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ClickHouse/contrib/libzlib-ng/match.c
Alexey Zatelepin 8f74b844fc import zlib-ng sources from 343c4c5491 [#METR-23582]
2017-01-08 21:26:03 +03:00

472 lines
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/*
* 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
*/
#include "deflate.h"
#if (defined(UNALIGNED_OK) && MAX_MATCH == 258)
/* Only use std3_longest_match for little_endian systems, also avoid using it with
non-gcc compilers since the __builtin_ctzl() function might not be optimized. */
# if defined(__GNUC__) && defined(HAVE_BUILTIN_CTZL) && ((__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__) \
|| defined(__LITTLE_ENDIAN__))
# define std3_longest_match
# elif(defined(_MSC_VER) && defined(_WIN32))
# define std3_longest_match
# else
# define std2_longest_match
# endif
#else
# define std1_longest_match
#endif
#if defined(_MSC_VER) && !defined(__clang__)
#include <intrin.h>
/* This is not a general purpose replacement for __builtin_ctzl. The function expects that value is != 0
* Because of that assumption trailing_zero is not initialized and the return value of _BitScanForward is not checked
*/
static __forceinline unsigned long __builtin_ctzl(unsigned long value)
{
unsigned long trailing_zero;
_BitScanForward(&trailing_zero, value);
return trailing_zero;
}
#endif
#ifdef std1_longest_match
/*
* Standard longest_match
*
*/
ZLIB_INTERNAL unsigned longest_match(deflate_state *const s, IPos cur_match) {
const unsigned wmask = s->w_mask;
const Pos *prev = s->prev;
unsigned chain_length;
IPos limit;
unsigned int len, best_len, nice_match;
unsigned char *scan, *match, *strend, scan_end, scan_end1;
/*
* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple
* of 16. It is easy to get rid of this optimization if necessary.
*/
Assert(s->hash_bits >= 8 && MAX_MATCH == 258, "Code too clever");
/*
* Do not waste too much time if we already have a good match
*/
best_len = s->prev_length;
chain_length = s->max_chain_length;
if (best_len >= s->good_match)
chain_length >>= 2;
/*
* Do not looks for matches beyond the end of the input. This is
* necessary to make deflate deterministic
*/
nice_match = (unsigned int)s->nice_match > s->lookahead ? s->lookahead : s->nice_match;
/*
* Stop when cur_match becomes <= limit. To simplify the code,
* we prevent matches with the string of window index 0
*/
limit = s->strstart > MAX_DIST(s) ? s->strstart - MAX_DIST(s) : 0;
scan = s->window + s->strstart;
strend = s->window + s->strstart + MAX_MATCH;
scan_end1 = scan[best_len-1];
scan_end = scan[best_len];
Assert((unsigned long)s->strstart <= s->window_size - MIN_LOOKAHEAD, "need lookahead");
do {
Assert(cur_match < s->strstart, "no future");
match = s->window + cur_match;
/*
* 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.
*/
if (match[best_len] != scan_end ||
match[best_len-1] != scan_end1 ||
*match != *scan ||
*++match != scan[1])
continue;
/*
* The check at best_len-1 can be removed because it will
* be made again later. (This heuristic is not always a win.)
* It is not necessary to compare scan[2] and match[2] since
* they are always equal when the other bytes match, given
* that the hash keys are equal and that HASH_BITS >= 8.
*/
scan += 2;
match++;
Assert(*scan == *match, "match[2]?");
/*
* We check for insufficient lookahead only every 8th
* comparision; the 256th check will be made at strstart + 258.
*/
do {
} while (*++scan == *++match && *++scan == *++match &&
*++scan == *++match && *++scan == *++match &&
*++scan == *++match && *++scan == *++match &&
*++scan == *++match && *++scan == *++match &&
scan < strend);
Assert(scan <= s->window+(unsigned int)(s->window_size-1), "wild scan");
len = MAX_MATCH - (int)(strend - scan);
scan = strend - MAX_MATCH;
if (len > best_len) {
s->match_start = cur_match;
best_len = len;
if (len >= nice_match)
break;
scan_end1 = scan[best_len-1];
scan_end = scan[best_len];
} else {
/*
* 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
*/
if (s->level < 6)
break;
}
} while ((cur_match = prev[cur_match & wmask]) > limit && --chain_length);
if ((unsigned int)best_len <= s->lookahead)
return best_len;
return s->lookahead;
}
#endif
#ifdef std2_longest_match
/*
* UNALIGNED_OK longest_match
*
*/
ZLIB_INTERNAL unsigned longest_match(deflate_state *const s, IPos cur_match) {
const unsigned wmask = s->w_mask;
const Pos *prev = s->prev;
uint16_t scan_start, scan_end;
unsigned chain_length;
IPos limit;
unsigned int len, best_len, nice_match;
unsigned char *scan, *strend;
/*
* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple
* of 16. It is easy to get rid of this optimization if necessary.
