLengths and ...makeFromFrequencies functions.
numcodes, lengths and maxbitlen must already be filled in correctly. return
value is error.
*/
static unsigned HuffmanTree_makeFromLengths2(HuffmanTree* tree) {
  unsigned* blcount;
  unsigned* nextcode;
  unsigned error = 0;
  unsigned bits, n;

  tree->codes = (unsigned*)lodepng_malloc(tree->numcodes * sizeof(unsigned));
  blcount = (unsigned*)lodepng_malloc((tree->maxbitlen + 1) * sizeof(unsigned));
  nextcode = (unsigned*)lodepng_malloc((tree->maxbitlen + 1) * sizeof(unsigned));
  if(!tree->codes || !blcount || !nextcode) error = 83; /*alloc fail*/

  if(!error) {
    for(n = 0; n != tree->maxbitlen + 1; n++) blcount[n] = nextcode[n] = 0;
    /*step 1: count number of instances of each code length*/
    for(bits = 0; bits != tree->numcodes; ++bits) ++blcount[tree->lengths[bits]];
    /*step 2: generate the nextcode values*/
    for(bits = 1; bits <= tree->maxbitlen; ++bits) {
      nextcode[bits] = (nextcode[bits - 1] + blcount[bits - 1]) << 1u;
    }
    /*step 3: generate all the codes*/
    for(n = 0; n != tree->numcodes; ++n) {
      if(tree->lengths[n] != 0) {
        tree->codes[n] = nextcode[tree->lengths[n]]++;
        /*remove superfluous bits from the code*/
        tree->codes[n] &= ((1u << tree->lengths[n]) - 1u);
      }
    }
  }

  lodepng_free(blcount);
  lodepng_free(nextcode);

  if(!error) error = HuffmanTree_makeTable(tree);
  return error;
}

/*
given the code lengths (as stored in the PNG file), generate the tree as defined
by Deflate. maxbitlen is the maximum bits that a code in the tree can have.
return value is error.
*/
static unsigned HuffmanTree_makeFromLengths(HuffmanTree* tree, const unsigned* bitlen,
                                            size_t numcodes, unsigned maxbitlen) {
  unsigned i;
  tree->lengths = (unsigned*)lodepng_malloc(numcodes * sizeof(unsigned));
  if(!tree->lengths) return 83; /*alloc fail*/
  for(i = 0; i != numcodes; ++i) tree->lengths[i] = bitlen[i];
  tree->numcodes = (unsigned)numcodes; /*number of symbols*/
  tree->maxbitlen = maxbitlen;
  return HuffmanTree_makeFromLengths2(tree);
}

#ifdef LODEPNG_COMPILE_ENCODER

/*BPM: Boundary Package Merge, see "A Fast and Space-Economical Algorithm for Length-Limited Coding",
Jyrki Katajainen, Alistair Moffat, Andrew Turpin, 1995.*/

/*chain node for boundary package merge*/
typedef struct BPMNode {
  int weight; /*the sum of all weights in this chain*/
  unsigned index; /*index of this leaf node (called "count" in the paper)*/
  struct BPMNode* tail; /*the next nodes in this chain (null if last)*/
  int in_use;
} BPMNode;

/*lists of chains*/
typedef struct BPMLists {
  /*memory pool*/
  unsigned memsize;
  BPMNode* memory;
  unsigned numfree;
  unsigned nextfree;
  BPMNode** freelist;
  /*two heads of lookahead chains per list*/
  unsigned listsize;
  BPMNode** chains0;
  BPMNode** chains1;
} BPMLists;

/*creates a new chain node with the given parameters, from the memory in the lists */
static BPMNode* bpmnode_create(BPMLists* lists, int weight, unsigned index, BPMNode* tail) {
  unsigned i;
  BPMNode* result;

  /*memory full, so garbage collect*/
  if(lists->nextfree >= lists->numfree) {
    /*mark only those that are in use*/
    for(i = 0; i != lists->memsize; ++i) lists->memory[i].in_use = 0;
    for(i = 0; i != lists->listsize; ++i) {
      BPMNode* node;
      for(node = lists->chains0[i]; node != 0; node = node->tail) node->in_use = 1;
      for(node = lists->chains1[i]; node != 0; node = node->tail) node->in_use = 1;
    }
    /*collect those that are free*/
    lists->numfree = 0;
    for(i = 0; i != lists->memsize; ++i) {
      if(!lists->memory[i].in_use) lists->freelist[lists->numfree++] = &lists->memory[i];
    }
    lists->nextfree = 0;
  }

  result = lists->freelist[lists->nextfree++];
  result->weight = weight;
  result->index = index;
  result->tail = tail;
  return result;
}

/*sort the leaves with stable mergesort*/
static void bpmnode_sort(BPMNode* leaves, size_t num) {
  BPMNode* mem = (BPMNode*)lodepng_malloc(sizeof(*leaves) * num);
  size_t width, counter = 0;
  for(width = 1; width < num; width *= 2) {
    BPMNode* a = (counter & 1) ? mem : leaves;
    BPMNode* b = (counter & 1) ? leaves : mem;
    size_t p;
    for(p = 0; p < num; p += 2 * width) {
      size_t q = (p + width > num) ? num : (p + width);
      size_t r = (p + 2 * width > num) ? num : (p + 2 * width);
      size_t i = p, j = q, k;
      for(k = p; k < r; k++) {
        if(i < q && (j >= r || a[i].weight <= a[j].weight)) b[k] = a[i++];
        else b[k] = a[j++];
      }
    }
    counter++;
  }
  if(counter & 1) lodepng_memcpy(leaves, mem, sizeof(*leaves) * num);
  lodepng_free(mem);
}

/*Boundary Package Merge step, numpresent is the amount of leaves, and c is the current chain.*/
static void boundaryPM(BPMLists* lists, BPMNode* leaves, size_t numpresent, int c, int num) {
  unsigned lastindex = lists->chains1[c]->index;

  if(c == 0) {
    if(lastindex >= numpresent) return;
    lists->chains0[c] = lists->chains1[c];
    lists->chains1[c] = bpmnode_create(lists, leaves[lastindex].weight, lastindex + 1, 0);
  } else {
    /*sum of the weights of the head nodes of the previous lookahead chains.*/
    int sum = lists->chains0[c - 1]->weight + lists->chains1[c - 1]->weight;
    lists->chains0[c] = lists->chains1[c];
    if(lastindex < numpresent && sum > leaves[lastindex].weight) {
      lists->chains1[c] = bpmnode_create(lists, leaves[lastindex].weight, lastindex + 1, lists->chains1[c]->tail);
      return;
    }
    lists->chains1[c] = bpmnode_create(lists, sum, lastindex, lists->chains1[c - 1]);
    /*in the end we are only interested in the chain of the last list, so no
    need to recurse if we're at the last one (this gives measurable speedup)*/
    if(num + 1 < (int)(2 * numpresent - 2)) {
      boundaryPM(lists, leaves, numpresent, c - 1, num);
      boundaryPM(lists, leaves, numpresent, c - 1, num);
    }
  }
}

unsigned lodepng_huffman_code_lengths(unsigned* lengths, const unsigned* frequencies,
                                      size_t numcodes, unsigned maxbitlen) {
  unsigned error = 0;
  unsigned i;
  size_t numpresent = 0; /*number of symbols with non-zero frequency*/
  BPMNode* leaves; /*the symbols, only those with > 0 frequency*/

  if(numcodes == 0) return 80; /*error: a tree of 0 symbols is not supposed to be made*/
  if((1u << maxbitlen) < (unsigned)numcodes) return 80; /*error: represent all symbols*/

  leaves = (BPMNode*)lodepng_malloc(numcodes * sizeof(*leaves));
  if(!leaves) return 83; /*alloc fail*/

  for(i = 0; i != numcodes; ++i) {
    if(frequencies[i] > 0) {
      leaves[numpresent].weight = (int)frequencies[i];
      leaves[numpresent].index = i;
      ++numpresent;
    }
  }

  lodepng_memset(lengths, 0, numcodes * sizeof(*lengths));

  /*ensure at least two present symbols. There should be at least one symbol
  according to RFC 1951 section 3.2.7. Some decoders incorrectly require two. To
  make these work as well ensure there are at least two symbols. The
  Package-Merge code below also doesn't work correctly if there's only one
  symbol, it'd give it the theoretical 0 bits but in practice zlib wants 1 bit*/
  if(numpresent == 0) {
    lengths[0] = lengths[1] = 1; /*note that for RFC 1951 section 3.2.7, only lengths[0] = 1 is needed*/
  } else if(numpresent == 1) {
    lengths[leaves[0].index] = 1;
    lengths[leaves[0].index == 0 ? 1 : 0] = 1;
  } else {
    BPMLists lists;
    BPMNode* node;

    bpmnode_sort(leaves, numpresent);

    lists.listsize = maxbitlen;
    lists.memsize = 2 * maxbitlen * (maxbitlen + 1);
    lists.nextfree = 0;
    lists.numfree = lists.memsize;
    lists.memory = (BPMNode*)lodepng_malloc(lists.memsize * sizeof(*lists.memory));
    lists.freelist = (BPMNode**)lodepng_malloc(lists.memsize * sizeof(BPMNode*));
    lists.chains0 = (BPMNode**)lodepng_malloc(lists.listsize * sizeof(BPMNode*));
    lists.chains1 = (BPMNode**)lodepng_malloc(lists.listsize * sizeof(BPMNode*));
    if(!lists.memory || !lists.freelist || !lists.chains0 || !lists.chains1) error = 83; /*alloc fail*/

    if(!error) {
      for(i = 0; i != lists.memsize; ++i) lists.freelist[i] = &lists.memory[i];

      bpmnode_create(&lists, leaves[0].weight, 1, 0);
      bpmnode_create(&lists, leaves[1].weight, 2, 0);

      for(i = 0; i != lists.listsize; ++i) {
        lists.chains0[i] = &lists.memory[0];
        lists.chains1[i] = &lists.memory[1];
      }

      /*each boundaryPM call adds one chain to the last list, and we need 2 * numpresent - 2 chains.*/
      for(i = 2; i != 2 * numpresent - 2; ++i) boundaryPM(&lists, leaves, numpresent, (int)maxbitlen - 1, (int)i);

      for(node = lists.chains1[maxbitlen - 1]; node; node = node->tail) {
        for(i = 0; i != node->index; ++i) ++lengths[leaves[i].index];
      }
    }

    lodepng_free(lists.memory);
    lodepng_free(lists.freelist);
    lodepng_free(lists.chains0);
    lodepng_free(lists.chains1);
  }

  lodepng_free(leaves);
  return error;
}

/*Create the Huffman tree given the symbol frequencies*/
static unsigned HuffmanTree_makeFromFrequencies(HuffmanTree* tree, const unsigned* frequencies,
                                                size_t mincodes, size_t numcodes, unsigned maxbitlen) {
  unsigned error = 0;
  while(!frequencies[numcodes - 1] && numcodes > mincodes) --numcodes; /*trim zeroes*/
  tree->lengths = (unsigned*)lodepng_malloc(numcodes * sizeof(unsigned));
  if(!tree->lengths) return 83; /*alloc fail*/
  tree->maxbitlen = maxbitlen;
  tree->numcodes = (unsigned)numcodes; /*number of symbols*/

  error = lodepng_huffman_code_lengths(tree->lengths, frequencies, numcodes, maxbitlen);
  if(!error) error = HuffmanTree_makeFromLengths2(tree);
  return error;
}
#endif /*LODEPNG_COMPILE_ENCODER*/

/*get the literal and length code tree of a deflated block with fixed tree, as per the deflate specification*/
static unsigned generateFixedLitLenTree(HuffmanTree* tree) {
  unsigned i, error = 0;
  unsigned* bitlen = (unsigned*)lodepng_malloc(NUM_DEFLATE_CODE_SYMBOLS * sizeof(unsigned));
  if(!bitlen) return 83; /*alloc fail*/

  /*288 possible codes: 0-255=literals, 256=endcode, 257-285=lengthcodes, 286-287=unused*/
  for(i =   0; i <= 143; ++i) bitlen[i] = 8;
  for(i = 144; i <= 255; ++i) bitlen[i] = 9;
  for(i = 256; i <= 279; ++i) bitlen[i] = 7;
  for(i = 280; i <= 287; ++i) bitlen[i] = 8;

  error = HuffmanTree_makeFromLengths(tree, bitlen, NUM_DEFLATE_CODE_SYMBOLS, 15);

  lodepng_free(bitlen);
  return error;
}

/*get the distance code tree of a deflated block with fixed tree, as specified in the deflate specification*/
static unsigned generateFixedDistanceTree(HuffmanTree* tree) {
  unsigned i, error = 0;
  unsigned* bitlen = (unsigned*)lodepng_malloc(NUM_DISTANCE_SYMBOLS * sizeof(unsigned));
  if(!bitlen) return 83; /*alloc fail*/

  /*there are 32 distance codes, but 30-31 are unused*/
  for(i = 0; i != NUM_DISTANCE_SYMBOLS; ++i) bitlen[i] = 5;
  error = HuffmanTree_makeFromLengths(tree, bitlen, NUM_DISTANCE_SYMBOLS, 15);

  lodepng_free(bitlen);
  return error;
}

/* ////////////////////////////////////////////////////////////////////////// */
/* / Deflator (Compressor)                                                  / */
/* ////////////////////////////////////////////////////////////////////////// */

static const size_t MAX_SUPPORTED_DEFLATE_LENGTH = 258;

/*search the index in the array, that has the largest value smaller than or equal to the given value,
given array must be sorted (if no value is smaller, it returns the size of the given array)*/
static size_t searchCodeIndex(const unsigned* array, size_t array_size, size_t value) {
  /*binary search (only small gain over linear). TODO: use CPU log2 instruction for getting symbols instead*/
  size_t left = 1;
  size_t right = array_size - 1;

  while(left <= right) {
    size_t mid = (left + right) >> 1;
    if(array[mid] >= value) right = mid - 1;
    else left = mid + 1;
  }
  if(left >= array_size || array[left] > value) left--;
  return left;
}

static void addLengthDistance(uivector* values, size_t length, size_t distance) {
  /*values in encoded vector are those used by deflate:
  0-255: literal bytes
  256: end
  257-285: length/distance pair (length code, followed by extra length bits, distance code, extra distance bits)
  286-287: invalid*/

  unsigned length_code = (unsigned)searchCodeIndex(LENGTHBASE, 29, length);
  unsigned extra_length = (unsigned)(length - LENGTHBASE[length_code]);
  unsigned dist_code = (unsigned)searchCodeIndex(DISTANCEBASE, 30, distance);
  unsigned extra_distance = (unsigned)(distance - DISTANCEBASE[dist_code]);

  size_t pos = values->size;
  /*TODO: return error when this fails (out of memory)*/
  unsigned ok = uivector_resize(values, values->size + 4);
  if(ok) {
    values->data[pos + 0] = length_code + FIRST_LENGTH_CODE_INDEX;
    values->data[pos + 1] = extra_length;
    values->data[pos + 2] = dist_code;
    values->data[pos + 3] = extra_distance;
  }
}

