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* match.S -- optimized version of longest_match()
* based on the similar work by Gilles Vollant, and Brian Raiter, written 1998
* This is free software; you can redistribute it and/or modify it
* under the terms of the BSD License. Use by owners of Che Guevarra
* parafernalia is prohibited, where possible, and highly discouraged
* elsewhere.
# define match_init _match_init
# define longest_match _longest_match
#define scanend ebx
#define scanendw bx
#define chainlenwmask edx /* high word: current chain len low word: s->wmask */
#define curmatch rsi
#define curmatchd esi
#define windowbestlen r8
#define scanalign r9
#define scanalignd r9d
#define window r10
#define bestlen r11
#define bestlend r11d
#define scanstart r12d
#define scanstartw r12w
#define scan r13
#define nicematch r14d
#define limit r15
#define limitd r15d
#define prev rcx
* The 258 is a "magic number, not a parameter -- changing it
* breaks the hell loose
#define MAX_MATCH (258)
#define MIN_MATCH (3)
#define MAX_MATCH_8 ((MAX_MATCH + 7) & ~7)
/* stack frame offsets */
#define LocalVarsSize (112)
#define _chainlenwmask ( 8-LocalVarsSize)(%rsp)
#define _windowbestlen (16-LocalVarsSize)(%rsp)
#define save_r14 (24-LocalVarsSize)(%rsp)
#define save_rsi (32-LocalVarsSize)(%rsp)
#define save_rbx (40-LocalVarsSize)(%rsp)
#define save_r12 (56-LocalVarsSize)(%rsp)
#define save_r13 (64-LocalVarsSize)(%rsp)
#define save_r15 (80-LocalVarsSize)(%rsp)
.globl match_init, longest_match
* On AMD64 the first argument of a function (in our case -- the pointer to
* deflate_state structure) is passed in %rdi, hence our offsets below are
* all off of that.
/* you can check the structure offset by running
#include <stdlib.h>
#include <stdio.h>
#include "deflate.h"
void print_depl()
deflate_state ds;
deflate_state *s=&ds;
printf("size pointer=%u\n",(int)sizeof(void*));
printf("#define dsWSize (%3u)(%%rdi)\n",(int)(((char*)&(s->w_size))-((char*)s)));
printf("#define dsWMask (%3u)(%%rdi)\n",(int)(((char*)&(s->w_mask))-((char*)s)));
printf("#define dsWindow (%3u)(%%rdi)\n",(int)(((char*)&(s->window))-((char*)s)));
printf("#define dsPrev (%3u)(%%rdi)\n",(int)(((char*)&(s->prev))-((char*)s)));
printf("#define dsMatchLen (%3u)(%%rdi)\n",(int)(((char*)&(s->match_length))-((char*)s)));
printf("#define dsPrevMatch (%3u)(%%rdi)\n",(int)(((char*)&(s->prev_match))-((char*)s)));
printf("#define dsStrStart (%3u)(%%rdi)\n",(int)(((char*)&(s->strstart))-((char*)s)));
printf("#define dsMatchStart (%3u)(%%rdi)\n",(int)(((char*)&(s->match_start))-((char*)s)));
printf("#define dsLookahead (%3u)(%%rdi)\n",(int)(((char*)&(s->lookahead))-((char*)s)));
printf("#define dsPrevLen (%3u)(%%rdi)\n",(int)(((char*)&(s->prev_length))-((char*)s)));
printf("#define dsMaxChainLen (%3u)(%%rdi)\n",(int)(((char*)&(s->max_chain_length))-((char*)s)));
printf("#define dsGoodMatch (%3u)(%%rdi)\n",(int)(((char*)&(s->good_match))-((char*)s)));
printf("#define dsNiceMatch (%3u)(%%rdi)\n",(int)(((char*)&(s->nice_match))-((char*)s)));
to compile for XCode 3.2 on MacOSX x86_64
- run "gcc -g -c -DXCODE_MAC_X64_STRUCTURE amd64-match.S"
#define dsWSize ( 68)(%rdi)
#define dsWMask ( 76)(%rdi)
#define dsWindow ( 80)(%rdi)
#define dsPrev ( 96)(%rdi)
