117 lines
3.2 KiB
C
117 lines
3.2 KiB
C
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/*
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* genlz77 - Generic LZ77 compressor
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*
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* Copyright (c) 2014 by Paul Sokolovsky
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*
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* This software is provided 'as-is', without any express
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* or implied warranty. In no event will the authors be
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* held liable for any damages arising from the use of
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* this software.
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*
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* Permission is granted to anyone to use this software
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* for any purpose, including commercial applications,
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* and to alter it and redistribute it freely, subject to
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* the following restrictions:
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*
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* 1. The origin of this software must not be
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* misrepresented; you must not claim that you
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* wrote the original software. If you use this
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* software in a product, an acknowledgment in
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* the product documentation would be appreciated
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* but is not required.
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*
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* 2. Altered source versions must be plainly marked
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* as such, and must not be misrepresented as
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* being the original software.
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*
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* 3. This notice may not be removed or altered from
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* any source distribution.
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*/
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#include <stdint.h>
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#include <string.h>
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#include <stdio.h>
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#include "defl_static.h"
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#define HASH_BITS 10
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#define HASH_SIZE (1<<HASH_BITS)
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/* Minimum and maximum length of matches to look for, inclusive */
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#define MIN_MATCH 3
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#define MAX_MATCH 258
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/* Max offset of the match to look for, inclusive */
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#define MAX_OFFSET 32768
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/* Hash function can be defined as macro or as inline function */
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/*#define HASH(p) (p[0] + p[1] + p[2])*/
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/* This is hash function from liblzf */
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static int HASH(const uint8_t *p) {
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int v = (p[0] << 16) | (p[1] << 8) | p[2];
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int hash = ((v >> (3*8 - HASH_BITS)) - v) & (HASH_SIZE - 1);
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return hash;
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}
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#ifdef DUMP_LZTXT
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/* Counter for approximate compressed length in LZTXT mode. */
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/* Literal is counted as 1, copy as 2 bytes. */
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unsigned approx_compressed_len;
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void literal(void *data, uint8_t val)
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{
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printf("L%02x # %c\n", val, (val >= 0x20 && val <= 0x7e) ? val : '?');
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approx_compressed_len++;
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}
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void copy(void *data, unsigned offset, unsigned len)
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{
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printf("C-%u,%u\n", offset, len);
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approx_compressed_len += 2;
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}
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#else
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static void literal(void *data, uint8_t val)
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{
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zlib_literal(data, val);
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}
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static void copy(void *data, unsigned offset, unsigned len)
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{
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zlib_match(data, offset, len);
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}
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#endif
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void tinf_compress(void *data, const uint8_t *src, unsigned slen)
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{
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const uint8_t *hashtable[HASH_SIZE] = {0};
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const uint8_t *top = src + slen - MIN_MATCH;
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while (src < top) {
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int h = HASH(src);
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const uint8_t **bucket = &hashtable[h & (HASH_SIZE - 1)];
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const uint8_t *subs = *bucket;
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*bucket = src;
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if (subs && src > subs && (src - subs) <= MAX_OFFSET && !memcmp(src, subs, MIN_MATCH)) {
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src += MIN_MATCH;
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const uint8_t *m = subs + MIN_MATCH;
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int len = MIN_MATCH;
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while (*src == *m && len < MAX_MATCH) {
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src++; m++; len++;
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}
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copy(data, src - len - subs, len);
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} else {
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literal(data, *src++);
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}
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}
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// Process buffer tail, which is less than MIN_MATCH
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// (and so it doesn't make sense to look for matches there)
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top += MIN_MATCH;
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while (src < top) {
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literal(data, *src++);
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}
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}
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