in zlib/deflate.c [1911:2031]
local block_state deflate_slow(deflate_state *s, int flush) {
IPos hash_head; /* head of hash chain */
int bflush; /* set if current block must be flushed */
/* Process the input block. */
for (;;) {
/* Make sure that we always have enough lookahead, except
* at the end of the input file. We need MAX_MATCH bytes
* for the next match, plus MIN_MATCH bytes to insert the
* string following the next match.
*/
if (s->lookahead < MIN_LOOKAHEAD) {
fill_window(s);
if (s->lookahead < MIN_LOOKAHEAD && flush == Z_NO_FLUSH) {
return need_more;
}
if (s->lookahead == 0) break; /* flush the current block */
}
/* Insert the string window[strstart .. strstart + 2] in the
* dictionary, and set hash_head to the head of the hash chain:
*/
hash_head = NIL;
if (s->lookahead >= MIN_MATCH) {
INSERT_STRING(s, s->strstart, hash_head);
}
/* Find the longest match, discarding those <= prev_length.
*/
s->prev_length = s->match_length, s->prev_match = s->match_start;
s->match_length = MIN_MATCH-1;
if (hash_head != NIL && s->prev_length < s->max_lazy_match &&
s->strstart - hash_head <= MAX_DIST(s)) {
/* To simplify the code, we prevent matches with the string
* of window index 0 (in particular we have to avoid a match
* of the string with itself at the start of the input file).
*/
s->match_length = longest_match (s, hash_head);
/* longest_match() sets match_start */
if (s->match_length <= 5 && (s->strategy == Z_FILTERED
#if TOO_FAR <= 32767
|| (s->match_length == MIN_MATCH &&
s->strstart - s->match_start > TOO_FAR)
#endif
)) {
/* If prev_match is also MIN_MATCH, match_start is garbage
* but we will ignore the current match anyway.
*/
s->match_length = MIN_MATCH-1;
}
}
/* If there was a match at the previous step and the current
* match is not better, output the previous match:
*/
if (s->prev_length >= MIN_MATCH && s->match_length <= s->prev_length) {
uInt max_insert = s->strstart + s->lookahead - MIN_MATCH;
/* Do not insert strings in hash table beyond this. */
check_match(s, s->strstart - 1, s->prev_match, s->prev_length);
_tr_tally_dist(s, s->strstart - 1 - s->prev_match,
s->prev_length - MIN_MATCH, bflush);
/* Insert in hash table all strings up to the end of the match.
* strstart - 1 and strstart are already inserted. If there is not
* enough lookahead, the last two strings are not inserted in
* the hash table.
*/
s->lookahead -= s->prev_length - 1;
s->prev_length -= 2;
do {
if (++s->strstart <= max_insert) {
INSERT_STRING(s, s->strstart, hash_head);
}
} while (--s->prev_length != 0);
s->match_available = 0;
s->match_length = MIN_MATCH-1;
s->strstart++;
if (bflush) FLUSH_BLOCK(s, 0);
} else if (s->match_available) {
/* If there was no match at the previous position, output a
* single literal. If there was a match but the current match
* is longer, truncate the previous match to a single literal.
*/
Tracevv((stderr,"%c", s->window[s->strstart - 1]));
_tr_tally_lit(s, s->window[s->strstart - 1], bflush);
if (bflush) {
FLUSH_BLOCK_ONLY(s, 0);
}
s->strstart++;
s->lookahead--;
if (s->strm->avail_out == 0) return need_more;
} else {
/* There is no previous match to compare with, wait for
* the next step to decide.
*/
s->match_available = 1;
s->strstart++;
s->lookahead--;
}
}
Assert (flush != Z_NO_FLUSH, "no flush?");
if (s->match_available) {
Tracevv((stderr,"%c", s->window[s->strstart - 1]));
_tr_tally_lit(s, s->window[s->strstart - 1], bflush);
s->match_available = 0;
}
s->insert = s->strstart < MIN_MATCH-1 ? s->strstart : MIN_MATCH-1;
if (flush == Z_FINISH) {
FLUSH_BLOCK(s, 1);
return finish_done;
}
if (s->sym_next)
FLUSH_BLOCK(s, 0);
return block_done;
}