#define dsMatchLen (144)(%rdi)
#define dsPrevMatch (148)(%rdi)
#define dsStrStart (156)(%rdi)
#define dsMatchStart (160)(%rdi)
#define dsLookahead (164)(%rdi)
#define dsPrevLen (168)(%rdi)
#define dsMaxChainLen (172)(%rdi)
#define dsGoodMatch (188)(%rdi)
#define dsNiceMatch (192)(%rdi)
# define STRUCT_OFFSET (0)
#define dsWSize ( 56 + STRUCT_OFFSET)(%rdi)
#define dsWMask ( 64 + STRUCT_OFFSET)(%rdi)
#define dsWindow ( 72 + STRUCT_OFFSET)(%rdi)
#define dsPrev ( 88 + STRUCT_OFFSET)(%rdi)
#define dsMatchLen (136 + STRUCT_OFFSET)(%rdi)
#define dsPrevMatch (140 + STRUCT_OFFSET)(%rdi)
#define dsStrStart (148 + STRUCT_OFFSET)(%rdi)
#define dsMatchStart (152 + STRUCT_OFFSET)(%rdi)
#define dsLookahead (156 + STRUCT_OFFSET)(%rdi)
#define dsPrevLen (160 + STRUCT_OFFSET)(%rdi)
#define dsMaxChainLen (164 + STRUCT_OFFSET)(%rdi)
#define dsGoodMatch (180 + STRUCT_OFFSET)(%rdi)
#define dsNiceMatch (184 + STRUCT_OFFSET)(%rdi)
/* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */
* Retrieve the function arguments. %curmatch will hold cur_match
* throughout the entire function (passed via rsi on amd64).
* rdi will hold the pointer to the deflate_state (first arg on amd64)
mov %rsi, save_rsi
mov %rbx, save_rbx
mov %r12, save_r12
mov %r13, save_r13
mov %r14, save_r14
mov %r15, save_r15
/* uInt wmask = s->w_mask; */
/* unsigned chain_length = s->max_chain_length; */
/* if (s->prev_length >= s->good_match) { */
/* chain_length >>= 2; */
/* } */
movl dsPrevLen, %eax
movl dsGoodMatch, %ebx
cmpl %ebx, %eax
movl dsWMask, %eax
movl dsMaxChainLen, %chainlenwmask
jl LastMatchGood
shrl $2, %chainlenwmask
/* chainlen is decremented once beforehand so that the function can */
/* use the sign flag instead of the zero flag for the exit test. */
/* It is then shifted into the high word, to make room for the wmask */
/* value, which it will always accompany. */
decl %chainlenwmask
shll $16, %chainlenwmask
orl %eax, %chainlenwmask
/* if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead; */
movl dsNiceMatch, %eax
movl dsLookahead, %ebx
cmpl %eax, %ebx
jl LookaheadLess
movl %eax, %ebx
LookaheadLess: movl %ebx, %nicematch
/* register Bytef *scan = s->window + s->strstart; */
mov dsWindow, %window
movl dsStrStart, %limitd
lea (%limit, %window), %scan
/* Determine how many bytes the scan ptr is off from being */
/* dword-aligned. */
mov %scan, %scanalign
negl %scanalignd
andl $3, %scanalignd
/* IPos limit = s->strstart > (IPos)MAX_DIST(s) ? */
/* s->strstart - (IPos)MAX_DIST(s) : NIL; */
movl dsWSize, %eax
subl $MIN_LOOKAHEAD, %eax
xorl %ecx, %ecx
subl %eax, %limitd
cmovng %ecx, %limitd
/* int best_len = s->prev_length; */
movl dsPrevLen, %bestlend
/* Store the sum of s->window + best_len in %windowbestlen locally, and in memory. */
lea (%window, %bestlen), %windowbestlen
mov %windowbestlen, _windowbestlen
/* register ush scan_start = *(ushf*)scan; */
/* register ush scan_end = *(ushf*)(scan+best_len-1); */
/* Posf *prev = s->prev; */
movzwl (%scan), %scanstart
movzwl -1(%scan, %bestlen), %scanend
mov dsPrev, %prev
/* Jump into the main loop. */
movl %chainlenwmask, _chainlenwmask
jmp LoopEntry
.balign 16
/* do {
* match = s->window + cur_match;
* if (*(ushf*)(match+best_len-1) != scan_end ||
* *(ushf*)match != scan_start) continue;
* [...]
