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115 lines
4.4 KiB
C
115 lines
4.4 KiB
C
/* deflate_fast.c -- compress data using the fast strategy of deflation algorithm
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*
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* Copyright (C) 1995-2013 Jean-loup Gailly and Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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*/
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#include "deflate.h"
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#include "deflate_p.h"
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#include "match.h"
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/* ===========================================================================
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* Compress as much as possible from the input stream, return the current
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* block state.
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* This function does not perform lazy evaluation of matches and inserts
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* new strings in the dictionary only for unmatched strings or for short
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* matches. It is used only for the fast compression options.
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*/
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block_state deflate_fast(deflate_state *s, int flush) {
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IPos hash_head; /* head of the hash chain */
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int bflush; /* set if current block must be flushed */
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for (;;) {
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/* Make sure that we always have enough lookahead, except
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* at the end of the input file. We need MAX_MATCH bytes
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* for the next match, plus MIN_MATCH bytes to insert the
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* string following the next match.
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*/
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if (s->lookahead < MIN_LOOKAHEAD) {
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fill_window(s);
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if (s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH) {
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return need_more;
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}
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if (s->lookahead == 0)
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break; /* flush the current block */
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}
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/* Insert the string window[strstart .. strstart+2] in the
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* dictionary, and set hash_head to the head of the hash chain:
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*/
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hash_head = NIL;
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if (s->lookahead >= MIN_MATCH) {
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hash_head = insert_string(s, s->strstart);
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}
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/* Find the longest match, discarding those <= prev_length.
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* At this point we have always match_length < MIN_MATCH
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*/
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if (hash_head != NIL && s->strstart - hash_head <= MAX_DIST(s)) {
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/* To simplify the code, we prevent matches with the string
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* of window index 0 (in particular we have to avoid a match
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* of the string with itself at the start of the input file).
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*/
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s->match_length = longest_match(s, hash_head);
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/* longest_match() sets match_start */
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}
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if (s->match_length >= MIN_MATCH) {
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check_match(s, s->strstart, s->match_start, s->match_length);
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_tr_tally_dist(s, s->strstart - s->match_start, s->match_length - MIN_MATCH, bflush);
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s->lookahead -= s->match_length;
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/* Insert new strings in the hash table only if the match length
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* is not too large. This saves time but degrades compression.
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*/
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if (s->match_length <= s->max_insert_length && s->lookahead >= MIN_MATCH) {
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s->match_length--; /* string at strstart already in table */
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s->strstart++;
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#ifdef NOT_TWEAK_COMPILER
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do {
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insert_string(s, s->strstart);
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s->strstart++;
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/* strstart never exceeds WSIZE-MAX_MATCH, so there are
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* always MIN_MATCH bytes ahead.
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*/
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} while (--s->match_length != 0);
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#else
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{
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bulk_insert_str(s, s->strstart, s->match_length);
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s->strstart += s->match_length;
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s->match_length = 0;
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}
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#endif
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} else {
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s->strstart += s->match_length;
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s->match_length = 0;
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s->ins_h = s->window[s->strstart];
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UPDATE_HASH(s, s->ins_h, s->strstart+2 - (MIN_MATCH));
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#if MIN_MATCH != 3
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Call UPDATE_HASH() MIN_MATCH-3 more times
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#endif
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/* If lookahead < MIN_MATCH, ins_h is garbage, but it does not
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* matter since it will be recomputed at next deflate call.
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*/
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}
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} else {
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/* No match, output a literal byte */
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Tracevv((stderr, "%c", s->window[s->strstart]));
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_tr_tally_lit(s, s->window[s->strstart], bflush);
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s->lookahead--;
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s->strstart++;
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}
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if (bflush)
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FLUSH_BLOCK(s, 0);
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}
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s->insert = s->strstart < MIN_MATCH-1 ? s->strstart : MIN_MATCH-1;
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if (flush == Z_FINISH) {
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FLUSH_BLOCK(s, 1);
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return finish_done;
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}
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if (s->last_lit)
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FLUSH_BLOCK(s, 0);
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return block_done;
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}
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