table.m

#import <stdint.h>
#import "openssl/md5.h"
#import "openssl/evp.h"
#include "table.h"


static int random_compare(const void *_x, const void *_y) {
    uint32_t i = _i;
    uint64_t a = _a;
    uint8_t x = *((uint8_t *) _x);
    uint8_t y = *((uint8_t*) _y);
    return (a % (x + i) - a % (y + i));
}


static void merge(uint8_t *left, int llength, uint8_t *right, int rlength)
{
	/* Temporary memory locations for the 2 segments of the array to merge. */
	uint8_t *ltmp = (uint8_t *) malloc(llength * sizeof(uint8_t));
	uint8_t *rtmp = (uint8_t *) malloc(rlength * sizeof(uint8_t));
    
	/*
	 * Pointers to the elements being sorted in the temporary memory locations.
	 */
	uint8_t *ll = ltmp;
	uint8_t *rr = rtmp;
    
	uint8_t *result = left;
    
	/*
	 * Copy the segment of the array to be merged into the temporary memory
	 * locations.
	 */
	memcpy(ltmp, left, llength * sizeof(uint8_t));
	memcpy(rtmp, right, rlength * sizeof(uint8_t));
    
	while (llength > 0 && rlength > 0) {
		if (random_compare(ll, rr) <= 0) {
			/*
			 * Merge the first element from the left back into the main array
			 * if it is smaller or equal to the one on the right.
			 */
			*result = *ll;
			++ll;
			--llength;
		} else {
			/*
			 * Merge the first element from the right back into the main array
			 * if it is smaller than the one on the left.
			 */
			*result = *rr;
			++rr;
			--rlength;
		}
		++result;
	}
	/*
	 * All the elements from either the left or the right temporary array
	 * segment have been merged back into the main array.  Append the remaining
	 * elements from the other temporary array back into the main array.
	 */
	if (llength > 0)
		while (llength > 0) {
			/* Appending the rest of the left temporary array. */
			*result = *ll;
			++result;
			++ll;
			--llength;
		}
	else
		while (rlength > 0) {
			/* Appending the rest of the right temporary array. */
			*result = *rr;
			++result;
			++rr;
			--rlength;
		}
    
	/* Release the memory used for the temporary arrays. */
	free(ltmp);
	free(rtmp);
}

static void merge_sort(uint8_t array[], uint32_t length)
{
	/* This is the middle index and also the length of the right array. */
	uint8_t middle;
    
	/*
	 * Pointers to the beginning of the left and right segment of the array
	 * to be merged.
	 */
	uint8_t *left, *right;
    
	/* Length of the left segment of the array to be merged. */
	uint32_t llength;
    
	if (length <= 1)
		return;
    
	/* Let integer division truncate the value. */
	middle = (uint8_t)(length / 2);
    
	llength = length - middle;
    
	/*
	 * Set the pointers to the appropriate segments of the array to be merged.
	 */
	left = array;
	right = array + llength;
    
	merge_sort(left, llength);
	merge_sort(right, middle);
	merge(left, llength, right, middle);
}

void table_encrypt(unsigned char *buf, size_t len) {
    unsigned char *end = buf + len;
    while (buf < end) {
        *buf = encrypt_table[*buf];
        buf++;
    }
}

void table_decrypt(unsigned char *buf, size_t len) {
    unsigned char *end = buf + len;
    while (buf < end) {
        *buf = decrypt_table[*buf];
        buf++;
    }
}

void get_table(const unsigned char* key) {
    unsigned char *table = encrypt_table;
    unsigned char tmp_hash[16];
    //    tmp_hash = MD5((const unsigned char*)key, strlen(key), NULL);
    MD5(key, strlen((const char *)key), tmp_hash);
    _a = *(unsigned long long *)tmp_hash;
    _a = *(uint64_t *)tmp_hash;
    uint32_t i;
    
    for(i = 0; i < 256; ++i) {
        table[i] = (unsigned char)i;
    }
    for(i = 1; i < 1024; ++i) {
        _i = i;
        merge_sort(table, 256);
    }
    for(i = 0; i < 256; ++i) {
        // gen decrypt table from encrypt table
        decrypt_table[encrypt_table[i]] = (unsigned char)i;
    }
}