/*
LZ77-encode the data. Return value is error code. The input are raw bytes, the output
is in the form of unsigned integers with codes representing for example literal bytes, or
length/distance pairs.
It uses a hash table technique to let it encode faster. When doing LZ77 encoding, a
sliding window (of windowsize) is used, and all past bytes in that window can be used as
the "dictionary". A brute force search through all possible distances would be slow, and
this hash technique is one out of several ways to speed this up.
*/
static unsigned encodeLZ77(uivector* out, const unsigned char* in,
                           size_t inpos, size_t insize, unsigned windowsize,
                           unsigned minmatch) {
  unsigned error = 0;

  unsigned i;
  int j;

  unsigned offset; /*the offset represents the distance in LZ77 terminology*/
  unsigned length;
  unsigned char current_value;
  unsigned char* matchs, *prev_matchs;
  unsigned has_matches = 0;
  int last_back_pos;

  matchs = (unsigned char*)lodepng_malloc(windowsize*sizeof(unsigned char));
  prev_matchs = (unsigned char*)lodepng_malloc(windowsize*sizeof(unsigned char));

  for (j = 0; j < windowsize; ++j) {
    matchs[j] = 0;
    prev_matchs[j] = 0;
  }

  length = 0;
  offset = 0;

  if(windowsize == 0 || windowsize > 32768) return 60; /*error: windowsize smaller/larger than allowed*/
  if((windowsize & (windowsize - 1)) != 0) return 90; /*error: must be power of two*/

  for(i = inpos; i < insize; ++i) {
    current_value = in[i];  /*the character that may be repeated*/
    
    if (i <= windowsize)
      last_back_pos = 0;
    else
      last_back_pos = (int) (i - windowsize);

    /*populate the matchs vector*/
    for(j=(int) (i-1); j >= last_back_pos; j--) { /*For each position in the window*/
      matchs[i - j - 1] = (prev_matchs[i - j - 1] == 1) && (in[j] == current_value);
      if (matchs[i - j - 1])
        has_matches = 1;
    }
    
    length += 1;
    if (has_matches && length < MAX_SUPPORTED_DEFLATE_LENGTH) {
      for (j = 0; j < windowsize; ++j)
        prev_matchs[j] = matchs[j];
    } else { /*end of match*/
      for(j=i-1; j >= last_back_pos; j--) { 
        /*find the smallest offset*/
        if (prev_matchs[i - j - 1] == 1 && offset == 0)
          offset = i - j;
        /*Reset the matches*/
        prev_matchs[i - j - 1] = (in[j] == current_value);
      }


      /*encode it as length/distance pair or literal value*/
      if(i>0) {
        if(length >= 3 && offset > windowsize) ERROR_BREAK(86 /*too big (or overflown negative) offset*/);
        
        if(length < 3) { /*only lengths of 3 or higher are supported as length/distance pair*/
          if (length == 2) {//First byte of the pair
            //printf("Literal: %u\n", in[i-2]);
            if(!uivector_push_back(out, in[i-2])) ERROR_BREAK(83 /*alloc fail*/);
          }
          //printf("Literal: %u\n", in[i-1]);
          if(!uivector_push_back(out, in[i-1])) ERROR_BREAK(83 /*alloc fail*/);
        } else {
          //printf("Length: %u, Offset: %u\n", length, offset);
          addLengthDistance(out, length, offset);
        }
      }
      offset = 0;
      length = 0;
    }
    has_matches = 0;
  } /*end of the loop through each character of input*/

  /*encode the last length/distance pair or literal value*/
  i = insize-1;
  if (i <= windowsize)
    last_back_pos = 0;
  else
    last_back_pos = (int) (i - windowsize);

  for(j=(int) (i-1); j >= last_back_pos; j--) {
    if (matchs[i - j - 1])
      has_matches = 1;
  }

  if (has_matches) {
    length += 1;
    for(j=i-1; j >= last_back_pos; j--) { 
      /*find the smallest offset*/
      if (matchs[i - j - 1] == 1 && offset == 0)
        offset = i - j;
    }
  }

  if(length < 3) {
    if (length == 2) {
      //printf("Last Literal2: %u\n", in[i-1]);
      if(!uivector_push_back(out, in[i-1])) return 83; /*alloc fail*/
    }
    //printf("Last Literal1: %u\n", in[i]);
    if(!uivector_push_back(out, in[i])) return 83; /*alloc fail*/
  } else {
    //printf("Last Length: %u, Offset: %u\n", length, offset);
    addLengthDistance(out, length, offset);
  }

  free(matchs);
  free(prev_matchs);

  return error;
}

/* /////////////////////////////////////////////////////////////////////////// */

/*
write the lz77-encoded data, which has lit, len and dist codes, to compressed stream using huffman trees.
tree_ll: the tree for lit and len codes.
tree_d: the tree for distance codes.
*/
static void writeLZ77data(LodePNGBitWriter* writer, const uivector* lz77_encoded,
                          const HuffmanTree* tree_ll, const HuffmanTree* tree_d) {
  size_t i = 0;
  for(i = 0; i != lz77_encoded->size; ++i) {
    unsigned val = lz77_encoded->data[i];
    writeBitsReversed(writer, tree_ll->codes[val], tree_ll->lengths[val]);
    //printf("Code: %u, Length: %u\n", tree_ll->codes[val], tree_ll->lengths[val]);
    if(val > 256) /*for a length code, 3 more things have to be added*/ {
      unsigned length_index = val - FIRST_LENGTH_CODE_INDEX;
      unsigned n_length_extra_bits = LENGTHEXTRA[length_index];
      unsigned length_extra_bits = lz77_encoded->data[++i];

      unsigned distance_code = lz77_encoded->data[++i];

      unsigned distance_index = distance_code;
      unsigned n_distance_extra_bits = DISTANCEEXTRA[distance_index];
      unsigned distance_extra_bits = lz77_encoded->data[++i];

      writeBits(writer, length_extra_bits, n_length_extra_bits);
      //printf("(Revert) Code: %u, Length: %u\n", length_extra_bits, n_length_extra_bits);
      writeBitsReversed(writer, tree_d->codes[distance_code], tree_d->lengths[distance_code]);
      //printf("Code: %u, Length: %u\n", tree_d->codes[distance_code], tree_d->lengths[distance_code]);
      writeBits(writer, distance_extra_bits, n_distance_extra_bits);
      //printf("(Revert) Code: %u, Length: %u\n", distance_extra_bits, n_distance_extra_bits);
    }
  }
}

static unsigned deflateFixed(LodePNGBitWriter* writer,
                             const unsigned char* data,
                             size_t datapos, size_t dataend,
                             const LodePNGCompressSettings* settings, unsigned final) {
  HuffmanTree tree_ll; /*tree for literal values and length codes*/
  HuffmanTree tree_d; /*tree for distance codes*/

  unsigned BFINAL = final;
  unsigned error = 0;
  size_t i;

  HuffmanTree_init(&tree_ll);
  HuffmanTree_init(&tree_d);

  error = generateFixedLitLenTree(&tree_ll);
  if(!error) error = generateFixedDistanceTree(&tree_d);

  if(!error) {
    writeBits(writer, BFINAL, 1);
    writeBits(writer, 1, 1); /*first bit of BTYPE*/
    writeBits(writer, 0, 1); /*second bit of BTYPE*/

    uivector lz77_encoded;
    uivector_init(&lz77_encoded);
    error = encodeLZ77(&lz77_encoded, data, datapos, dataend, settings->windowsize,
                        settings->minmatch);
    if(!error) writeLZ77data(writer, &lz77_encoded, &tree_ll, &tree_d);
    uivector_cleanup(&lz77_encoded);

    /*add END code*/
    if(!error) writeBitsReversed(writer,tree_ll.codes[256], tree_ll.lengths[256]);
  }

  /*cleanup*/
  HuffmanTree_cleanup(&tree_ll);
  HuffmanTree_cleanup(&tree_d);

  return error;
}

static unsigned lodepng_deflatev(ucvector* out, const unsigned char* in, size_t insize,
                                 const LodePNGCompressSettings* settings) {
  unsigned error = 0;
  size_t blocksize, numdeflateblocks;
  LodePNGBitWriter writer;

  LodePNGBitWriter_init(&writer, out);

  if(settings->btype != 1) return 61;
  else blocksize = insize; 

  if(!error) {
      error = deflateFixed(&writer, in, 0, insize, settings, 1);
  }

  return error;
}

unsigned lodepng_deflate(unsigned char** out, size_t* outsize,
                         const unsigned char* in, size_t insize,
                         const LodePNGCompressSettings* settings) {
  ucvector v = ucvector_init(*out, *outsize);
  unsigned error = lodepng_deflatev(&v, in, insize, settings);
  *out = v.data;
  *outsize = v.size;
  return error;
}

static unsigned deflate(unsigned char** out, size_t* outsize,
                        const unsigned char* in, size_t insize,
                        const LodePNGCompressSettings* settings) {
  if(settings->custom_deflate) {
    return settings->custom_deflate(out, outsize, in, insize, settings);
  } else {
    return lodepng_deflate(out, outsize, in, insize, settings);
  }
}

/* ////////////////////////////////////////////////////////////////////////// */
/* / Adler32                                                                / */
/* ////////////////////////////////////////////////////////////////////////// */

static unsigned update_adler32(unsigned adler, const unsigned char* data, unsigned len) {
  unsigned s1 = adler & 0xffffu;
  unsigned s2 = (adler >> 16u) & 0xffffu;

  while(len != 0u) {
    unsigned i;
    /*at least 5552 sums can be done before the sums overflow, saving a lot of module divisions*/
    unsigned amount = len > 5552u ? 5552u : len;
    len -= amount;
    for(i = 0; i != amount; ++i) {
      s1 += (*data++);
      s2 += s1;
    }
    s1 %= 65521u;
    s2 %= 65521u;
  }

  return (s2 << 16u) | s1;
}

/*Return the adler32 of the bytes data[0..len-1]*/
static unsigned adler32(const unsigned char* data, unsigned len) {
  return update_adler32(1u, data, len);
}

/* ////////////////////////////////////////////////////////////////////////// */
/* / Zlib                                                                   / */
/* ////////////////////////////////////////////////////////////////////////// */

#ifdef LODEPNG_COMPILE_ENCODER

unsigned lodepng_zlib_compress(unsigned char** out, size_t* outsize, const unsigned char* in,
                               size_t insize, const LodePNGCompressSettings* settings) {
  size_t i;
  unsigned error;
  unsigned char* deflatedata = 0;
  size_t deflatesize = 0;

  error = deflate(&deflatedata, &deflatesize, in, insize, settings);

  *out = NULL;
  *outsize = 0;
  if(!error) {
    *outsize = deflatesize + 6;
    *out = (unsigned char*)lodepng_malloc(*outsize);
    if(!*out) error = 83; /*alloc fail*/
  }

  if(!error) {
    unsigned ADLER32 = adler32(in, (unsigned)insize);
    /*zlib data: 1 byte CMF (CM+CINFO), 1 byte FLG, deflate data, 4 byte ADLER32 checksum of the Decompressed data*/
    unsigned CMF = 120; /*0b01111000: CM 8, CINFO 7. With CINFO 7, any window size up to 32768 can be used.*/
    unsigned FLEVEL = 0;
    unsigned FDICT = 0;
    unsigned CMFFLG = 256 * CMF + FDICT * 32 + FLEVEL * 64;
    unsigned FCHECK = 31 - CMFFLG % 31;
    CMFFLG += FCHECK;

    (*out)[0] = (unsigned char)(CMFFLG >> 8);
    (*out)[1] = (unsigned char)(CMFFLG & 255);
    for(i = 0; i != deflatesize; ++i) (*out)[i + 2] = deflatedata[i];
    lodepng_set32bitInt(&(*out)[*outsize - 4], ADLER32);
  }

  //print out vector
  //for (unsigned int i = 2; i < *outsize-6; i++) {
    //printf("out[%u]: %02X\n", i, (*out)[i]);
  //}

  lodepng_free(deflatedata);
  return error;
}

/* compress using the default or custom zlib function */
static unsigned zlib_compress(unsigned char** out, size_t* outsize, const unsigned char* in,
                              size_t insize, const LodePNGCompressSettings* settings) {
  if(settings->custom_zlib) {
    return settings->custom_zlib(out, outsize, in, insize, settings);
  } else {
    return lodepng_zlib_compress(out, outsize, in, insize, settings);
  }
}

#endif /*LODEPNG_COMPILE_ENCODER*/

#else /*no LODEPNG_COMPILE_ZLIB*/
#ifdef LODEPNG_COMPILE_ENCODER
static unsigned zlib_compress(unsigned char** out, size_t* outsize, const unsigned char* in,
                              size_t insize, const LodePNGCompressSettings* settings) {
  if(!settings->custom_zlib) return 87; /*no custom zlib function provided */
  return settings->custom_zlib(out, outsize, in, insize, settings);
}
#endif /*LODEPNG_COMPILE_ENCODER*/

#endif /*LODEPNG_COMPILE_ZLIB*/

/* ////////////////////////////////////////////////////////////////////////// */

#ifdef LODEPNG_COMPILE_ENCODER

/*this is a good tradeoff between speed and compression ratio*/
#define DEFAULT_WINDOWSIZE 512

void lodepng_compress_settings_init(LodePNGCompressSettings* settings) {
  /*compress with static huffman tree*/
  settings->btype = 1;
  settings->use_lz77 = 1;
  settings->windowsize = DEFAULT_WINDOWSIZE;
  settings->minmatch = 3;
  settings->nicematch = 2048;
  settings->lazymatching = 0;

  settings->custom_zlib = 0;
  settings->custom_deflate = 0;
  settings->custom_context = 0;
}

const LodePNGCompressSettings lodepng_default_compress_settings = {2, 1, DEFAULT_WINDOWSIZE, 3, 128, 1, 0, 0, 0};


#endif /*LODEPNG_COMPILE_ENCODER*/

/* ////////////////////////////////////////////////////////////////////////// */
/* ////////////////////////////////////////////////////////////////////////// */
/* // End of Zlib related code. Begin of PNG related code.                 // */
/* ////////////////////////////////////////////////////////////////////////// */
/* ////////////////////////////////////////////////////////////////////////// */

#ifdef LODEPNG_COMPILE_PNG

/* ////////////////////////////////////////////////////////////////////////// */
/* / CRC32                                                                  / */
/* ////////////////////////////////////////////////////////////////////////// */