*/
Assert(s->hash_bits >= 8 && MAX_MATCH == 258, "Code too clever");
/*
* Do not waste too much time if we already have a good match
*/
best_len = s->prev_length;
chain_length = s->max_chain_length;
if (best_len >= s->good_match)
chain_length >>= 2;
/*
* Do not looks for matches beyond the end of the input. This is
* necessary to make deflate deterministic
*/
nice_match = (unsigned int)s->nice_match > s->lookahead ? s->lookahead : s->nice_match;
/*
* Stop when cur_match becomes <= limit. To simplify the code,
* we prevent matches with the string of window index 0
*/
limit = s->strstart > MAX_DIST(s) ? s->strstart - MAX_DIST(s) : 0;
scan = s->window + s->strstart;
strend = s->window + s->strstart + MAX_MATCH - 1;
scan_start = *(uint16_t *)scan;
scan_end = *(uint16_t *)(scan + best_len-1);
Assert((unsigned long)s->strstart <= s->window_size - MIN_LOOKAHEAD, "need lookahead");
do {
unsigned char *match;
Assert(cur_match < s->strstart, "no future");
match = s->window + cur_match;
/*
* 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.
*/
if (likely((*(uint16_t *)(match + best_len - 1) != scan_end)))
continue;
if (*(uint16_t *)match != scan_start)
continue;
/* It is not necessary to compare scan[2] and match[2] since
* they are always equal when the other bytes match, given that
* the hash keys are equal and that HASH_BITS >= 8. Compare 2
* bytes at a time at strstart+3, +5, ... up to strstart+257.
* We check for insufficient lookahead only every 4th
* comparison; the 128th check will be made at strstart+257.
* If MAX_MATCH-2 is not a multiple of 8, it is necessary to
* put more guard bytes at the end of the window, or to check
* more often for insufficient lookahead.
*/
Assert(scan[2] == match[2], "scan[2]?");
scan++;
match++;
do {
} while (*(uint16_t *)(scan += 2)== *(uint16_t *)(match += 2) &&
*(uint16_t *)(scan += 2)== *(uint16_t *)(match += 2) &&
*(uint16_t *)(scan += 2)== *(uint16_t *)(match += 2) &&
*(uint16_t *)(scan += 2)== *(uint16_t *)(match += 2) &&
scan < strend);
/*
* Here, scan <= window + strstart + 257
*/
Assert(scan <= s->window+(unsigned)(s->window_size-1), "wild scan");
if (*scan == *match)
scan++;
len = (MAX_MATCH -1) - (int)(strend-scan);
scan = strend - (MAX_MATCH-1);
if (len > best_len) {
s->match_start = cur_match;
best_len = len;
if (len >= nice_match)
break;
scan_end = *(uint16_t *)(scan + best_len - 1);
} else {
/*
* 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
*/
if (s->level < 6)
break;
}
} while (--chain_length && (cur_match = prev[cur_match & wmask]) > limit);
if ((unsigned)best_len <= s->lookahead)
return best_len;
return s->lookahead;
}
#endif
#ifdef std3_longest_match
/* longest_match() with minor change to improve performance (in terms of
* execution time).
*
* The pristine longest_match() function is sketched bellow (strip the
* then-clause of the "#ifdef UNALIGNED_OK"-directive)
*
* ------------------------------------------------------------
* unsigned int longest_match(...) {
* ...
* do {
* match = s->window + cur_match; //s0
* if (*(ushf*)(match+best_len-1) != scan_end || //s1
* *(ushf*)match != scan_start) continue; //s2
* ...
*
* do {
* } while (*(ushf*)(scan+=2) == *(ushf*)(match+=2) &&
* *(ushf*)(scan+=2) == *(ushf*)(match+=2) &&
* *(ushf*)(scan+=2) == *(ushf*)(match+=2) &&
* *(ushf*)(scan+=2) == *(ushf*)(match+=2) &&
* scan < strend); //s3
*
* ...
* } while(cond); //s4
*
* -------------------------------------------------------------
*
* The change include:
*
* 1) The hottest statements of the function is: s0, s1 and s4. Pull them
* together to form a new loop. The benefit is two-fold:
*
* o. Ease the compiler to yield good code layout: the conditional-branch
* corresponding to s1 and its biased target s4 become very close (likely,
* fit in the same cache-line), hence improving instruction-fetching
* efficiency.
