bzip2.js

/* 
  bzip2.js - a small bzip2 decompression implementation
  
  Copyright 2011 by antimatter15 (antimatter15@gmail.com)
  
  Based on micro-bunzip by Rob Landley (rob@landley.net).

  Copyright (c) 2011 by antimatter15 (antimatter15@gmail.com).

  Permission is hereby granted, free of charge, to any person obtaining a
  copy of this software and associated documentation files (the "Software"),
  to deal in the Software without restriction, including without limitation
  the rights to use, copy, modify, merge, publish, distribute, sublicense,
  and/or sell copies of the Software, and to permit persons to whom the
  Software is furnished to do so, subject to the following conditions:
  
  The above copyright notice and this permission notice shall be included
  in all copies or substantial portions of the Software.
  
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
  DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH
  THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

var bzip2 = {};

bzip2.array = function(bytes){
  var bit = 0, byte = 0;
  var BITMASK = [0, 0x01, 0x03, 0x07, 0x0F, 0x1F, 0x3F, 0x7F, 0xFF ];
  return function(n){
    var result = 0;
    while(n > 0){
      var left = 8 - bit;
      if(n >= left){
        result <<= left;
        result |= (BITMASK[left] & bytes[byte++]);
        bit = 0;
        n -= left;
      }else{
        result <<= n;
        result |= ((bytes[byte] & (BITMASK[n] << (8 - n - bit))) >> (8 - n - bit));
        bit += n;
        n = 0;
      }
    }
    return result
  }
}

bzip2.simple = function(bits){
  var size = bzip2.header(bits);
  var all = '', chunk = '';
  do{
    all += chunk;
    chunk = bzip2.decompress(bits, size);
  }while(chunk != -1);
  return all;
}

bzip2.header = function(bits){
  if(bits(8*3) != 4348520) throw "No magic number found";
  var i = bits(8) - 48;
  if(i < 1 || i > 9) throw "Not a BZIP archive";
  return i;
};


//takes a function for reading the block data (starting with 0x314159265359)
//a block size (0-9) (optional, defaults to 9)
//a length at which to stop decompressing and return the output
bzip2.decompress = function(bits, size, len){
  var MAX_HUFCODE_BITS = 20;
  var MAX_SYMBOLS = 258;
  var SYMBOL_RUNA = 0;
  var SYMBOL_RUNB = 1;
  var GROUP_SIZE = 50;
  
  var bufsize = 100000 * size;
  for(var h = '', i = 0; i < 6; i++) h += bits(8).toString(16);
  if(h == "177245385090") return -1; //last block
  if(h != "314159265359") throw "eek not valid bzip data";
  bits(32); //ignore CRC codes
  if(bits(1)) throw "unsupported obsolete version";
  var origPtr = bits(24);
  if(origPtr > bufsize) throw "Initial position larger than buffer size";
  var t = bits(16);
  var symToByte = new Uint8Array(256), 
      symTotal = 0;
  for (i = 0; i < 16; i++) {
    if(t & (1 << (15 - i))) {
      var k = bits(16);
      for(j = 0; j < 16; j++){
        if(k & (1 << (15 - j))){
          symToByte[symTotal++] = (16 * i) + j;
        }
      }
    }
  }

  var groupCount = bits(3);
  if(groupCount < 2 || groupCount > 6) throw "another error";
  var nSelectors = bits(15);
  if(nSelectors == 0) throw "meh";
  var mtfSymbol = []; //TODO: possibly replace JS array with typed arrays
  for(var i = 0; i < groupCount; i++) mtfSymbol[i] = i;
  var selectors = new Uint8Array(32768);
  
  for(var i = 0; i < nSelectors; i++){
    for(var j = 0; bits(1); j++) if(j >= groupCount) throw "whoops another error"; 
    var uc = mtfSymbol[j];
    mtfSymbol.splice(j, 1); //this is a probably inefficient MTF transform
    mtfSymbol.splice(0, 0, uc);
    selectors[i] = uc;
  }
  