#ifndef LODEPNG_NO_COMPILE_CRC
/* CRC polynomial: 0xedb88320 */
static unsigned lodepng_crc32_table[256] = {
           0u, 1996959894u, 3993919788u, 2567524794u,  124634137u, 1886057615u, 3915621685u, 2657392035u,
   249268274u, 2044508324u, 3772115230u, 2547177864u,  162941995u, 2125561021u, 3887607047u, 2428444049u,
   498536548u, 1789927666u, 4089016648u, 2227061214u,  450548861u, 1843258603u, 4107580753u, 2211677639u,
   325883990u, 1684777152u, 4251122042u, 2321926636u,  335633487u, 1661365465u, 4195302755u, 2366115317u,
   997073096u, 1281953886u, 3579855332u, 2724688242u, 1006888145u, 1258607687u, 3524101629u, 2768942443u,
   901097722u, 1119000684u, 3686517206u, 2898065728u,  853044451u, 1172266101u, 3705015759u, 2882616665u,
   651767980u, 1373503546u, 3369554304u, 3218104598u,  565507253u, 1454621731u, 3485111705u, 3099436303u,
   671266974u, 1594198024u, 3322730930u, 2970347812u,  795835527u, 1483230225u, 3244367275u, 3060149565u,
  1994146192u,   31158534u, 2563907772u, 4023717930u, 1907459465u,  112637215u, 2680153253u, 3904427059u,
  2013776290u,  251722036u, 2517215374u, 3775830040u, 2137656763u,  141376813u, 2439277719u, 3865271297u,
  1802195444u,  476864866u, 2238001368u, 4066508878u, 1812370925u,  453092731u, 2181625025u, 4111451223u,
  1706088902u,  314042704u, 2344532202u, 4240017532u, 1658658271u,  366619977u, 2362670323u, 4224994405u,
  1303535960u,  984961486u, 2747007092u, 3569037538u, 1256170817u, 1037604311u, 2765210733u, 3554079995u,
  1131014506u,  879679996u, 2909243462u, 3663771856u, 1141124467u,  855842277u, 2852801631u, 3708648649u,
  1342533948u,  654459306u, 3188396048u, 3373015174u, 1466479909u,  544179635u, 3110523913u, 3462522015u,
  1591671054u,  702138776u, 2966460450u, 3352799412u, 1504918807u,  783551873u, 3082640443u, 3233442989u,
  3988292384u, 2596254646u,   62317068u, 1957810842u, 3939845945u, 2647816111u,   81470997u, 1943803523u,
  3814918930u, 2489596804u,  225274430u, 2053790376u, 3826175755u, 2466906013u,  167816743u, 2097651377u,
  4027552580u, 2265490386u,  503444072u, 1762050814u, 4150417245u, 2154129355u,  426522225u, 1852507879u,
  4275313526u, 2312317920u,  282753626u, 1742555852u, 4189708143u, 2394877945u,  397917763u, 1622183637u,
  3604390888u, 2714866558u,  953729732u, 1340076626u, 3518719985u, 2797360999u, 1068828381u, 1219638859u,
  3624741850u, 2936675148u,  906185462u, 1090812512u, 3747672003u, 2825379669u,  829329135u, 1181335161u,
  3412177804u, 3160834842u,  628085408u, 1382605366u, 3423369109u, 3138078467u,  570562233u, 1426400815u,
  3317316542u, 2998733608u,  733239954u, 1555261956u, 3268935591u, 3050360625u,  752459403u, 1541320221u,
  2607071920u, 3965973030u, 1969922972u,   40735498u, 2617837225u, 3943577151u, 1913087877u,   83908371u,
  2512341634u, 3803740692u, 2075208622u,  213261112u, 2463272603u, 3855990285u, 2094854071u,  198958881u,
  2262029012u, 4057260610u, 1759359992u,  534414190u, 2176718541u, 4139329115u, 1873836001u,  414664567u,
  2282248934u, 4279200368u, 1711684554u,  285281116u, 2405801727u, 4167216745u, 1634467795u,  376229701u,
  2685067896u, 3608007406u, 1308918612u,  956543938u, 2808555105u, 3495958263u, 1231636301u, 1047427035u,
  2932959818u, 3654703836u, 1088359270u,  936918000u, 2847714899u, 3736837829u, 1202900863u,  817233897u,
  3183342108u, 3401237130u, 1404277552u,  615818150u, 3134207493u, 3453421203u, 1423857449u,  601450431u,
  3009837614u, 3294710456u, 1567103746u,  711928724u, 3020668471u, 3272380065u, 1510334235u,  755167117u
};

/*Return the CRC of the bytes buf[0..len-1].*/
unsigned lodepng_crc32(const unsigned char* data, size_t length) {
  unsigned r = 0xffffffffu;
  size_t i;
  for(i = 0; i < length; ++i) {
    r = lodepng_crc32_table[(r ^ data[i]) & 0xffu] ^ (r >> 8u);
  }
  return r ^ 0xffffffffu;
}
#else /* !LODEPNG_NO_COMPILE_CRC */
unsigned lodepng_crc32(const unsigned char* data, size_t length);
#endif /* !LODEPNG_NO_COMPILE_CRC */

/* ////////////////////////////////////////////////////////////////////////// */
/* / Reading and writing PNG color channel bits                             / */
/* ////////////////////////////////////////////////////////////////////////// */

/* The color channel bits of less-than-8-bit pixels are read with the MSB of bytes first,
so LodePNGBitWriter and LodePNGBitReader can't be used for those. */

static unsigned char readBitFromReversedStream(size_t* bitpointer, const unsigned char* bitstream) {
  unsigned char result = (unsigned char)((bitstream[(*bitpointer) >> 3] >> (7 - ((*bitpointer) & 0x7))) & 1);
  ++(*bitpointer);
  return result;
}

/* TODO: make this faster */
static unsigned readBitsFromReversedStream(size_t* bitpointer, const unsigned char* bitstream, size_t nbits) {
  unsigned result = 0;
  size_t i;
  for(i = 0 ; i < nbits; ++i) {
    result <<= 1u;
    result |= (unsigned)readBitFromReversedStream(bitpointer, bitstream);
  }
  return result;
}

static void setBitOfReversedStream(size_t* bitpointer, unsigned char* bitstream, unsigned char bit) {
  /*the current bit in bitstream may be 0 or 1 for this to work*/
  if(bit == 0) bitstream[(*bitpointer) >> 3u] &=  (unsigned char)(~(1u << (7u - ((*bitpointer) & 7u))));
  else         bitstream[(*bitpointer) >> 3u] |=  (1u << (7u - ((*bitpointer) & 7u)));
  ++(*bitpointer);
}

/* ////////////////////////////////////////////////////////////////////////// */
/* / PNG chunks                                                             / */
/* ////////////////////////////////////////////////////////////////////////// */

unsigned lodepng_chunk_length(const unsigned char* chunk) {
  return lodepng_read32bitInt(&chunk[0]);
}

void lodepng_chunk_type(char type[5], const unsigned char* chunk) {
  unsigned i;
  for(i = 0; i != 4; ++i) type[i] = (char)chunk[4 + i];
  type[4] = 0; /*null termination char*/
}

unsigned char lodepng_chunk_type_equals(const unsigned char* chunk, const char* type) {
  if(lodepng_strlen(type) != 4) return 0;
  return (chunk[4] == type[0] && chunk[5] == type[1] && chunk[6] == type[2] && chunk[7] == type[3]);
}

unsigned char lodepng_chunk_ancillary(const unsigned char* chunk) {
  return((chunk[4] & 32) != 0);
}

unsigned char lodepng_chunk_private(const unsigned char* chunk) {
  return((chunk[6] & 32) != 0);
}

unsigned char lodepng_chunk_safetocopy(const unsigned char* chunk) {
  return((chunk[7] & 32) != 0);
}

unsigned char* lodepng_chunk_data(unsigned char* chunk) {
  return &chunk[8];
}

const unsigned char* lodepng_chunk_data_const(const unsigned char* chunk) {
  return &chunk[8];
}

unsigned lodepng_chunk_check_crc(const unsigned char* chunk) {
  unsigned length = lodepng_chunk_length(chunk);
  unsigned CRC = lodepng_read32bitInt(&chunk[length + 8]);
  /*the CRC is taken of the data and the 4 chunk type letters, not the length*/
  unsigned checksum = lodepng_crc32(&chunk[4], length + 4);
  if(CRC != checksum) return 1;
  else return 0;
}

void lodepng_chunk_generate_crc(unsigned char* chunk) {
  unsigned length = lodepng_chunk_length(chunk);
  unsigned CRC = lodepng_crc32(&chunk[4], length + 4);
  lodepng_set32bitInt(chunk + 8 + length, CRC);
}

unsigned char* lodepng_chunk_next(unsigned char* chunk, unsigned char* end) {
  if(chunk >= end || end - chunk < 12) return end; /*too small to contain a chunk*/
  if(chunk[0] == 0x89 && chunk[1] == 0x50 && chunk[2] == 0x4e && chunk[3] == 0x47
    && chunk[4] == 0x0d && chunk[5] == 0x0a && chunk[6] == 0x1a && chunk[7] == 0x0a) {
    /* Is PNG magic header at start of PNG file. Jump to first actual chunk. */
    return chunk + 8;
  } else {
    size_t total_chunk_length;
    unsigned char* result;
    if(lodepng_addofl(lodepng_chunk_length(chunk), 12, &total_chunk_length)) return end;
    result = chunk + total_chunk_length;
    if(result < chunk) return end; /*pointer overflow*/
    return result;
  }
}

const unsigned char* lodepng_chunk_next_const(const unsigned char* chunk, const unsigned char* end) {
  if(chunk >= end || end - chunk < 12) return end; /*too small to contain a chunk*/
  if(chunk[0] == 0x89 && chunk[1] == 0x50 && chunk[2] == 0x4e && chunk[3] == 0x47
    && chunk[4] == 0x0d && chunk[5] == 0x0a && chunk[6] == 0x1a && chunk[7] == 0x0a) {
    /* Is PNG magic header at start of PNG file. Jump to first actual chunk. */
    return chunk + 8;
  } else {
    size_t total_chunk_length;
    const unsigned char* result;
    if(lodepng_addofl(lodepng_chunk_length(chunk), 12, &total_chunk_length)) return end;
    result = chunk + total_chunk_length;
    if(result < chunk) return end; /*pointer overflow*/
    return result;
  }
}

unsigned char* lodepng_chunk_find(unsigned char* chunk, unsigned char* end, const char type[5]) {
  for(;;) {
    if(chunk >= end || end - chunk < 12) return 0; /* past file end: chunk + 12 > end */
    if(lodepng_chunk_type_equals(chunk, type)) return chunk;
    chunk = lodepng_chunk_next(chunk, end);
  }
}

const unsigned char* lodepng_chunk_find_const(const unsigned char* chunk, const unsigned char* end, const char type[5]) {
  for(;;) {
    if(chunk >= end || end - chunk < 12) return 0; /* past file end: chunk + 12 > end */
    if(lodepng_chunk_type_equals(chunk, type)) return chunk;
    chunk = lodepng_chunk_next_const(chunk, end);
  }
}

unsigned lodepng_chunk_append(unsigned char** out, size_t* outsize, const unsigned char* chunk) {
  unsigned i;
  size_t total_chunk_length, new_length;
  unsigned char *chunk_start, *new_buffer;

  if(lodepng_addofl(lodepng_chunk_length(chunk), 12, &total_chunk_length)) return 77;
  if(lodepng_addofl(*outsize, total_chunk_length, &new_length)) return 77;

  new_buffer = (unsigned char*)lodepng_realloc(*out, new_length);
  if(!new_buffer) return 83; /*alloc fail*/
  (*out) = new_buffer;
  (*outsize) = new_length;
  chunk_start = &(*out)[new_length - total_chunk_length];

  for(i = 0; i != total_chunk_length; ++i) chunk_start[i] = chunk[i];

  return 0;
}

/*Sets length and name and allocates the space for data and crc but does not
set data or crc yet. Returns the start of the chunk in chunk. The start of
the data is at chunk + 8. To finalize chunk, add the data, then use
lodepng_chunk_generate_crc */
static unsigned lodepng_chunk_init(unsigned char** chunk,
                                   ucvector* out,
                                   unsigned length, const char* type) {
  size_t new_length = out->size;
  if(lodepng_addofl(new_length, length, &new_length)) return 77;
  if(lodepng_addofl(new_length, 12, &new_length)) return 77;
  if(!ucvector_resize(out, new_length)) return 83; /*alloc fail*/
  *chunk = out->data + new_length - length - 12u;

  /*1: length*/
  lodepng_set32bitInt(*chunk, length);

  /*2: chunk name (4 letters)*/
  lodepng_memcpy(*chunk + 4, type, 4);

  return 0;
}

/* like lodepng_chunk_create but with custom allocsize */
static unsigned lodepng_chunk_createv(ucvector* out,
                                      unsigned length, const char* type, const unsigned char* data) {
  unsigned char* chunk;
  CERROR_TRY_RETURN(lodepng_chunk_init(&chunk, out, length, type));

  /*3: the data*/
  lodepng_memcpy(chunk + 8, data, length);

  /*4: CRC (of the chunkname characters and the data)*/
  lodepng_chunk_generate_crc(chunk);

  return 0;
}

unsigned lodepng_chunk_create(unsigned char** out, size_t* outsize,
                              unsigned length, const char* type, const unsigned char* data) {
  ucvector v = ucvector_init(*out, *outsize);
  unsigned error = lodepng_chunk_createv(&v, length, type, data);
  *out = v.data;
  *outsize = v.size;
  return error;
}

/* ////////////////////////////////////////////////////////////////////////// */
/* / Color types, channels, bits                                            / */
/* ////////////////////////////////////////////////////////////////////////// */

/*checks if the colortype is valid and the bitdepth bd is allowed for this colortype.
Return value is a LodePNG error code.*/
static unsigned checkColorValidity(LodePNGColorType colortype, unsigned bd) {
  switch(colortype) {
    case LCT_GREY:       if(!(bd == 1 || bd == 2 || bd == 4 || bd == 8 || bd == 16)) return 37; break;
    case LCT_RGB:        if(!(                                 bd == 8 || bd == 16)) return 37; break;
    case LCT_PALETTE:    if(!(bd == 1 || bd == 2 || bd == 4 || bd == 8            )) return 37; break;
    case LCT_GREY_ALPHA: if(!(                                 bd == 8 || bd == 16)) return 37; break;
    case LCT_RGBA:       if(!(                                 bd == 8 || bd == 16)) return 37; break;
    case LCT_MAX_OCTET_VALUE: return 31; /* invalid color type */
    default: return 31; /* invalid color type */
  }
  return 0; /*allowed color type / bits combination*/
}

static unsigned getNumColorChannels(LodePNGColorType colortype) {
  switch(colortype) {
    case LCT_GREY: return 1;
    case LCT_RGB: return 3;
    case LCT_PALETTE: return 1;
    case LCT_GREY_ALPHA: return 2;
    case LCT_RGBA: return 4;
    case LCT_MAX_OCTET_VALUE: return 0; /* invalid color type */
    default: return 0; /*invalid color type*/
  }
}

static unsigned lodepng_get_bpp_lct(LodePNGColorType colortype, unsigned bitdepth) {
  /*bits per pixel is amount of channels * bits per channel*/
  return getNumColorChannels(colortype) * bitdepth;
}

/* ////////////////////////////////////////////////////////////////////////// */

void lodepng_color_mode_init(LodePNGColorMode* info) {
  info->key_defined = 0;
  info->key_r = info->key_g = info->key_b = 0;
  info->colortype = LCT_RGBA;
  info->bitdepth = 8;
  info->palette = 0;
  info->palettesize = 0;
}

