From: Nathan Moinvaziri Date: Tue, 15 Jun 2021 00:40:03 +0000 (-0700) Subject: Incorporate fast-zlib algorithm changes into longest_match. X-Git-Tag: 2.1.0-beta1~549 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d87a9f96d0dd863e9cd330a8400e66e93760997d;p=thirdparty%2Fzlib-ng.git Incorporate fast-zlib algorithm changes into longest_match. --- diff --git a/match_tpl.h b/match_tpl.h index 04eac1aa8..3d8ac4e3c 100644 --- a/match_tpl.h +++ b/match_tpl.h @@ -1,3 +1,12 @@ +/* match_tpl.h -- find longest match template for compare256 variants + * + * Copyright (C) 1995-2013 Jean-loup Gailly and Mark Adler + * For conditions of distribution and use, see copyright notice in zlib.h + * + * Portions copyright (C) 2014-2021 Konstantin Nosov + * Fast-zlib optimized longest_match + * https://github.com/gildor2/fast_zlib + */ #include "zbuild.h" #include "deflate.h" @@ -36,10 +45,12 @@ Z_INTERNAL uint32_t LONGEST_MATCH(deflate_state *const s, Pos cur_match) { Z_REGISTER unsigned char *mbase_start = window; Z_REGISTER unsigned char *mbase_end; const Pos *prev = s->prev; - Pos limit; + Pos limit, limit_base; int32_t early_exit; uint32_t chain_length, nice_match, best_len, offset; uint32_t lookahead = s->lookahead; + Pos match_offset = 0; + int32_t rolling_hash; bestcmp_t scan_end; #ifndef UNALIGNED_OK bestcmp_t scan_end0; @@ -55,7 +66,7 @@ Z_INTERNAL uint32_t LONGEST_MATCH(deflate_state *const s, Pos cur_match) { /* The code is optimized for STD_MAX_MATCH-2 multiple of 16. */ Assert(STD_MAX_MATCH == 258, "Code too clever"); - best_len = s->prev_length ? s->prev_length : 1; + best_len = s->prev_length ? s->prev_length : STD_MIN_MATCH-1; /* Calculate read offset which should only extend an extra byte * to find the next best match length. @@ -81,6 +92,7 @@ Z_INTERNAL uint32_t LONGEST_MATCH(deflate_state *const s, Pos cur_match) { /* Do not waste too much time if we already have a good match */ chain_length = s->max_chain_length; + rolling_hash = chain_length > 1024; early_exit = s->level < EARLY_EXIT_TRIGGER_LEVEL; if (best_len >= s->good_match) chain_length >>= 2; @@ -89,7 +101,38 @@ Z_INTERNAL uint32_t LONGEST_MATCH(deflate_state *const s, Pos cur_match) { /* Stop when cur_match becomes <= limit. To simplify the code, * we prevent matches with the string of window index 0 */ - limit = strstart > MAX_DIST(s) ? (Pos)(strstart - MAX_DIST(s)) : 0; + limit = limit_base = strstart > MAX_DIST(s) ? (Pos)(strstart - MAX_DIST(s)) : 0; + + if (best_len >= STD_MIN_MATCH && rolling_hash) { + /* We're continuing search (lazy evaluation). */ + uint32_t i, hash; + Pos pos; + + /* Find a most distant chain starting from scan with index=1 (index=0 corresponds + * to cur_match). We cannot use s->prev[strstart+1,...] immediately, because + * these strings are not yet inserted into the hash table. + */ + hash = s->update_hash(s, 0, scan[1]); + hash = s->update_hash(s, hash, scan[2]); + + for (i = 3; i <= best_len; i++) { + hash = s->update_hash(s, hash, scan[i]); + + /* If we're starting with best_len >= 3, we can use offset search. */ + pos = s->head[hash]; + if (pos < cur_match) { + match_offset = (Pos)(i - 2); + cur_match = pos; + } + } + + /* Update offset-dependent variables */ + limit = limit_base+match_offset; + if (cur_match <= limit) + goto break_matching; + mbase_start -= match_offset; + mbase_end -= match_offset; + } Assert((unsigned long)strstart <= s->window_size - MIN_LOOKAHEAD, "need lookahead"); for (;;) { @@ -140,7 +183,9 @@ Z_INTERNAL uint32_t LONGEST_MATCH(deflate_state *const s, Pos cur_match) { Assert(scan+len <= window+(unsigned)(s->window_size-1), "wild scan"); if (len > best_len) { - s->match_start = cur_match; + uint32_t match_start = cur_match - match_offset; + s->match_start = match_start; + /* Do not look for matches beyond the end of the input. */ if (len > lookahead) return lookahead; @@ -162,7 +207,56 @@ Z_INTERNAL uint32_t LONGEST_MATCH(deflate_state *const s, Pos cur_match) { #ifndef UNALIGNED_OK scan_end0 = *(bestcmp_t *)(scan+offset+1); #endif - mbase_end = (mbase_start+offset); + /* Look for a better string offset */ + if (len > STD_MIN_MATCH && match_start + len < strstart && rolling_hash) { + Pos pos, next_pos; + uint32_t i, hash; + unsigned char *scan_endstr; + + /* Go back to offset 0 */ + cur_match -= match_offset; + match_offset = 0; + next_pos = cur_match; + for (i = 0; i <= len - STD_MIN_MATCH; i++) { + pos = prev[(cur_match + i) & wmask]; + if (pos < next_pos) { + /* Hash chain is more distant, use it */ + if (pos <= limit_base + i) + goto break_matching; + next_pos = pos; + match_offset = (Pos)i; + } + } + /* Switch cur_match to next_pos chain */ + cur_match = next_pos; + + /* Try hash head at len-(STD_MIN_MATCH-1) position to see if we could get + * a better cur_match at the end of string. Using (STD_MIN_MATCH-1) lets + * us include one more byte into hash - the byte which will be checked + * in main loop now, and which allows to grow match by 1. + */ + scan_endstr = scan + len - (STD_MIN_MATCH+1); + + hash = s->update_hash(s, 0, scan_endstr[0]); + hash = s->update_hash(s, hash, scan_endstr[1]); + hash = s->update_hash(s, hash, scan_endstr[2]); + + pos = s->head[hash]; + if (pos < cur_match) { + match_offset = (Pos)(len - (STD_MIN_MATCH+1)); + if (pos <= limit_base + match_offset) + goto break_matching; + cur_match = pos; + } + + /* Update offset-dependent variables */ + limit = limit_base+match_offset; + mbase_start = window-match_offset; + mbase_end = (mbase_start+offset); + continue; + } else { + mbase_end = (mbase_start+offset); + } } else if (UNLIKELY(early_exit)) { /* The probability of finding a match later if we here is pretty low, so for * performance it's best to outright stop here for the lower compression levels @@ -171,8 +265,14 @@ Z_INTERNAL uint32_t LONGEST_MATCH(deflate_state *const s, Pos cur_match) { } GOTO_NEXT_CHAIN; } - return best_len; + +break_matching: + + if (best_len < s->lookahead) + return best_len; + + return s->lookahead; } #undef LONGEST_MATCH