*
* o. Ease the compiler to promote "s->window" into register. "s->window"
* is loop-invariant; it is supposed to be promoted into register and keep
* the value throughout the entire loop. However, there are many such
* loop-invariant, and x86-family has small register file; "s->window" is
* likely to be chosen as register-allocation victim such that its value
* is reloaded from memory in every single iteration. By forming a new loop,
* "s->window" is loop-invariant of that newly created tight loop. It is
* lot easier for compiler to promote this quantity to register and keep
* its value throughout the entire small loop.
*
* 2) Transfrom s3 such that it examines sizeof(long)-byte-match at a time.
* This is done by:
* ------------------------------------------------
* v1 = load from "scan" by sizeof(long) bytes
* v2 = load from "match" by sizeof(lnog) bytes
* v3 = v1 xor v2
* match-bit = little-endian-machine(yes-for-x86) ?
* count-trailing-zero(v3) :
* count-leading-zero(v3);
*
* match-byte = match-bit/8
*
* "scan" and "match" advance if necessary
* -------------------------------------------------
*/
ZLIB_INTERNAL unsigned longest_match(deflate_state *const s, IPos cur_match) {
unsigned chain_length = s->max_chain_length;/* max hash chain length */
register unsigned char *scan = s->window + s->strstart; /* current string */
register unsigned char *match; /* matched string */
register unsigned int len; /* length of current match */
unsigned int best_len = s->prev_length; /* best match length so far */
unsigned int nice_match = s->nice_match; /* stop if match long enough */
IPos limit = s->strstart > (IPos)MAX_DIST(s) ?
s->strstart - (IPos)MAX_DIST(s) : NIL;
/* Stop when cur_match becomes <= limit. To simplify the code,
* we prevent matches with the string of window index 0.
*/
Pos *prev = s->prev;
unsigned int wmask = s->w_mask;
register unsigned char *strend = s->window + s->strstart + MAX_MATCH;
register uint16_t scan_start = *(uint16_t*)scan;
register uint16_t scan_end = *(uint16_t*)(scan+best_len-1);
/* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16.
* It is easy to get rid of this optimization if necessary.
*/
Assert(s->hash_bits >= 8 && MAX_MATCH == 258, "Code too clever");
/* Do not waste too much time if we already have a good match: */
if (s->prev_length >= s->good_match) {
chain_length >>= 2;
}
/* Do not look for matches beyond the end of the input. This is necessary
* to make deflate deterministic.
*/
if ((unsigned int)nice_match > s->lookahead) nice_match = s->lookahead;
Assert((unsigned long)s->strstart <= s->window_size-MIN_LOOKAHEAD, "need lookahead");
do {
Assert(cur_match < s->strstart, "no future");
/* 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.
*/
unsigned char *win = s->window;
int cont = 1;
do {
match = win + cur_match;
if (likely(*(uint16_t*)(match+best_len-1) != scan_end)) {
if ((cur_match = prev[cur_match & wmask]) > limit
&& --chain_length != 0) {
continue;
} else {
cont = 0;
}
}
break;
} while (1);
if (!cont)
break;
if (*(uint16_t*)match != scan_start)
continue;
/* It is not necessary to compare scan[2] and match[2] since they are
* always equal when the other bytes match, given that the hash keys
* are equal and that HASH_BITS >= 8. Compare 2 bytes at a time at
* strstart+3, +5, ... up to strstart+257. We check for insufficient
* lookahead only every 4th comparison; the 128th check will be made
* at strstart+257. If MAX_MATCH-2 is not a multiple of 8, it is
* necessary to put more guard bytes at the end of the window, or
* to check more often for insufficient lookahead.
*/
scan += 2, match+=2;
Assert(*scan == *match, "match[2]?");
do {
unsigned long sv = *(unsigned long*)(void*)scan;
unsigned long mv = *(unsigned long*)(void*)match;
unsigned long xor = sv ^ mv;
if (xor) {
int match_byte = __builtin_ctzl(xor) / 8;
scan += match_byte;
match += match_byte;
break;
} else {
scan += sizeof(unsigned long);
match += sizeof(unsigned long);
}
} while (scan < strend);
if (scan > strend)
scan = strend;
Assert(scan <= s->window+(unsigned)(s->window_size-1), "wild scan");
len = MAX_MATCH - (int)(strend - scan);
scan = strend - MAX_MATCH;
if (len > best_len) {
s->match_start = cur_match;
best_len = len;
if (len >= nice_match)
break;
scan_end = *(uint16_t*)(scan+best_len-1);
} else {
/*
* 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
*/
if (s->level < 6)
break;
}
} while ((cur_match = prev[cur_match & wmask]) > limit && --chain_length != 0);
if ((unsigned int)best_len <= s->lookahead)
return (unsigned int)best_len;
return s->lookahead;
}
#endif
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