/*allocates palette memory if needed, and initializes all colors to black*/
static void lodepng_color_mode_alloc_palette(LodePNGColorMode* info) {
  size_t i;
  /*if the palette is already allocated, it will have size 1024 so no reallocation needed in that case*/
  /*the palette must have room for up to 256 colors with 4 bytes each.*/
  if(!info->palette) info->palette = (unsigned char*)lodepng_malloc(1024);
  if(!info->palette) return; /*alloc fail*/
  for(i = 0; i != 256; ++i) {
    /*Initialize all unused colors with black, the value used for invalid palette indices.
    This is an error according to the PNG spec, but common PNG decoders make it black instead.
    That makes color conversion slightly faster due to no error handling needed.*/
    info->palette[i * 4 + 0] = 0;
    info->palette[i * 4 + 1] = 0;
    info->palette[i * 4 + 2] = 0;
    info->palette[i * 4 + 3] = 255;
  }
}

void lodepng_color_mode_cleanup(LodePNGColorMode* info) {
  lodepng_palette_clear(info);
}

unsigned lodepng_color_mode_copy(LodePNGColorMode* dest, const LodePNGColorMode* source) {
  lodepng_color_mode_cleanup(dest);
  lodepng_memcpy(dest, source, sizeof(LodePNGColorMode));
  if(source->palette) {
    dest->palette = (unsigned char*)lodepng_malloc(1024);
    if(!dest->palette && source->palettesize) return 83; /*alloc fail*/
    lodepng_memcpy(dest->palette, source->palette, source->palettesize * 4);
  }
  return 0;
}

LodePNGColorMode lodepng_color_mode_make(LodePNGColorType colortype, unsigned bitdepth) {
  LodePNGColorMode result;
  lodepng_color_mode_init(&result);
  result.colortype = colortype;
  result.bitdepth = bitdepth;
  return result;
}

static int lodepng_color_mode_equal(const LodePNGColorMode* a, const LodePNGColorMode* b) {
  size_t i;
  if(a->colortype != b->colortype) return 0;
  if(a->bitdepth != b->bitdepth) return 0;
  if(a->key_defined != b->key_defined) return 0;
  if(a->key_defined) {
    if(a->key_r != b->key_r) return 0;
    if(a->key_g != b->key_g) return 0;
    if(a->key_b != b->key_b) return 0;
  }
  if(a->palettesize != b->palettesize) return 0;
  for(i = 0; i != a->palettesize * 4; ++i) {
    if(a->palette[i] != b->palette[i]) return 0;
  }
  return 1;
}

void lodepng_palette_clear(LodePNGColorMode* info) {
  if(info->palette) lodepng_free(info->palette);
  info->palette = 0;
  info->palettesize = 0;
}

unsigned lodepng_palette_add(LodePNGColorMode* info,
                             unsigned char r, unsigned char g, unsigned char b, unsigned char a) {
  if(!info->palette) /*allocate palette if empty*/ {
    lodepng_color_mode_alloc_palette(info);
    if(!info->palette) return 83; /*alloc fail*/
  }
  if(info->palettesize >= 256) {
    return 108; /*too many palette values*/
  }
  info->palette[4 * info->palettesize + 0] = r;
  info->palette[4 * info->palettesize + 1] = g;
  info->palette[4 * info->palettesize + 2] = b;
  info->palette[4 * info->palettesize + 3] = a;
  ++info->palettesize;
  return 0;
}

/*calculate bits per pixel out of colortype and bitdepth*/
unsigned lodepng_get_bpp(const LodePNGColorMode* info) {
  return lodepng_get_bpp_lct(info->colortype, info->bitdepth);
}

unsigned lodepng_get_channels(const LodePNGColorMode* info) {
  return getNumColorChannels(info->colortype);
}

unsigned lodepng_is_greyscale_type(const LodePNGColorMode* info) {
  return info->colortype == LCT_GREY || info->colortype == LCT_GREY_ALPHA;
}

unsigned lodepng_is_alpha_type(const LodePNGColorMode* info) {
  return (info->colortype & 4) != 0; /*4 or 6*/
}

unsigned lodepng_is_palette_type(const LodePNGColorMode* info) {
  return info->colortype == LCT_PALETTE;
}

unsigned lodepng_has_palette_alpha(const LodePNGColorMode* info) {
  size_t i;
  for(i = 0; i != info->palettesize; ++i) {
    if(info->palette[i * 4 + 3] < 255) return 1;
  }
  return 0;
}

unsigned lodepng_can_have_alpha(const LodePNGColorMode* info) {
  return info->key_defined
      || lodepng_is_alpha_type(info)
      || lodepng_has_palette_alpha(info);
}

static size_t lodepng_get_raw_size_lct(unsigned w, unsigned h, LodePNGColorType colortype, unsigned bitdepth) {
  size_t bpp = lodepng_get_bpp_lct(colortype, bitdepth);
  size_t n = (size_t)w * (size_t)h;
  return ((n / 8u) * bpp) + ((n & 7u) * bpp + 7u) / 8u;
}

size_t lodepng_get_raw_size(unsigned w, unsigned h, const LodePNGColorMode* color) {
  return lodepng_get_raw_size_lct(w, h, color->colortype, color->bitdepth);
}


#ifdef LODEPNG_COMPILE_PNG

/*in an idat chunk, each scanline is a multiple of 8 bits, unlike the lodepng output buffer,
and in addition has one extra byte per line: the filter byte. So this gives a larger
result than lodepng_get_raw_size. Set h to 1 to get the size of 1 row including filter byte. */
static size_t lodepng_get_raw_size_idat(unsigned w, unsigned h, unsigned bpp) {
  /* + 1 for the filter byte, and possibly plus padding bits per line. */
  /* Ignoring casts, the expression is equal to (w * bpp + 7) / 8 + 1, but avoids overflow of w * bpp */
  size_t line = ((size_t)(w / 8u) * bpp) + 1u + ((w & 7u) * bpp + 7u) / 8u;
  return (size_t)h * line;
}
#endif /*LODEPNG_COMPILE_PNG*/

void lodepng_info_init(LodePNGInfo* info) {
  lodepng_color_mode_init(&info->color);
  info->interlace_method = 0;
  info->compression_method = 0;
  info->filter_method = 0;
}

void lodepng_info_cleanup(LodePNGInfo* info) {
  lodepng_color_mode_cleanup(&info->color);
}

unsigned lodepng_info_copy(LodePNGInfo* dest, const LodePNGInfo* source) {
  lodepng_info_cleanup(dest);
  lodepng_memcpy(dest, source, sizeof(LodePNGInfo));
  lodepng_color_mode_init(&dest->color);
  CERROR_TRY_RETURN(lodepng_color_mode_copy(&dest->color, &source->color));
  return 0;
}

/* ////////////////////////////////////////////////////////////////////////// */

/*index: bitgroup index, bits: bitgroup size(1, 2 or 4), in: bitgroup value, out: octet array to add bits to*/
static void addColorBits(unsigned char* out, size_t index, unsigned bits, unsigned in) {
  unsigned m = bits == 1 ? 7 : bits == 2 ? 3 : 1; /*8 / bits - 1*/
  /*p = the partial index in the byte, e.g. with 4 palettebits it is 0 for first half or 1 for second half*/
  unsigned p = index & m;
  in &= (1u << bits) - 1u; /*filter out any other bits of the input value*/
  in = in << (bits * (m - p));
  if(p == 0) out[index * bits / 8u] = in;
  else out[index * bits / 8u] |= in;
}

typedef struct ColorTree ColorTree;

/*
One node of a color tree
This is the data structure used to count the number of unique colors and to get a palette
index for a color. It's like an octree, but because the alpha channel is used too, each
node has 16 instead of 8 children.
*/
struct ColorTree {
  ColorTree* children[16]; /*up to 16 pointers to ColorTree of next level*/
  int index; /*the payload. Only has a meaningful value if this is in the last level*/
};

static void color_tree_init(ColorTree* tree) {
  lodepng_memset(tree->children, 0, 16 * sizeof(*tree->children));
  tree->index = -1;
}

static void color_tree_cleanup(ColorTree* tree) {
  int i;
  for(i = 0; i != 16; ++i) {
    if(tree->children[i]) {
      color_tree_cleanup(tree->children[i]);
      lodepng_free(tree->children[i]);
    }
  }
}

/*returns -1 if color not present, its index otherwise*/
static int color_tree_get(ColorTree* tree, unsigned char r, unsigned char g, unsigned char b, unsigned char a) {
  int bit = 0;
  for(bit = 0; bit < 8; ++bit) {
    int i = 8 * ((r >> bit) & 1) + 4 * ((g >> bit) & 1) + 2 * ((b >> bit) & 1) + 1 * ((a >> bit) & 1);
    if(!tree->children[i]) return -1;
    else tree = tree->children[i];
  }
  return tree ? tree->index : -1;
}

#ifdef LODEPNG_COMPILE_ENCODER
static int color_tree_has(ColorTree* tree, unsigned char r, unsigned char g, unsigned char b, unsigned char a) {
  return color_tree_get(tree, r, g, b, a) >= 0;
}
#endif /*LODEPNG_COMPILE_ENCODER*/

/*color is not allowed to already exist.
Index should be >= 0 (it's signed to be compatible with using -1 for "doesn't exist")
Returns error code, or 0 if ok*/
static unsigned color_tree_add(ColorTree* tree,
                               unsigned char r, unsigned char g, unsigned char b, unsigned char a, unsigned index) {
  int bit;
  for(bit = 0; bit < 8; ++bit) {
    int i = 8 * ((r >> bit) & 1) + 4 * ((g >> bit) & 1) + 2 * ((b >> bit) & 1) + 1 * ((a >> bit) & 1);
    if(!tree->children[i]) {
      tree->children[i] = (ColorTree*)lodepng_malloc(sizeof(ColorTree));
      if(!tree->children[i]) return 83; /*alloc fail*/
      color_tree_init(tree->children[i]);
    }
    tree = tree->children[i];
  }
  tree->index = (int)index;
  return 0;
}

/*put a pixel, given its RGBA color, into image of any color type*/
static unsigned rgba8ToPixel(unsigned char* out, size_t i,
                             const LodePNGColorMode* mode, ColorTree* tree /*for palette*/,
                             unsigned char r, unsigned char g, unsigned char b, unsigned char a) {
  if(mode->colortype == LCT_GREY) {
    unsigned char gray = r; /*((unsigned short)r + g + b) / 3u;*/
    if(mode->bitdepth == 8) out[i] = gray;
    else if(mode->bitdepth == 16) out[i * 2 + 0] = out[i * 2 + 1] = gray;
    else {
      /*take the most significant bits of gray*/
      gray = ((unsigned)gray >> (8u - mode->bitdepth)) & ((1u << mode->bitdepth) - 1u);
      addColorBits(out, i, mode->bitdepth, gray);
    }
  } else if(mode->colortype == LCT_RGB) {
    if(mode->bitdepth == 8) {
      out[i * 3 + 0] = r;
      out[i * 3 + 1] = g;
      out[i * 3 + 2] = b;
    } else {
      out[i * 6 + 0] = out[i * 6 + 1] = r;
      out[i * 6 + 2] = out[i * 6 + 3] = g;
      out[i * 6 + 4] = out[i * 6 + 5] = b;
    }
  } else if(mode->colortype == LCT_PALETTE) {
    int index = color_tree_get(tree, r, g, b, a);
    if(index < 0) return 82; /*color not in palette*/
    if(mode->bitdepth == 8) out[i] = index;
    else addColorBits(out, i, mode->bitdepth, (unsigned)index);
  } else if(mode->colortype == LCT_GREY_ALPHA) {
    unsigned char gray = r; /*((unsigned short)r + g + b) / 3u;*/
    if(mode->bitdepth == 8) {
      out[i * 2 + 0] = gray;
      out[i * 2 + 1] = a;
    } else if(mode->bitdepth == 16) {
      out[i * 4 + 0] = out[i * 4 + 1] = gray;
      out[i * 4 + 2] = out[i * 4 + 3] = a;
    }
  } else if(mode->colortype == LCT_RGBA) {
    if(mode->bitdepth == 8) {
      out[i * 4 + 0] = r;
      out[i * 4 + 1] = g;
      out[i * 4 + 2] = b;
      out[i * 4 + 3] = a;
    } else {
      out[i * 8 + 0] = out[i * 8 + 1] = r;
      out[i * 8 + 2] = out[i * 8 + 3] = g;
      out[i * 8 + 4] = out[i * 8 + 5] = b;
      out[i * 8 + 6] = out[i * 8 + 7] = a;
    }
  }

  return 0; /*no error*/
}

/*put a pixel, given its RGBA16 color, into image of any color 16-bitdepth type*/
static void rgba16ToPixel(unsigned char* out, size_t i,
                         const LodePNGColorMode* mode,
                         unsigned short r, unsigned short g, unsigned short b, unsigned short a) {
  if(mode->colortype == LCT_GREY) {
    unsigned short gray = r; /*((unsigned)r + g + b) / 3u;*/
    out[i * 2 + 0] = (gray >> 8) & 255;
    out[i * 2 + 1] = gray & 255;
  } else if(mode->colortype == LCT_RGB) {
    out[i * 6 + 0] = (r >> 8) & 255;
    out[i * 6 + 1] = r & 255;
    out[i * 6 + 2] = (g >> 8) & 255;
    out[i * 6 + 3] = g & 255;
    out[i * 6 + 4] = (b >> 8) & 255;
    out[i * 6 + 5] = b & 255;
  } else if(mode->colortype == LCT_GREY_ALPHA) {
    unsigned short gray = r; /*((unsigned)r + g + b) / 3u;*/
    out[i * 4 + 0] = (gray >> 8) & 255;
    out[i * 4 + 1] = gray & 255;
    out[i * 4 + 2] = (a >> 8) & 255;
    out[i * 4 + 3] = a & 255;
  } else if(mode->colortype == LCT_RGBA) {
    out[i * 8 + 0] = (r >> 8) & 255;
    out[i * 8 + 1] = r & 255;
    out[i * 8 + 2] = (g >> 8) & 255;
    out[i * 8 + 3] = g & 255;
    out[i * 8 + 4] = (b >> 8) & 255;
    out[i * 8 + 5] = b & 255;
    out[i * 8 + 6] = (a >> 8) & 255;
    out[i * 8 + 7] = a & 255;
  }
}

