| /* 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 "zutil_p.h" |
| #include "deflate.h" |
| #include "functable.h" |
| |
| #ifndef MATCH_TPL_H |
| #define MATCH_TPL_H |
| |
| #define EARLY_EXIT_TRIGGER_LEVEL 5 |
| |
| #endif |
| |
| /* Set match_start to the longest match starting at the given string and |
| * return its length. Matches shorter or equal to prev_length are discarded, |
| * in which case the result is equal to prev_length and match_start is garbage. |
| * |
| * IN assertions: cur_match is the head of the hash chain for the current |
| * string (strstart) and its distance is <= MAX_DIST, and prev_length >=1 |
| * OUT assertion: the match length is not greater than s->lookahead |
| */ |
| Z_INTERNAL uint32_t LONGEST_MATCH(deflate_state *const s, Pos cur_match) { |
| unsigned int strstart = s->strstart; |
| const unsigned wmask = s->w_mask; |
| unsigned char *window = s->window; |
| unsigned char *scan = window + strstart; |
| Z_REGISTER unsigned char *mbase_start = window; |
| Z_REGISTER unsigned char *mbase_end; |
| const Pos *prev = s->prev; |
| Pos limit; |
| #ifdef LONGEST_MATCH_SLOW |
| Pos limit_base; |
| #else |
| int32_t early_exit; |
| #endif |
| uint32_t chain_length, nice_match, best_len, offset; |
| uint32_t lookahead = s->lookahead; |
| Pos match_offset = 0; |
| #ifdef UNALIGNED_OK |
| uint8_t scan_start[8]; |
| #endif |
| uint8_t scan_end[8]; |
| |
| #define GOTO_NEXT_CHAIN \ |
| if (--chain_length && (cur_match = prev[cur_match & wmask]) > limit) \ |
| continue; \ |
| return best_len; |
| |
| /* 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 : STD_MIN_MATCH-1; |
| |
| /* Calculate read offset which should only extend an extra byte |
| * to find the next best match length. |
| */ |
| offset = best_len-1; |
| #ifdef UNALIGNED_OK |
| if (best_len >= sizeof(uint32_t)) { |
| offset -= 2; |
| #ifdef UNALIGNED64_OK |
| if (best_len >= sizeof(uint64_t)) |
| offset -= 4; |
| #endif |
| } |
| #endif |
| |
| #ifdef UNALIGNED64_OK |
| memcpy(scan_start, scan, sizeof(uint64_t)); |
| memcpy(scan_end, scan+offset, sizeof(uint64_t)); |
| #elif defined(UNALIGNED_OK) |
| memcpy(scan_start, scan, sizeof(uint32_t)); |
| memcpy(scan_end, scan+offset, sizeof(uint32_t)); |
| #else |
| scan_end[0] = *(scan+offset); |
| scan_end[1] = *(scan+offset+1); |
| #endif |
| mbase_end = (mbase_start+offset); |
| |
| /* Do not waste too much time if we already have a good match */ |
| chain_length = s->max_chain_length; |
| if (best_len >= s->good_match) |
| chain_length >>= 2; |
| nice_match = (uint32_t)s->nice_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; |
| #ifdef LONGEST_MATCH_SLOW |
| limit_base = limit; |
| if (best_len >= STD_MIN_MATCH) { |
| /* 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; |
| } |
| #else |
| early_exit = s->level < EARLY_EXIT_TRIGGER_LEVEL; |
| #endif |
| Assert((unsigned long)strstart <= s->window_size - MIN_LOOKAHEAD, "need lookahead"); |
| for (;;) { |
| if (cur_match >= strstart) |
| break; |
| |
| /* Skip to next match if the match length cannot increase or if the match length is |
| * less than 2. Note that the checks below for insufficient lookahead only occur |
| * occasionally for performance reasons. |
| * Therefore uninitialized memory will be accessed and conditional jumps will be made |
| * that depend on those values. However the length of the match is limited to the |
| * lookahead, so the output of deflate is not affected by the uninitialized values. |
| */ |
| #ifdef UNALIGNED_OK |
| if (best_len < sizeof(uint32_t)) { |
| for (;;) { |
| if (zng_memcmp_2(mbase_end+cur_match, scan_end) == 0 && |
| zng_memcmp_2(mbase_start+cur_match, scan_start) == 0) |
| break; |
| GOTO_NEXT_CHAIN; |
| } |
| # ifdef UNALIGNED64_OK |
| } else if (best_len >= sizeof(uint64_t)) { |
| for (;;) { |
| if (zng_memcmp_8(mbase_end+cur_match, scan_end) == 0 && |
| zng_memcmp_8(mbase_start+cur_match, scan_start) == 0) |
| break; |
| GOTO_NEXT_CHAIN; |
| } |
| # endif |
| } else { |
| for (;;) { |
| if (zng_memcmp_4(mbase_end+cur_match, scan_end) == 0 && |
| zng_memcmp_4(mbase_start+cur_match, scan_start) == 0) |
| break; |
| GOTO_NEXT_CHAIN; |
| } |
| } |
| #else |
| for (;;) { |
| if (mbase_end[cur_match] == scan_end[0] && mbase_end[cur_match+1] == scan_end[1] && |
| mbase_start[cur_match] == scan[0] && mbase_start[cur_match+1] == scan[1]) |
| break; |
| GOTO_NEXT_CHAIN; |
| } |
| #endif |
| uint32_t len = COMPARE256(scan+2, mbase_start+cur_match+2) + 2; |
| Assert(scan+len <= window+(unsigned)(s->window_size-1), "wild scan"); |
| |
| if (len > best_len) { |
| 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; |
| best_len = len; |
| if (best_len >= nice_match) |
| return best_len; |
| |
| offset = best_len-1; |
| #ifdef UNALIGNED_OK |
| if (best_len >= sizeof(uint32_t)) { |
| offset -= 2; |
| #ifdef UNALIGNED64_OK |
| if (best_len >= sizeof(uint64_t)) |
| offset -= 4; |
| #endif |
| } |
| #endif |
| |
| #ifdef UNALIGNED64_OK |
| memcpy(scan_end, scan+offset, sizeof(uint64_t)); |
| #elif defined(UNALIGNED_OK) |
| memcpy(scan_end, scan+offset, sizeof(uint32_t)); |
| #else |
| scan_end[0] = *(scan+offset); |
| scan_end[1] = *(scan+offset+1); |
| #endif |
| |
| #ifdef LONGEST_MATCH_SLOW |
| /* Look for a better string offset */ |
| if (UNLIKELY(len > STD_MIN_MATCH && match_start + len < strstart)) { |
| 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; |
| } |
| #endif |
| mbase_end = (mbase_start+offset); |
| } |
| #ifndef LONGEST_MATCH_SLOW |
| 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 |
| */ |
| break; |
| } |
| #endif |
| GOTO_NEXT_CHAIN; |
| } |
| return best_len; |
| |
| #ifdef LONGEST_MATCH_SLOW |
| break_matching: |
| |
| if (best_len < s->lookahead) |
| return best_len; |
| |
| return s->lookahead; |
| #endif |
| } |
| |
| #undef LONGEST_MATCH_SLOW |
| #undef LONGEST_MATCH |
| #undef COMPARE256 |