  var symCount = symTotal + 2;
  var groups = [];
  for(var j = 0; j < groupCount; j++){
    var length = new Uint8Array(MAX_SYMBOLS), 
        temp = new Uint8Array(MAX_HUFCODE_BITS+1);
    t = bits(5); //lengths
    for(var i = 0; i < symCount; i++){
      while(true){
        if (t < 1 || t > MAX_HUFCODE_BITS) throw "I gave up a while ago on writing error messages";
        if(!bits(1)) break;
        if(!bits(1)) t++;
        else t--;
      }
      length[i] = t;
    }
    var  minLen,  maxLen;
    minLen = maxLen = length[0];
    for(var i = 1; i < symCount; i++){
      if(length[i] > maxLen) maxLen = length[i];
      else if(length[i] < minLen) minLen = length[i];
    }
    var hufGroup;
    hufGroup = groups[j] = {};
    hufGroup.permute = new Uint32Array(MAX_SYMBOLS);
    hufGroup.limit = new Uint32Array(MAX_HUFCODE_BITS + 1);
    hufGroup.base = new Uint32Array(MAX_HUFCODE_BITS + 1);
    hufGroup.minLen = minLen;
    hufGroup.maxLen = maxLen;
    var base = hufGroup.base.subarray(1);
    var limit = hufGroup.limit.subarray(1);
    var pp = 0;
    for(var i = minLen; i <= maxLen; i++)
      for(var t = 0; t < symCount; t++) 
      if(length[t] == i) hufGroup.permute[pp++] = t;
      for(i = minLen; i <= maxLen; i++) temp[i] = limit[i] = 0;
      for(i = 0; i < symCount; i++) temp[length[i]]++;
      pp = t = 0;
      for(i = minLen; i < maxLen; i++) {
        pp += temp[i];
        limit[i] = pp - 1;
        pp <<= 1;
        base[i+1] = pp - (t += temp[i]);
      }
      limit[maxLen]=pp+temp[maxLen]-1;
      base[minLen]=0;
  }
  var byteCount = new Uint32Array(256);
  for(var i = 0; i < 256; i++) mtfSymbol[i] = i;
  var runPos, count, symCount, selector;
  runPos = count = symCount = selector = 0;
  var buf = new Uint32Array(bufsize);
  while(true){
    if(!(symCount--)){
      symCount = GROUP_SIZE - 1;
      if(selector >= nSelectors) throw "meow i'm a kitty, that's an error";
      hufGroup = groups[selectors[selector++]];
      base = hufGroup.base.subarray(1);
      limit = hufGroup.limit.subarray(1);
    }
    i = hufGroup.minLen;
    j = bits(i);
    while(true){
      if(i > hufGroup.maxLen) throw "rawr i'm a dinosaur";
      if(j <= limit[i]) break;
      i++;
      j = (j << 1) | bits(1);
    }
    j -= base[i];
    if(j < 0 || j >= MAX_SYMBOLS) throw "moo i'm a cow";
    var nextSym = hufGroup.permute[j];
    if (nextSym == SYMBOL_RUNA || nextSym == SYMBOL_RUNB) {
      if(!runPos){
        runPos = 1;
        t = 0;
      }
      if(nextSym == SYMBOL_RUNA) t += runPos;
      else t += 2 * runPos;
      runPos <<= 1;
      continue;
    }
    if(runPos){
      runPos = 0;
      if(count + t >= bufsize) throw "Boom.";
      uc = symToByte[mtfSymbol[0]];
      byteCount[uc] += t;
      while(t--) buf[count++] = uc;
    }
    if(nextSym > symTotal) break;
    if(count >= bufsize) throw "I can't think of anything. Error";
    i = nextSym -1;
    uc = mtfSymbol[i];
    mtfSymbol.splice(i, 1);
    mtfSymbol.splice(0, 0, uc);
    uc = symToByte[uc];
    byteCount[uc]++;
    buf[count++] = uc;
  }
  if(origPtr < 0 || origPtr >= count) throw "I'm a monkey and I'm throwing something at someone, namely you";
  var j = 0;
  for(var i = 0; i < 256; i++){
    k = j + byteCount[i];
    byteCount[i] = j;
    j = k;
  }
  for(var i = 0; i < count; i++){
    uc = buf[i] & 0xff;
    buf[byteCount[uc]] |= (i << 8);
    byteCount[uc]++;
  }
  var pos = 0, current = 0, run = 0;
  if(count) {
    pos = buf[origPtr];
    current = (pos & 0xff);
    pos >>= 8;
    run = -1;
  }
  count = count;
  var output = '';
  var copies, previous, outbyte;
  if(!len) len = Infinity;
  while(count){
    count--;
    previous = current;
    pos = buf[pos];
    current = pos & 0xff;
    pos >>= 8;
    if(run++ == 3){
      copies = current;
      outbyte = previous;
      current = -1;
    }else{
      copies = 1;
      outbyte = current;
    }
    while(copies--){
      output += (String.fromCharCode(outbyte));
      if(!--len) return output;
    }
    if(current != previous) run = 0;
  }
  return output;
}