/*Get RGBA8 color of pixel with index i (y * width + x) from the raw image with given color type.*/
static void getPixelColorRGBA8(unsigned char* r, unsigned char* g,
                               unsigned char* b, unsigned char* a,
                               const unsigned char* in, size_t i,
                               const LodePNGColorMode* mode) {
  if(mode->colortype == LCT_GREY) {
    if(mode->bitdepth == 8) {
      *r = *g = *b = in[i];
      if(mode->key_defined && *r == mode->key_r) *a = 0;
      else *a = 255;
    } else if(mode->bitdepth == 16) {
      *r = *g = *b = in[i * 2 + 0];
      if(mode->key_defined && 256U * in[i * 2 + 0] + in[i * 2 + 1] == mode->key_r) *a = 0;
      else *a = 255;
    } else {
      unsigned highest = ((1U << mode->bitdepth) - 1U); /*highest possible value for this bit depth*/
      size_t j = i * mode->bitdepth;
      unsigned value = readBitsFromReversedStream(&j, in, mode->bitdepth);
      *r = *g = *b = (value * 255) / highest;
      if(mode->key_defined && value == mode->key_r) *a = 0;
      else *a = 255;
    }
  } else if(mode->colortype == LCT_RGB) {
    if(mode->bitdepth == 8) {
      *r = in[i * 3 + 0]; *g = in[i * 3 + 1]; *b = in[i * 3 + 2];
      if(mode->key_defined && *r == mode->key_r && *g == mode->key_g && *b == mode->key_b) *a = 0;
      else *a = 255;
    } else {
      *r = in[i * 6 + 0];
      *g = in[i * 6 + 2];
      *b = in[i * 6 + 4];
      if(mode->key_defined && 256U * in[i * 6 + 0] + in[i * 6 + 1] == mode->key_r
         && 256U * in[i * 6 + 2] + in[i * 6 + 3] == mode->key_g
         && 256U * in[i * 6 + 4] + in[i * 6 + 5] == mode->key_b) *a = 0;
      else *a = 255;
    }
  } else if(mode->colortype == LCT_PALETTE) {
    unsigned index;
    if(mode->bitdepth == 8) index = in[i];
    else {
      size_t j = i * mode->bitdepth;
      index = readBitsFromReversedStream(&j, in, mode->bitdepth);
    }
    /*out of bounds of palette not checked: see lodepng_color_mode_alloc_palette.*/
    *r = mode->palette[index * 4 + 0];
    *g = mode->palette[index * 4 + 1];
    *b = mode->palette[index * 4 + 2];
    *a = mode->palette[index * 4 + 3];
  } else if(mode->colortype == LCT_GREY_ALPHA) {
    if(mode->bitdepth == 8) {
      *r = *g = *b = in[i * 2 + 0];
      *a = in[i * 2 + 1];
    } else {
      *r = *g = *b = in[i * 4 + 0];
      *a = in[i * 4 + 2];
    }
  } else if(mode->colortype == LCT_RGBA) {
    if(mode->bitdepth == 8) {
      *r = in[i * 4 + 0];
      *g = in[i * 4 + 1];
      *b = in[i * 4 + 2];
      *a = in[i * 4 + 3];
    } else {
      *r = in[i * 8 + 0];
      *g = in[i * 8 + 2];
      *b = in[i * 8 + 4];
      *a = in[i * 8 + 6];
    }
  }
}

/*Similar to getPixelColorRGBA8, but with all the for loops inside of the color
mode test cases, optimized to convert the colors much faster, when converting
to the common case of RGBA with 8 bit per channel. buffer must be RGBA with
enough memory.*/
static void getPixelColorsRGBA8(unsigned char* LODEPNG_RESTRICT buffer, size_t numpixels,
                                const unsigned char* LODEPNG_RESTRICT in,
                                const LodePNGColorMode* mode) {
  unsigned num_channels = 4;
  size_t i;
  if(mode->colortype == LCT_GREY) {
    if(mode->bitdepth == 8) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = buffer[1] = buffer[2] = in[i];
        buffer[3] = 255;
      }
      if(mode->key_defined) {
        buffer -= numpixels * num_channels;
        for(i = 0; i != numpixels; ++i, buffer += num_channels) {
          if(buffer[0] == mode->key_r) buffer[3] = 0;
        }
      }
    } else if(mode->bitdepth == 16) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = buffer[1] = buffer[2] = in[i * 2];
        buffer[3] = mode->key_defined && 256U * in[i * 2 + 0] + in[i * 2 + 1] == mode->key_r ? 0 : 255;
      }
    } else {
      unsigned highest = ((1U << mode->bitdepth) - 1U); /*highest possible value for this bit depth*/
      size_t j = 0;
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        unsigned value = readBitsFromReversedStream(&j, in, mode->bitdepth);
        buffer[0] = buffer[1] = buffer[2] = (value * 255) / highest;
        buffer[3] = mode->key_defined && value == mode->key_r ? 0 : 255;
      }
    }
  } else if(mode->colortype == LCT_RGB) {
    if(mode->bitdepth == 8) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        lodepng_memcpy(buffer, &in[i * 3], 3);
        buffer[3] = 255;
      }
      if(mode->key_defined) {
        buffer -= numpixels * num_channels;
        for(i = 0; i != numpixels; ++i, buffer += num_channels) {
          if(buffer[0] == mode->key_r && buffer[1]== mode->key_g && buffer[2] == mode->key_b) buffer[3] = 0;
        }
      }
    } else {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = in[i * 6 + 0];
        buffer[1] = in[i * 6 + 2];
        buffer[2] = in[i * 6 + 4];
        buffer[3] = mode->key_defined
           && 256U * in[i * 6 + 0] + in[i * 6 + 1] == mode->key_r
           && 256U * in[i * 6 + 2] + in[i * 6 + 3] == mode->key_g
           && 256U * in[i * 6 + 4] + in[i * 6 + 5] == mode->key_b ? 0 : 255;
      }
    }
  } else if(mode->colortype == LCT_PALETTE) {
    if(mode->bitdepth == 8) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        unsigned index = in[i];
        /*out of bounds of palette not checked: see lodepng_color_mode_alloc_palette.*/
        lodepng_memcpy(buffer, &mode->palette[index * 4], 4);
      }
    } else {
      size_t j = 0;
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        unsigned index = readBitsFromReversedStream(&j, in, mode->bitdepth);
        /*out of bounds of palette not checked: see lodepng_color_mode_alloc_palette.*/
        lodepng_memcpy(buffer, &mode->palette[index * 4], 4);
      }
    }
  } else if(mode->colortype == LCT_GREY_ALPHA) {
    if(mode->bitdepth == 8) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = buffer[1] = buffer[2] = in[i * 2 + 0];
        buffer[3] = in[i * 2 + 1];
      }
    } else {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = buffer[1] = buffer[2] = in[i * 4 + 0];
        buffer[3] = in[i * 4 + 2];
      }
    }
  } else if(mode->colortype == LCT_RGBA) {
    if(mode->bitdepth == 8) {
      lodepng_memcpy(buffer, in, numpixels * 4);
    } else {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = in[i * 8 + 0];
        buffer[1] = in[i * 8 + 2];
        buffer[2] = in[i * 8 + 4];
        buffer[3] = in[i * 8 + 6];
      }
    }
  }
}

/*Similar to getPixelColorsRGBA8, but with 3-channel RGB output.*/
static void getPixelColorsRGB8(unsigned char* LODEPNG_RESTRICT buffer, size_t numpixels,
                               const unsigned char* LODEPNG_RESTRICT in,
                               const LodePNGColorMode* mode) {
  const unsigned num_channels = 3;
  size_t i;
  if(mode->colortype == LCT_GREY) {
    if(mode->bitdepth == 8) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = buffer[1] = buffer[2] = in[i];
      }
    } else if(mode->bitdepth == 16) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = buffer[1] = buffer[2] = in[i * 2];
      }
    } else {
      unsigned highest = ((1U << mode->bitdepth) - 1U); /*highest possible value for this bit depth*/
      size_t j = 0;
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        unsigned value = readBitsFromReversedStream(&j, in, mode->bitdepth);
        buffer[0] = buffer[1] = buffer[2] = (value * 255) / highest;
      }
    }
  } else if(mode->colortype == LCT_RGB) {
    if(mode->bitdepth == 8) {
      lodepng_memcpy(buffer, in, numpixels * 3);
    } else {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = in[i * 6 + 0];
        buffer[1] = in[i * 6 + 2];
        buffer[2] = in[i * 6 + 4];
      }
    }
  } else if(mode->colortype == LCT_PALETTE) {
    if(mode->bitdepth == 8) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        unsigned index = in[i];
        /*out of bounds of palette not checked: see lodepng_color_mode_alloc_palette.*/
        lodepng_memcpy(buffer, &mode->palette[index * 4], 3);
      }
    } else {
      size_t j = 0;
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        unsigned index = readBitsFromReversedStream(&j, in, mode->bitdepth);
        /*out of bounds of palette not checked: see lodepng_color_mode_alloc_palette.*/
        lodepng_memcpy(buffer, &mode->palette[index * 4], 3);
      }
    }
  } else if(mode->colortype == LCT_GREY_ALPHA) {
    if(mode->bitdepth == 8) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = buffer[1] = buffer[2] = in[i * 2 + 0];
      }
    } else {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = buffer[1] = buffer[2] = in[i * 4 + 0];
      }
    }
  } else if(mode->colortype == LCT_RGBA) {
    if(mode->bitdepth == 8) {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        lodepng_memcpy(buffer, &in[i * 4], 3);
      }
    } else {
      for(i = 0; i != numpixels; ++i, buffer += num_channels) {
        buffer[0] = in[i * 8 + 0];
        buffer[1] = in[i * 8 + 2];
        buffer[2] = in[i * 8 + 4];
      }
    }
  }
}

/*Get RGBA16 color of pixel with index i (y * width + x) from the raw image with
given color type, but the given color type must be 16-bit itself.*/
static void getPixelColorRGBA16(unsigned short* r, unsigned short* g, unsigned short* b, unsigned short* a,
                                const unsigned char* in, size_t i, const LodePNGColorMode* mode) {
  if(mode->colortype == LCT_GREY) {
    *r = *g = *b = 256 * in[i * 2 + 0] + in[i * 2 + 1];
    if(mode->key_defined && 256U * in[i * 2 + 0] + in[i * 2 + 1] == mode->key_r) *a = 0;
    else *a = 65535;
  } else if(mode->colortype == LCT_RGB) {
    *r = 256u * in[i * 6 + 0] + in[i * 6 + 1];
    *g = 256u * in[i * 6 + 2] + in[i * 6 + 3];
    *b = 256u * in[i * 6 + 4] + in[i * 6 + 5];
    if(mode->key_defined
       && 256u * in[i * 6 + 0] + in[i * 6 + 1] == mode->key_r
       && 256u * in[i * 6 + 2] + in[i * 6 + 3] == mode->key_g
       && 256u * in[i * 6 + 4] + in[i * 6 + 5] == mode->key_b) *a = 0;
    else *a = 65535;
  } else if(mode->colortype == LCT_GREY_ALPHA) {
    *r = *g = *b = 256u * in[i * 4 + 0] + in[i * 4 + 1];
    *a = 256u * in[i * 4 + 2] + in[i * 4 + 3];
  } else if(mode->colortype == LCT_RGBA) {
    *r = 256u * in[i * 8 + 0] + in[i * 8 + 1];
    *g = 256u * in[i * 8 + 2] + in[i * 8 + 3];
    *b = 256u * in[i * 8 + 4] + in[i * 8 + 5];
    *a = 256u * in[i * 8 + 6] + in[i * 8 + 7];
  }
}

unsigned lodepng_convert(unsigned char* out, const unsigned char* in,
                         const LodePNGColorMode* mode_out, const LodePNGColorMode* mode_in,
                         unsigned w, unsigned h) {
  size_t i;
  ColorTree tree;
  size_t numpixels = (size_t)w * (size_t)h;
  unsigned error = 0;

  if(mode_in->colortype == LCT_PALETTE && !mode_in->palette) {
    return 107; /* error: must provide palette if input mode is palette */
  }

  if(lodepng_color_mode_equal(mode_out, mode_in)) {
    size_t numbytes = lodepng_get_raw_size(w, h, mode_in);
    lodepng_memcpy(out, in, numbytes);
    return 0;
  }

  if(mode_out->colortype == LCT_PALETTE) {
    size_t palettesize = mode_out->palettesize;
    const unsigned char* palette = mode_out->palette;
    size_t palsize = (size_t)1u << mode_out->bitdepth;
    /*if the user specified output palette but did not give the values, assume
    they want the values of the input color type (assuming that one is palette).
    Note that we never create a new palette ourselves.*/
    if(palettesize == 0) {
      palettesize = mode_in->palettesize;
      palette = mode_in->palette;
      /*if the input was also palette with same bitdepth, then the color types are also
      equal, so copy literally. This to preserve the exact indices that were in the PNG
      even in case there are duplicate colors in the palette.*/
      if(mode_in->colortype == LCT_PALETTE && mode_in->bitdepth == mode_out->bitdepth) {
        size_t numbytes = lodepng_get_raw_size(w, h, mode_in);
        lodepng_memcpy(out, in, numbytes);
        return 0;
      }
    }
    if(palettesize < palsize) palsize = palettesize;
    color_tree_init(&tree);
    for(i = 0; i != palsize; ++i) {
      const unsigned char* p = &palette[i * 4];
      error = color_tree_add(&tree, p[0], p[1], p[2], p[3], (unsigned)i);
      if(error) break;
    }
  }

  if(!error) {
    if(mode_in->bitdepth == 16 && mode_out->bitdepth == 16) {
      for(i = 0; i != numpixels; ++i) {
        unsigned short r = 0, g = 0, b = 0, a = 0;
        getPixelColorRGBA16(&r, &g, &b, &a, in, i, mode_in);
        rgba16ToPixel(out, i, mode_out, r, g, b, a);
      }
    } else if(mode_out->bitdepth == 8 && mode_out->colortype == LCT_RGBA) {
      getPixelColorsRGBA8(out, numpixels, in, mode_in);
    } else if(mode_out->bitdepth == 8 && mode_out->colortype == LCT_RGB) {
      getPixelColorsRGB8(out, numpixels, in, mode_in);
    } else {
      unsigned char r = 0, g = 0, b = 0, a = 0;
      for(i = 0; i != numpixels; ++i) {
        getPixelColorRGBA8(&r, &g, &b, &a, in, i, mode_in);
        error = rgba8ToPixel(out, i, mode_out, &tree, r, g, b, a);
        if(error) break;
      }
    }
  }

  if(mode_out->colortype == LCT_PALETTE) {
    color_tree_cleanup(&tree);
  }

  return error;
}


/* Converts a single rgb color without alpha from one type to another, color bits truncated to
their bitdepth. In case of single channel (gray or palette), only the r channel is used. Slow
function, do not use to process all pixels of an image. Alpha channel not supported on purpose:
this is for bKGD, supporting alpha may prevent it from finding a color in the palette, from the
specification it looks like bKGD should ignore the alpha values of the palette since it can use
any palette index but doesn't have an alpha channel. Idem with ignoring color key. */
unsigned lodepng_convert_rgb(
    unsigned* r_out, unsigned* g_out, unsigned* b_out,
    unsigned r_in, unsigned g_in, unsigned b_in,
    const LodePNGColorMode* mode_out, const LodePNGColorMode* mode_in) {
  unsigned r = 0, g = 0, b = 0;
  unsigned mul = 65535 / ((1u << mode_in->bitdepth) - 1u); /*65535, 21845, 4369, 257, 1*/
  unsigned shift = 16 - mode_out->bitdepth;

  if(mode_in->colortype == LCT_GREY || mode_in->colortype == LCT_GREY_ALPHA) {
    r = g = b = r_in * mul;
  } else if(mode_in->colortype == LCT_RGB || mode_in->colortype == LCT_RGBA) {
    r = r_in * mul;
    g = g_in * mul;
    b = b_in * mul;
  } else if(mode_in->colortype == LCT_PALETTE) {
    if(r_in >= mode_in->palettesize) return 82;
    r = mode_in->palette[r_in * 4 + 0] * 257u;
    g = mode_in->palette[r_in * 4 + 1] * 257u;
    b = mode_in->palette[r_in * 4 + 2] * 257u;
  } else {
    return 31;
  }

  /* now convert to output format */
  if(mode_out->colortype == LCT_GREY || mode_out->colortype == LCT_GREY_ALPHA) {
    *r_out = r >> shift ;
  } else if(mode_out->colortype == LCT_RGB || mode_out->colortype == LCT_RGBA) {
    *r_out = r >> shift ;
    *g_out = g >> shift ;
    *b_out = b >> shift ;
  } else if(mode_out->colortype == LCT_PALETTE) {
    unsigned i;
    /* a 16-bit color cannot be in the palette */
    if((r >> 8) != (r & 255) || (g >> 8) != (g & 255) || (b >> 8) != (b & 255)) return 82;
    for(i = 0; i < mode_out->palettesize; i++) {
      unsigned j = i * 4;
      if((r >> 8) == mode_out->palette[j + 0] && (g >> 8) == mode_out->palette[j + 1] &&
          (b >> 8) == mode_out->palette[j + 2]) {
        *r_out = i;
        return 0;
      }
    }
    return 82;
  } else {
    return 31;
  }

  return 0;
}

#ifdef LODEPNG_COMPILE_ENCODER

void lodepng_color_stats_init(LodePNGColorStats* stats) {
  /*stats*/
  stats->colored = 0;
  stats->key = 0;
  stats->key_r = stats->key_g = stats->key_b = 0;
  stats->alpha = 0;
  stats->numcolors = 0;
  stats->bits = 1;
  stats->numpixels = 0;
  /*settings*/
  stats->allow_palette = 1;
  stats->allow_greyscale = 1;
}

/*function used for debug purposes with C++*/
/*void printColorStats(LodePNGColorStats* p) {
  std::cout << "colored: " << (int)p->colored << ", ";
  std::cout << "key: " << (int)p->key << ", ";
  std::cout << "key_r: " << (int)p->key_r << ", ";
  std::cout << "key_g: " << (int)p->key_g << ", ";
  std::cout << "key_b: " << (int)p->key_b << ", ";
  std::cout << "alpha: " << (int)p->alpha << ", ";
  std::cout << "numcolors: " << (int)p->numcolors << ", ";
  std::cout << "bits: " << (int)p->bits << std::endl;
}*/

/*Returns how many bits needed to represent given value (max 8 bit)*/
static unsigned getValueRequiredBits(unsigned char value) {
  if(value == 0 || value == 255) return 1;
  /*The scaling of 2-bit and 4-bit values uses multiples of 85 and 17*/
  if(value % 17 == 0) return value % 85 == 0 ? 2 : 4;
  return 8;
}

/*stats must already have been inited. */
unsigned lodepng_compute_color_stats(LodePNGColorStats* stats,
                                     const unsigned char* in, unsigned w, unsigned h,
                                     const LodePNGColorMode* mode_in) {
  size_t i;
  ColorTree tree;
  size_t numpixels = (size_t)w * (size_t)h;
  unsigned error = 0;

  /* mark things as done already if it would be impossible to have a more expensive case */
  unsigned colored_done = lodepng_is_greyscale_type(mode_in) ? 1 : 0;
  unsigned alpha_done = lodepng_can_have_alpha(mode_in) ? 0 : 1;
  unsigned numcolors_done = 0;
  unsigned bpp = lodepng_get_bpp(mode_in);
  unsigned bits_done = (stats->bits == 1 && bpp == 1) ? 1 : 0;
  unsigned sixteen = 0; /* whether the input image is 16 bit */
  unsigned maxnumcolors = 257;
  if(bpp <= 8) maxnumcolors = LODEPNG_MIN(257, stats->numcolors + (1u << bpp));

  stats->numpixels += numpixels;

  /*if palette not allowed, no need to compute numcolors*/
  if(!stats->allow_palette) numcolors_done = 1;

  color_tree_init(&tree);

  /*If the stats was already filled in from previous data, fill its palette in tree
  and mark things as done already if we know they are the most expensive case already*/
  if(stats->alpha) alpha_done = 1;
  if(stats->colored) colored_done = 1;
  if(stats->bits == 16) numcolors_done = 1;
  if(stats->bits >= bpp) bits_done = 1;
  if(stats->numcolors >= maxnumcolors) numcolors_done = 1;

  if(!numcolors_done) {
    for(i = 0; i < stats->numcolors; i++) {
      const unsigned char* color = &stats->palette[i * 4];
      error = color_tree_add(&tree, color[0], color[1], color[2], color[3], i);
      if(error) goto cleanup;
    }
  }

  /*Check if the 16-bit input is truly 16-bit*/
  if(mode_in->bitdepth == 16 && !sixteen) {
    unsigned short r = 0, g = 0, b = 0, a = 0;
    for(i = 0; i != numpixels; ++i) {
      getPixelColorRGBA16(&r, &g, &b, &a, in, i, mode_in);
      if((r & 255) != ((r >> 8) & 255) || (g & 255) != ((g >> 8) & 255) ||
         (b & 255) != ((b >> 8) & 255) || (a & 255) != ((a >> 8) & 255)) /*first and second byte differ*/ {
        stats->bits = 16;
        sixteen = 1;
        bits_done = 1;
        numcolors_done = 1; /*counting colors no longer useful, palette doesn't support 16-bit*/
        break;
      }
    }
  }

  if(sixteen) {
    unsigned short r = 0, g = 0, b = 0, a = 0;

    for(i = 0; i != numpixels; ++i) {
      getPixelColorRGBA16(&r, &g, &b, &a, in, i, mode_in);

      if(!colored_done && (r != g || r != b)) {
        stats->colored = 1;
        colored_done = 1;
      }

      if(!alpha_done) {
        unsigned matchkey = (r == stats->key_r && g == stats->key_g && b == stats->key_b);
        if(a != 65535 && (a != 0 || (stats->key && !matchkey))) {
          stats->alpha = 1;
          stats->key = 0;
          alpha_done = 1;
        } else if(a == 0 && !stats->alpha && !stats->key) {
          stats->key = 1;
          stats->key_r = r;
          stats->key_g = g;
          stats->key_b = b;
        } else if(a == 65535 && stats->key && matchkey) {
          /* Color key cannot be used if an opaque pixel also has that RGB color. */
          stats->alpha = 1;
          stats->key = 0;
          alpha_done = 1;
        }
      }
      if(alpha_done && numcolors_done && colored_done && bits_done) break;
    }

    if(stats->key && !stats->alpha) {
      for(i = 0; i != numpixels; ++i) {
        getPixelColorRGBA16(&r, &g, &b, &a, in, i, mode_in);
        if(a != 0 && r == stats->key_r && g == stats->key_g && b == stats->key_b) {
          /* Color key cannot be used if an opaque pixel also has that RGB color. */
          stats->alpha = 1;
          stats->key = 0;
          alpha_done = 1;
        }
      }
    }
  } else /* < 16-bit */ {
    unsigned char r = 0, g = 0, b = 0, a = 0;
    for(i = 0; i != numpixels; ++i) {
      getPixelColorRGBA8(&r, &g, &b, &a, in, i, mode_in);

      if(!bits_done && stats->bits < 8) {
        /*only r is checked, < 8 bits is only relevant for grayscale*/
        unsigned bits = getValueRequiredBits(r);
        if(bits > stats->bits) stats->bits = bits;
      }
      bits_done = (stats->bits >= bpp);

      if(!colored_done && (r != g || r != b)) {
        stats->colored = 1;
        colored_done = 1;
        if(stats->bits < 8) stats->bits = 8; /*PNG has no colored modes with less than 8-bit per channel*/
      }

      if(!alpha_done) {
        unsigned matchkey = (r == stats->key_r && g == stats->key_g && b == stats->key_b);
        if(a != 255 && (a != 0 || (stats->key && !matchkey))) {
          stats->alpha = 1;
          stats->key = 0;
          alpha_done = 1;
          if(stats->bits < 8) stats->bits = 8; /*PNG has no alphachannel modes with less than 8-bit per channel*/
        } else if(a == 0 && !stats->alpha && !stats->key) {
          stats->key = 1;
          stats->key_r = r;
          stats->key_g = g;
          stats->key_b = b;
        } else if(a == 255 && stats->key && matchkey) {
          /* Color key cannot be used if an opaque pixel also has that RGB color. */
          stats->alpha = 1;
          stats->key = 0;
          alpha_done = 1;
          if(stats->bits < 8) stats->bits = 8; /*PNG has no alphachannel modes with less than 8-bit per channel*/
        }
      }

      if(!numcolors_done) {
        if(!color_tree_has(&tree, r, g, b, a)) {
          error = color_tree_add(&tree, r, g, b, a, stats->numcolors);
          if(error) goto cleanup;
          if(stats->numcolors < 256) {
            unsigned char* p = stats->palette;
            unsigned n = stats->numcolors;
            p[n * 4 + 0] = r;
            p[n * 4 + 1] = g;
            p[n * 4 + 2] = b;
            p[n * 4 + 3] = a;
          }
          ++stats->numcolors;
          numcolors_done = stats->numcolors >= maxnumcolors;
        }
      }

      if(alpha_done && numcolors_done && colored_done && bits_done) break;
    }

    if(stats->key && !stats->alpha) {
      for(i = 0; i != numpixels; ++i) {
        getPixelColorRGBA8(&r, &g, &b, &a, in, i, mode_in);
        if(a != 0 && r == stats->key_r && g == stats->key_g && b == stats->key_b) {
          /* Color key cannot be used if an opaque pixel also has that RGB color. */
          stats->alpha = 1;
          stats->key = 0;
          alpha_done = 1;
          if(stats->bits < 8) stats->bits = 8; /*PNG has no alphachannel modes with less than 8-bit per channel*/
        }
      }
    }

    /*make the stats's key always 16-bit for consistency - repeat each byte twice*/
    stats->key_r += (stats->key_r << 8);
    stats->key_g += (stats->key_g << 8);
    stats->key_b += (stats->key_b << 8);
  }

cleanup:
  color_tree_cleanup(&tree);
  return error;
}

/*Computes a minimal PNG color model that can contain all colors as indicated by the stats.
The stats should be computed with lodepng_compute_color_stats.
mode_in is raw color profile of the image the stats were computed on, to copy palette order from when relevant.
Minimal PNG color model means the color type and bit depth that gives smallest amount of bits in the output image,
e.g. gray if only grayscale pixels, palette if less than 256 colors, color key if only single transparent color, ...
This is used if auto_convert is enabled (it is by default).
*/
static unsigned auto_choose_color(LodePNGColorMode* mode_out,
                                  const LodePNGColorMode* mode_in,
                                  const LodePNGColorStats* stats) {
  unsigned error = 0;
  unsigned palettebits;
  size_t i, n;
  size_t numpixels = stats->numpixels;
  unsigned palette_ok, gray_ok;

  unsigned alpha = stats->alpha;
  unsigned key = stats->key;
  unsigned bits = stats->bits;

  mode_out->key_defined = 0;

  if(key && numpixels <= 16) {
    alpha = 1; /*too few pixels to justify tRNS chunk overhead*/
    key = 0;
    if(bits < 8) bits = 8; /*PNG has no alphachannel modes with less than 8-bit per channel*/
  }

  gray_ok = !stats->colored;
  if(!stats->allow_greyscale) gray_ok = 0;
  if(!gray_ok && bits < 8) bits = 8;

  n = stats->numcolors;
  palettebits = n <= 2 ? 1 : (n <= 4 ? 2 : (n <= 16 ? 4 : 8));
  palette_ok = n <= 256 && bits <= 8 && n != 0; /*n==0 means likely numcolors wasn't computed*/
  if(numpixels < n * 2) palette_ok = 0; /*don't add palette overhead if image has only a few pixels*/
  if(gray_ok && !alpha && bits <= palettebits) palette_ok = 0; /*gray is less overhead*/
  if(!stats->allow_palette) palette_ok = 0;

  if(palette_ok) {
    const unsigned char* p = stats->palette;
    lodepng_palette_clear(mode_out); /*remove potential earlier palette*/
    for(i = 0; i != stats->numcolors; ++i) {
      error = lodepng_palette_add(mode_out, p[i * 4 + 0], p[i * 4 + 1], p[i * 4 + 2], p[i * 4 + 3]);
      if(error) break;
    }

    mode_out->colortype = LCT_PALETTE;
    mode_out->bitdepth = palettebits;

    if(mode_in->colortype == LCT_PALETTE && mode_in->palettesize >= mode_out->palettesize
        && mode_in->bitdepth == mode_out->bitdepth) {
      /*If input should have same palette colors, keep original to preserve its order and prevent conversion*/
      lodepng_color_mode_cleanup(mode_out);
      lodepng_color_mode_copy(mode_out, mode_in);
    }
  } else /*8-bit or 16-bit per channel*/ {
    mode_out->bitdepth = bits;
    mode_out->colortype = alpha ? (gray_ok ? LCT_GREY_ALPHA : LCT_RGBA)
                                : (gray_ok ? LCT_GREY : LCT_RGB);
    if(key) {
      unsigned mask = (1u << mode_out->bitdepth) - 1u; /*stats always uses 16-bit, mask converts it*/
      mode_out->key_r = stats->key_r & mask;
      mode_out->key_g = stats->key_g & mask;
      mode_out->key_b = stats->key_b & mask;
      mode_out->key_defined = 1;
    }
  }

  return error;
}

#endif /* #ifdef LODEPNG_COMPILE_ENCODER */

/*
Paeth predictor, used by PNG filter type 4
The parameters are of type short, but should come from unsigned chars, the shorts
are only needed to make the paeth calculation correct.
*/
static unsigned char paethPredictor(short a, short b, short c) {
  short pa = LODEPNG_ABS(b - c);
  short pb = LODEPNG_ABS(a - c);
  short pc = LODEPNG_ABS(a + b - c - c);
  /* return input value associated with smallest of pa, pb, pc (with certain priority if equal) */
  if(pb < pa) { a = b; pa = pb; }
  return (pc < pa) ? c : a;
}

/*shared values used by multiple Adam7 related functions*/

static const unsigned ADAM7_IX[7] = { 0, 4, 0, 2, 0, 1, 0 }; /*x start values*/
static const unsigned ADAM7_IY[7] = { 0, 0, 4, 0, 2, 0, 1 }; /*y start values*/
static const unsigned ADAM7_DX[7] = { 8, 8, 4, 4, 2, 2, 1 }; /*x delta values*/
static const unsigned ADAM7_DY[7] = { 8, 8, 8, 4, 4, 2, 2 }; /*y delta values*/

/*
Outputs various dimensions and positions in the image related to the Adam7 reduced images.
passw: output containing the width of the 7 passes
passh: output containing the height of the 7 passes
filter_passstart: output containing the index of the start and end of each
 reduced image with filter bytes
padded_passstart output containing the index of the start and end of each
 reduced image when without filter bytes but with padded scanlines
passstart: output containing the index of the start and end of each reduced
 image without padding between scanlines, but still padding between the images
w, h: width and height of non-interlaced image
bpp: bits per pixel
"padded" is only relevant if bpp is less than 8 and a scanline or image does not
 end at a full byte
*/
static void Adam7_getpassvalues(unsigned passw[7], unsigned passh[7], size_t filter_passstart[8],
                                size_t padded_passstart[8], size_t passstart[8], unsigned w, unsigned h, unsigned bpp) {
  /*the passstart values have 8 values: the 8th one indicates the byte after the end of the 7th (= last) pass*/
  unsigned i;

  /*calculate width and height in pixels of each pass*/
  for(i = 0; i != 7; ++i) {
    passw[i] = (w + ADAM7_DX[i] - ADAM7_IX[i] - 1) / ADAM7_DX[i];
    passh[i] = (h + ADAM7_DY[i] - ADAM7_IY[i] - 1) / ADAM7_DY[i];
    if(passw[i] == 0) passh[i] = 0;
    if(passh[i] == 0) passw[i] = 0;
  }

  filter_passstart[0] = padded_passstart[0] = passstart[0] = 0;
  for(i = 0; i != 7; ++i) {
    /*if passw[i] is 0, it's 0 bytes, not 1 (no filtertype-byte)*/
    filter_passstart[i + 1] = filter_passstart[i]
                            + ((passw[i] && passh[i]) ? passh[i] * (1u + (passw[i] * bpp + 7u) / 8u) : 0);
    /*bits padded if needed to fill full byte at end of each scanline*/
    padded_passstart[i + 1] = padded_passstart[i] + passh[i] * ((passw[i] * bpp + 7u) / 8u);
    /*only padded at end of reduced image*/
    passstart[i + 1] = passstart[i] + (passh[i] * passw[i] * bpp + 7u) / 8u;
  }
}

#ifdef LODEPNG_COMPILE_ENCODER

void lodepng_state_init(LodePNGState* state) {
#ifdef LODEPNG_COMPILE_ENCODER
  lodepng_encoder_settings_init(&state->encoder);
#endif /*LODEPNG_COMPILE_ENCODER*/
  lodepng_color_mode_init(&state->info_raw);
  lodepng_info_init(&state->info_png);
  state->error = 1;
}

void lodepng_state_cleanup(LodePNGState* state) {
  lodepng_color_mode_cleanup(&state->info_raw);
  lodepng_info_cleanup(&state->info_png);
}

void lodepng_state_copy(LodePNGState* dest, const LodePNGState* source) {
  lodepng_state_cleanup(dest);
  *dest = *source;
  lodepng_color_mode_init(&dest->info_raw);
  lodepng_info_init(&dest->info_png);
  dest->error = lodepng_color_mode_copy(&dest->info_raw, &source->info_raw); if(dest->error) return;
  dest->error = lodepng_info_copy(&dest->info_png, &source->info_png); if(dest->error) return;
}

#endif /*LODEPNG_COMPILE_ENCODER*/

#ifdef LODEPNG_COMPILE_ENCODER

/* ////////////////////////////////////////////////////////////////////////// */
/* / PNG Encoder                                                            / */
/* ////////////////////////////////////////////////////////////////////////// */


static unsigned writeSignature(ucvector* out) {
  size_t pos = out->size;
  const unsigned char signature[] = {137, 80, 78, 71, 13, 10, 26, 10};
  /*8 bytes PNG signature, aka the magic bytes*/
  if(!ucvector_resize(out, out->size + 8)) return 83; /*alloc fail*/
  lodepng_memcpy(out->data + pos, signature, 8);
  return 0;
}

static unsigned addChunk_IHDR(ucvector* out, unsigned w, unsigned h,
                              LodePNGColorType colortype, unsigned bitdepth, unsigned interlace_method) {
  unsigned char *chunk, *data;
  CERROR_TRY_RETURN(lodepng_chunk_init(&chunk, out, 13, "IHDR"));
  data = chunk + 8;

  lodepng_set32bitInt(data + 0, w); /*width*/
  lodepng_set32bitInt(data + 4, h); /*height*/
  data[8] = (unsigned char)bitdepth; /*bit depth*/
  data[9] = (unsigned char)colortype; /*color type*/
  data[10] = 0; /*compression method*/
  data[11] = 0; /*filter method*/
  data[12] = interlace_method; /*interlace method*/

  lodepng_chunk_generate_crc(chunk);
  return 0;
}

/* only adds the chunk if needed (there is a key or palette with alpha) */
static unsigned addChunk_PLTE(ucvector* out, const LodePNGColorMode* info) {
  unsigned char* chunk;
  size_t i, j = 8;

  CERROR_TRY_RETURN(lodepng_chunk_init(&chunk, out, info->palettesize * 3, "PLTE"));

  for(i = 0; i != info->palettesize; ++i) {
    /*add all channels except alpha channel*/
    chunk[j++] = info->palette[i * 4 + 0];
    chunk[j++] = info->palette[i * 4 + 1];
    chunk[j++] = info->palette[i * 4 + 2];
  }

  lodepng_chunk_generate_crc(chunk);
  return 0;
}

static unsigned addChunk_tRNS(ucvector* out, const LodePNGColorMode* info) {
  unsigned char* chunk = 0;

  if(info->colortype == LCT_PALETTE) {
    size_t i, amount = info->palettesize;
    /*the tail of palette values that all have 255 as alpha, does not have to be encoded*/
    for(i = info->palettesize; i != 0; --i) {
      if(info->palette[4 * (i - 1) + 3] != 255) break;
      --amount;
    }
    if(amount) {
      CERROR_TRY_RETURN(lodepng_chunk_init(&chunk, out, amount, "tRNS"));
      /*add the alpha channel values from the palette*/
      for(i = 0; i != amount; ++i) chunk[8 + i] = info->palette[4 * i + 3];
    }
  } else if(info->colortype == LCT_GREY) {
    if(info->key_defined) {
      CERROR_TRY_RETURN(lodepng_chunk_init(&chunk, out, 2, "tRNS"));
      chunk[8] = (unsigned char)(info->key_r >> 8);
      chunk[9] = (unsigned char)(info->key_r & 255);
    }
  } else if(info->colortype == LCT_RGB) {
    if(info->key_defined) {
      CERROR_TRY_RETURN(lodepng_chunk_init(&chunk, out, 6, "tRNS"));
      chunk[8] = (unsigned char)(info->key_r >> 8);
      chunk[9] = (unsigned char)(info->key_r & 255);
      chunk[10] = (unsigned char)(info->key_g >> 8);
      chunk[11] = (unsigned char)(info->key_g & 255);
      chunk[12] = (unsigned char)(info->key_b >> 8);
      chunk[13] = (unsigned char)(info->key_b & 255);
    }
  }

  if(chunk) lodepng_chunk_generate_crc(chunk);
  return 0;
}

static unsigned addChunk_IDAT(ucvector* out, const unsigned char* data, size_t datasize,
                              LodePNGCompressSettings* zlibsettings) {
  unsigned error = 0;
  unsigned char* zlib = 0;
  size_t zlibsize = 0;

  error = zlib_compress(&zlib, &zlibsize, data, datasize, zlibsettings);

  //Divide zlib data in multiple IDAT chunks if necessary
  if(!error) {
    if (zlibsize <= IDAT_buffer_size + 6) { //All the data fits in one IDAT chunk
      error = lodepng_chunk_createv(out, zlibsize, "IDAT", zlib);
    } else {
      size_t i;
      unsigned first = 1;
      size_t chunksize;
      for (i = 0; i < zlibsize; i += chunksize) { //Split the data into multiple IDAT chunks
        if (first) { //First chunk
          chunksize = IDAT_buffer_size + 2;
          first = 0;
        } else if (zlibsize - i <= IDAT_buffer_size + 4) { //Last chunk
          chunksize = zlibsize - i;
        } else { //Middle chunk
          chunksize = IDAT_buffer_size;
        }
        error = lodepng_chunk_createv(out, chunksize, "IDAT", zlib + i);
        if (error) break;
      }
    }
  }
  
  lodepng_free(zlib);
  return error;
}

static unsigned addChunk_IEND(ucvector* out) {
  return lodepng_chunk_createv(out, 0, "IEND", 0);
}

static void filterScanline(unsigned char* out, const unsigned char* scanline, const unsigned char* prevline,
                           size_t length, size_t bytewidth, unsigned char filterType) {
  size_t i;
  switch(filterType) {
    case 0: /*None*/
      for(i = 0; i != length; ++i) out[i] = scanline[i];
      break;
    case 1: /*Sub*/
      for(i = 0; i != bytewidth; ++i) out[i] = scanline[i];
      for(i = bytewidth; i < length; ++i) out[i] = scanline[i] - scanline[i - bytewidth];
      break;
    case 2: /*Up*/
      if(prevline) {
        for(i = 0; i != length; ++i) out[i] = scanline[i] - prevline[i];
      } else {
        for(i = 0; i != length; ++i) out[i] = scanline[i];
      }
      break;
    case 3: /*Average*/
      if(prevline) {
        for(i = 0; i != bytewidth; ++i) out[i] = scanline[i] - (prevline[i] >> 1);
        for(i = bytewidth; i < length; ++i) out[i] = scanline[i] - ((scanline[i - bytewidth] + prevline[i]) >> 1);
      } else {
        for(i = 0; i != bytewidth; ++i) out[i] = scanline[i];
        for(i = bytewidth; i < length; ++i) out[i] = scanline[i] - (scanline[i - bytewidth] >> 1);
      }
      break;
    case 4: /*Paeth*/
      if(prevline) {
        /*paethPredictor(0, prevline[i], 0) is always prevline[i]*/
        for(i = 0; i != bytewidth; ++i) out[i] = (scanline[i] - prevline[i]);
        for(i = bytewidth; i < length; ++i) {
          out[i] = (scanline[i] - paethPredictor(scanline[i - bytewidth], prevline[i], prevline[i - bytewidth]));
        }
      } else {
        for(i = 0; i != bytewidth; ++i) out[i] = scanline[i];
        /*paethPredictor(scanline[i - bytewidth], 0, 0) is always scanline[i - bytewidth]*/
        for(i = bytewidth; i < length; ++i) out[i] = (scanline[i] - scanline[i - bytewidth]);
      }
      break;
    default: return; /*invalid filter type given*/
  }
}

/* integer binary logarithm, max return value is 31 */
static size_t ilog2(size_t i) {
  size_t result = 0;
  if(i >= 65536) { result += 16; i >>= 16; }
  if(i >= 256) { result += 8; i >>= 8; }
  if(i >= 16) { result += 4; i >>= 4; }
  if(i >= 4) { result += 2; i >>= 2; }
  if(i >= 2) { result += 1; /*i >>= 1;*/ }
  return result;
}

/* integer approximation for i * log2(i), helper function for LFS_ENTROPY */
static size_t ilog2i(size_t i) {
  size_t l;
  if(i == 0) return 0;
  l = ilog2(i);
  /* approximate i*log2(i): l is integer logarithm, ((i - (1u << l)) << 1u)
  linearly approximates the missing fractional part multiplied by i */
  return i * l + ((i - (1u << l)) << 1u);
}

static unsigned filter(unsigned char* out, const unsigned char* in, unsigned w, unsigned h,
                       const LodePNGColorMode* color, const LodePNGEncoderSettings* settings) {
  /*
  For PNG filter method 0
  out must be a buffer with as size: h + (w * h * bpp + 7u) / 8u, because there are
  the scanlines with 1 extra byte per scanline
  */

  unsigned bpp = lodepng_get_bpp(color);
  /*the width of a scanline in bytes, not including the filter type*/
  size_t linebytes = lodepng_get_raw_size_idat(w, 1, bpp) - 1u;

  /*bytewidth is used for filtering, is 1 when bpp < 8, number of bytes per pixel otherwise*/
  size_t bytewidth = (bpp + 7u) / 8u;
  const unsigned char* prevline = 0;
  unsigned x, y;
  unsigned error = 0;

  if(bpp == 0) return 31; /*error: invalid color type*/
  
   /*adaptive filtering*/
   unsigned char* attempt[5]; /*five filtering attempts, one for each filter type*/
   size_t smallest = 0;
   unsigned char type, bestType = 0;

   for(type = 0; type != 5; ++type) {
      attempt[type] = (unsigned char*)lodepng_malloc(linebytes);
      if(!attempt[type]) error = 83; /*alloc fail*/
   }

   if(!error) {
      for(y = 0; y != h; ++y) {
        /*try the 4 filter types*/
        for(type = 1; type != 5; ++type) {
          size_t sum = 0;
          filterScanline(attempt[type], &in[y * linebytes], prevline, linebytes, bytewidth, type);

          /*calculate the sum of the result*/
          for(x = 0; x != linebytes; ++x) {
            /*For differences, each byte should be treated as signed, values above 127 are negative
            (converted to signed char). Filtertype 0 isn't a difference though, so use unsigned there.
            This means filtertype 0 is almost never chosen, but that is justified.*/
            unsigned char s = attempt[type][x];
            sum += s < 128 ? s : (255U - s);
          }

          /*check if this is smallest sum (or if type == 0 it's the first case so always store the values)*/
          if(type == 1 || sum < smallest) {
            bestType = type;
            smallest = sum;
          }
        }

        prevline = &in[y * linebytes];

        /*now fill the out values*/
        out[y * (linebytes + 1)] = bestType; /*the first byte of a scanline will be the filter type*/
        for(x = 0; x != linebytes; ++x) out[y * (linebytes + 1) + 1 + x] = attempt[bestType][x];
      }
   }

   for(type = 0; type != 5; ++type) lodepng_free(attempt[type]);

  return error;
}

static void addPaddingBits(unsigned char* out, const unsigned char* in,
                           size_t olinebits, size_t ilinebits, unsigned h) {
  /*The opposite of the removePaddingBits function
  olinebits must be >= ilinebits*/
  unsigned y;
  size_t diff = olinebits - ilinebits;
  size_t obp = 0, ibp = 0; /*bit pointers*/
  for(y = 0; y != h; ++y) {
    size_t x;
    for(x = 0; x < ilinebits; ++x) {
      unsigned char bit = readBitFromReversedStream(&ibp, in);
      setBitOfReversedStream(&obp, out, bit);
    }
    /*obp += diff; --> no, fill in some value in the padding bits too, to avoid
    "Use of uninitialised value of size ###" warning from valgrind*/
    for(x = 0; x != diff; ++x) setBitOfReversedStream(&obp, out, 0);
  }
}

/*
in: non-interlaced image with size w*h
out: the same pixels, but re-ordered according to PNG's Adam7 interlacing, with
 no padding bits between scanlines, but between reduced images so that each
 reduced image starts at a byte.
bpp: bits per pixel
there are no padding bits, not between scanlines, not between reduced images
in has the following size in bits: w * h * bpp.
out is possibly bigger due to padding bits between reduced images
NOTE: comments about padding bits are only relevant if bpp < 8
*/
static void Adam7_interlace(unsigned char* out, const unsigned char* in, unsigned w, unsigned h, unsigned bpp) {
  unsigned passw[7], passh[7];
  size_t filter_passstart[8], padded_passstart[8], passstart[8];
  unsigned i;

  Adam7_getpassvalues(passw, passh, filter_passstart, padded_passstart, passstart, w, h, bpp);

  if(bpp >= 8) {
    for(i = 0; i != 7; ++i) {
      unsigned x, y, b;
      size_t bytewidth = bpp / 8u;
      for(y = 0; y < passh[i]; ++y)
      for(x = 0; x < passw[i]; ++x) {
        size_t pixelinstart = ((ADAM7_IY[i] + y * ADAM7_DY[i]) * w + ADAM7_IX[i] + x * ADAM7_DX[i]) * bytewidth;
        size_t pixeloutstart = passstart[i] + (y * passw[i] + x) * bytewidth;
        for(b = 0; b < bytewidth; ++b) {
          out[pixeloutstart + b] = in[pixelinstart + b];
        }
      }
    }
  } else /*bpp < 8: Adam7 with pixels < 8 bit is a bit trickier: with bit pointers*/ {
    for(i = 0; i != 7; ++i) {
      unsigned x, y, b;
      unsigned ilinebits = bpp * passw[i];
      unsigned olinebits = bpp * w;
      size_t obp, ibp; /*bit pointers (for out and in buffer)*/
      for(y = 0; y < passh[i]; ++y)
      for(x = 0; x < passw[i]; ++x) {
        ibp = (ADAM7_IY[i] + y * ADAM7_DY[i]) * olinebits + (ADAM7_IX[i] + x * ADAM7_DX[i]) * bpp;
        obp = (8 * passstart[i]) + (y * ilinebits + x * bpp);
        for(b = 0; b < bpp; ++b) {
          unsigned char bit = readBitFromReversedStream(&ibp, in);
          setBitOfReversedStream(&obp, out, bit);
        }
      }
    }
  }
}

/*out must be buffer big enough to contain uncompressed IDAT chunk data, and in must contain the full image.
return value is error**/
static unsigned preProcessScanlines(unsigned char** out, size_t* outsize, const unsigned char* in,
                                    unsigned w, unsigned h,
                                    const LodePNGInfo* info_png, const LodePNGEncoderSettings* settings) {
  /*
  This function converts the pure 2D image with the PNG's colortype, into filtered-padded-interlaced data. Steps:
  *) if no Adam7: 1) add padding bits (= possible extra bits per scanline if bpp < 8) 2) filter
  *) if adam7: 1) Adam7_interlace 2) 7x add padding bits 3) 7x filter
  */
  unsigned bpp = lodepng_get_bpp(&info_png->color);
  unsigned error = 0;

  *outsize = h + (h * ((w * bpp + 7u) / 8u)); /*image size plus an extra byte per scanline + possible padding bits*/
  *out = (unsigned char*)lodepng_malloc(*outsize);
  if(!(*out) && (*outsize)) error = 83; /*alloc fail*/

  if(!error) {
    /*non multiple of 8 bits per scanline, padding bits needed per scanline*/
    if(bpp < 8 && w * bpp != ((w * bpp + 7u) / 8u) * 8u) {
      unsigned char* padded = (unsigned char*)lodepng_malloc(h * ((w * bpp + 7u) / 8u));
      if(!padded) error = 83; /*alloc fail*/
      if(!error) {
        addPaddingBits(padded, in, ((w * bpp + 7u) / 8u) * 8u, w * bpp, h);
        error = filter(*out, padded, w, h, &info_png->color, settings);
      }
      lodepng_free(padded);
    } else {
      /*we can immediately filter into the out buffer, no other steps needed*/
      error = filter(*out, in, w, h, &info_png->color, settings);
    }
  }

  return error;
}

unsigned lodepng_encode(unsigned char** out, size_t* outsize,
                        const unsigned char* image, unsigned w, unsigned h,
                        LodePNGState* state) {
  unsigned char* data = 0; /*uncompressed version of the IDAT chunk data*/
  size_t datasize = 0;
  ucvector outv = ucvector_init(NULL, 0);
  LodePNGInfo info;
  const LodePNGInfo* info_png = &state->info_png;

  lodepng_info_init(&info);

  /*provide some proper output values if error will happen*/
  *out = 0;
  *outsize = 0;
  state->error = 0;

  /*check input values validity*/
  if((info_png->color.colortype == LCT_PALETTE || state->encoder.force_palette)
      && (info_png->color.palettesize == 0 || info_png->color.palettesize > 256)) {
    state->error = 68; /*invalid palette size, it is only allowed to be 1-256*/
    goto cleanup;
  }
  if(state->encoder.zlibsettings.btype != 1) {
    state->error = 61; /*error: invalid btype*/
    goto cleanup;
  }
  if(info_png->interlace_method > 1) {
    state->error = 71; /*error: invalid interlace mode*/
    goto cleanup;
  }
  state->error = checkColorValidity(info_png->color.colortype, info_png->color.bitdepth);
  if(state->error) goto cleanup; /*error: invalid color type given*/
  state->error = checkColorValidity(state->info_raw.colortype, state->info_raw.bitdepth);
  if(state->error) goto cleanup; /*error: invalid color type given*/

  /* color convert and compute scanline filter types */
  lodepng_info_copy(&info, &state->info_png);
  
  preProcessScanlines(&data, &datasize, image, w, h, &info, &state->encoder);
  
  /*write signature and chunks*/
   state->error = writeSignature(&outv);
   if(state->error) goto cleanup;
   /*IHDR*/
   state->error = addChunk_IHDR(&outv, w, h, info.color.colortype, info.color.bitdepth, info.interlace_method);
   if(state->error) goto cleanup;
   /*PLTE*/
   if(info.color.colortype == LCT_PALETTE) {
      state->error = addChunk_PLTE(&outv, &info.color);
      if(state->error) goto cleanup;
   }
   /*IDAT (multiple IDAT chunks must be consecutive)*/
   state->error = addChunk_IDAT(&outv, data, datasize, &state->encoder.zlibsettings);
   if(state->error) goto cleanup;
   state->error = addChunk_IEND(&outv);
   if(state->error) goto cleanup;

cleanup:
  lodepng_info_cleanup(&info);
  lodepng_free(data);

  /*instead of cleaning the vector up, give it to the output*/
  *out = outv.data;
  *outsize = outv.size;

  return state->error;
}

unsigned lodepng_encode_memory(unsigned char** out, size_t* outsize, const unsigned char* image,
                               unsigned w, unsigned h, LodePNGColorType colortype, unsigned bitdepth,
                               unsigned windowsize) {
  unsigned error;
  LodePNGState state;
  lodepng_state_init(&state);
  state.info_raw.colortype = colortype;
  state.info_raw.bitdepth = bitdepth;
  state.info_png.color.colortype = colortype;
  state.info_png.color.bitdepth = bitdepth;
  state.encoder.zlibsettings.windowsize = windowsize;
  lodepng_encode(out, outsize, image, w, h, &state);
  error = state.error;
  lodepng_state_cleanup(&state);
  return error;
}

#ifdef LODEPNG_COMPILE_DISK
unsigned lodepng_encode_file(const char* filename, const unsigned char* image, unsigned w, unsigned h,
                             LodePNGColorType colortype, unsigned bitdepth, unsigned windowsize) {
  unsigned char* buffer;
  size_t buffersize;
  unsigned error = lodepng_encode_memory(&buffer, &buffersize, image, w, h, colortype, bitdepth, windowsize);
  if(!error) error = lodepng_save_file(buffer, buffersize, filename);
  lodepng_free(buffer);
  return error;
}
#endif /*LODEPNG_COMPILE_DISK*/

void lodepng_encoder_settings_init(LodePNGEncoderSettings* settings) {
  lodepng_compress_settings_init(&settings->zlibsettings);
  settings->filter_palette_zero = 1;
  settings->filter_strategy = LFS_MINSUM;
  settings->auto_convert = 0;
  settings->force_palette = 0;
  settings->predefined_filters = 0;
}

#endif /*LODEPNG_COMPILE_ENCODER*/
#endif /*LODEPNG_COMPILE_PNG*/

#ifdef LODEPNG_COMPILE_ERROR_TEXT
/*
This returns the description of a numerical error code in English. This is also
the documentation of all the error codes.
*/
const char* lodepng_error_text(unsigned code) {
  switch(code) {
    case 0: return "no error, everything went ok";
    case 1: return "nothing done yet"; /*the Encoder/Decoder has done nothing yet, error checking makes no sense yet*/
    case 10: return "end of input memory reached without huffman end code"; /*while huffman decoding*/
    case 11: return "error in code tree made it jump outside of huffman tree"; /*while huffman decoding*/
    case 13: return "problem while processing dynamic deflate block";
    case 14: return "problem while processing dynamic deflate block";
    case 15: return "problem while processing dynamic deflate block";
    /*this error could happen if there are only 0 or 1 symbols present in the huffman code:*/
    case 16: return "invalid code while processing dynamic deflate block";
    case 17: return "end of out buffer memory reached while inflating";
    case 18: return "invalid distance code while inflating";
    case 19: return "end of out buffer memory reached while inflating";
    case 20: return "invalid deflate block BTYPE encountered while decoding";
    case 21: return "NLEN is not ones complement of LEN in a deflate block";

    /*end of out buffer memory reached while inflating:
    This can happen if the inflated deflate data is longer than the amount of bytes required to fill up
    all the pixels of the image, given the color depth and image dimensions. Something that doesn't
    happen in a normal, well encoded, PNG image.*/
    case 22: return "end of out buffer memory reached while inflating";
    case 23: return "end of in buffer memory reached while inflating";
    case 24: return "invalid FCHECK in zlib header";
    case 25: return "invalid compression method in zlib header";
    case 26: return "FDICT encountered in zlib header while it's not used for PNG";
    case 27: return "PNG file is smaller than a PNG header";
    /*Checks the magic file header, the first 8 bytes of the PNG file*/
    case 28: return "incorrect PNG signature, it's no PNG or corrupted";
    case 29: return "first chunk is not the header chunk";
    case 30: return "chunk length too large, chunk broken off at end of file";
    case 31: return "illegal PNG color type or bpp";
    case 32: return "illegal PNG compression method";
    case 33: return "illegal PNG filter method";
    case 34: return "illegal PNG interlace method";
    case 35: return "chunk length of a chunk is too large or the chunk too small";
    case 36: return "illegal PNG filter type encountered";
    case 37: return "illegal bit depth for this color type given";
    case 38: return "the palette is too small or too big"; /*0, or more than 256 colors*/
    case 39: return "tRNS chunk before PLTE or has more entries than palette size";
    case 40: return "tRNS chunk has wrong size for grayscale image";
    case 41: return "tRNS chunk has wrong size for RGB image";
    case 42: return "tRNS chunk appeared while it was not allowed for this color type";
    case 43: return "bKGD chunk has wrong size for palette image";
    case 44: return "bKGD chunk has wrong size for grayscale image";
    case 45: return "bKGD chunk has wrong size for RGB image";
    case 48: return "empty input buffer given to decoder. Maybe caused by non-existing file?";
    case 49: return "jumped past memory while generating dynamic huffman tree";
    case 50: return "jumped past memory while generating dynamic huffman tree";
    case 51: return "jumped past memory while inflating huffman block";
    case 52: return "jumped past memory while inflating";
    case 53: return "size of zlib data too small";
    case 54: return "repeat symbol in tree while there was no value symbol yet";
    /*jumped past tree while generating huffman tree, this could be when the
    tree will have more leaves than symbols after generating it out of the
    given lengths. They call this an oversubscribed dynamic bit lengths tree in zlib.*/
    case 55: return "jumped past tree while generating huffman tree";
    case 56: return "given output image colortype or bitdepth not supported for color conversion";
    case 57: return "invalid CRC encountered (checking CRC can be disabled)";
    case 58: return "invalid ADLER32 encountered (checking ADLER32 can be disabled)";
    case 59: return "requested color conversion not supported";
    case 60: return "invalid window size given in the settings of the encoder (must be 0-32768)";
    case 61: return "invalid BTYPE given in the settings of the encoder (only 0, 1 and 2 are allowed)";
    /*LodePNG leaves the choice of RGB to grayscale conversion formula to the user.*/
    case 62: return "conversion from color to grayscale not supported";
    /*(2^31-1)*/
    case 63: return "length of a chunk too long, max allowed for PNG is 2147483647 bytes per chunk";
    /*this would result in the inability of a deflated block to ever contain an end code. It must be at least 1.*/
    case 64: return "the length of the END symbol 256 in the Huffman tree is 0";
    case 66: return "the length of a text chunk keyword given to the encoder is longer than the maximum of 79 bytes";
    case 67: return "the length of a text chunk keyword given to the encoder is smaller than the minimum of 1 byte";
    case 68: return "tried to encode a PLTE chunk with a palette that has less than 1 or more than 256 colors";
    case 69: return "unknown chunk type with 'critical' flag encountered by the decoder";
    case 71: return "invalid interlace mode given to encoder (must be 0 or 1)";
    case 72: return "while decoding, invalid compression method encountering in zTXt or iTXt chunk (it must be 0)";
    case 73: return "invalid tIME chunk size";
    case 74: return "invalid pHYs chunk size";
    /*length could be wrong, or data chopped off*/
    case 75: return "no null termination char found while decoding text chunk";
    case 76: return "iTXt chunk too short to contain required bytes";
    case 77: return "integer overflow in buffer size";
    case 78: return "failed to open file for reading"; /*file doesn't exist or couldn't be opened for reading*/
    case 79: return "failed to open file for writing";
    case 80: return "tried creating a tree of 0 symbols";
    case 81: return "lazy matching at pos 0 is impossible";
    case 82: return "color conversion to palette requested while a color isn't in palette, or index out of bounds";
    case 83: return "memory allocation failed";
    case 84: return "given image too small to contain all pixels to be encoded";
    case 86: return "impossible offset in lz77 encoding (internal bug)";
    case 87: return "must provide custom zlib function pointer if LODEPNG_COMPILE_ZLIB is not defined";
    case 88: return "invalid filter strategy given for LodePNGEncoderSettings.filter_strategy";
    case 89: return "text chunk keyword too short or long: must have size 1-79";
    /*the windowsize in the LodePNGCompressSettings. Requiring POT(==> & instead of %) makes encoding 12% faster.*/
    case 90: return "windowsize must be a power of two";
    case 91: return "invalid decompressed idat size";
    case 92: return "integer overflow due to too many pixels";
    case 93: return "zero width or height is invalid";
    case 94: return "header chunk must have a size of 13 bytes";
    case 95: return "integer overflow with combined idat chunk size";
    case 96: return "invalid gAMA chunk size";
    case 97: return "invalid cHRM chunk size";
    case 98: return "invalid sRGB chunk size";
    case 99: return "invalid sRGB rendering intent";
    case 100: return "invalid ICC profile color type, the PNG specification only allows RGB or GRAY";
    case 101: return "PNG specification does not allow RGB ICC profile on gray color types and vice versa";
    case 102: return "not allowed to set grayscale ICC profile with colored pixels by PNG specification";
    case 103: return "invalid palette index in bKGD chunk. Maybe it came before PLTE chunk?";
    case 104: return "invalid bKGD color while encoding (e.g. palette index out of range)";
    case 105: return "integer overflow of bitsize";
    case 106: return "PNG file must have PLTE chunk if color type is palette";
    case 107: return "color convert from palette mode requested without setting the palette data in it";
    case 108: return "tried to add more than 256 values to a palette";
  }
  return "unknown error code";
}
#endif /*LODEPNG_COMPILE_ERROR_TEXT*/