* } while ((cur_match = prev[cur_match & wmask]) > limit
* && --chain_length != 0);
* Here is the inner loop of the function. The function will spend the
* majority of its time in this loop, and majority of that time will
* be spent in the first ten instructions.
andl %chainlenwmask, %curmatchd
movzwl (%prev, %curmatch, 2), %curmatchd
cmpl %limitd, %curmatchd
jbe LeaveNow
subl $0x00010000, %chainlenwmask
js LeaveNow
LoopEntry: cmpw -1(%windowbestlen, %curmatch), %scanendw
jne LookupLoop
cmpw %scanstartw, (%window, %curmatch)
jne LookupLoop
/* Store the current value of chainlen. */
movl %chainlenwmask, _chainlenwmask
/* %scan is the string under scrutiny, and %prev to the string we */
/* are hoping to match it up with. In actuality, %esi and %edi are */
/* both pointed (MAX_MATCH_8 - scanalign) bytes ahead, and %edx is */
/* initialized to -(MAX_MATCH_8 - scanalign). */
mov $(-MAX_MATCH_8), %rdx
lea (%curmatch, %window), %windowbestlen
lea MAX_MATCH_8(%windowbestlen, %scanalign), %windowbestlen
lea MAX_MATCH_8(%scan, %scanalign), %prev
/* the prefetching below makes very little difference... */
prefetcht1 (%windowbestlen, %rdx)
prefetcht1 (%prev, %rdx)
* Test the strings for equality, 8 bytes at a time. At the end,
* adjust %rdx so that it is offset to the exact byte that mismatched.
* It should be confessed that this loop usually does not represent
* much of the total running time. Replacing it with a more
* straightforward "rep cmpsb" would not drastically degrade
* performance -- unrolling it, for example, makes no difference.
#undef USE_SSE /* works, but is 6-7% slower, than non-SSE... */
#ifdef USE_SSE
/* Preload the SSE registers */
movdqu (%windowbestlen, %rdx), %xmm1
movdqu (%prev, %rdx), %xmm2
pcmpeqb %xmm2, %xmm1
movdqu 16(%windowbestlen, %rdx), %xmm3
movdqu 16(%prev, %rdx), %xmm4
pcmpeqb %xmm4, %xmm3
movdqu 32(%windowbestlen, %rdx), %xmm5
movdqu 32(%prev, %rdx), %xmm6
pcmpeqb %xmm6, %xmm5
movdqu 48(%windowbestlen, %rdx), %xmm7
movdqu 48(%prev, %rdx), %xmm8
pcmpeqb %xmm8, %xmm7
/* Check the comparisions' results */
pmovmskb %xmm1, %rax
notw %ax
bsfw %ax, %ax
jnz LeaveLoopCmps
/* this is the only iteration of the loop with a possibility of having
incremented rdx by 0x108 (each loop iteration add 16*4 = 0x40
and (0x40*4)+8=0x108 */
add $8, %rdx
jz LenMaximum
add $8, %rdx
pmovmskb %xmm3, %rax
notw %ax
bsfw %ax, %ax
jnz LeaveLoopCmps
add $16, %rdx
pmovmskb %xmm5, %rax
notw %ax
bsfw %ax, %ax
jnz LeaveLoopCmps
add $16, %rdx
pmovmskb %xmm7, %rax
notw %ax
bsfw %ax, %ax
jnz LeaveLoopCmps
add $16, %rdx
jmp LoopCmps
LeaveLoopCmps: add %rax, %rdx
mov (%windowbestlen, %rdx), %rax
xor (%prev, %rdx), %rax
jnz LeaveLoopCmps
mov 8(%windowbestlen, %rdx), %rax
xor 8(%prev, %rdx), %rax
jnz LeaveLoopCmps8
mov 16(%windowbestlen, %rdx), %rax
xor 16(%prev, %rdx), %rax
jnz LeaveLoopCmps16
add $24, %rdx
jnz LoopCmps
jmp LenMaximum
# if 0
* This three-liner is tantalizingly simple, but bsf is a slow instruction,
* and the complicated alternative down below is quite a bit faster. Sad...
LeaveLoopCmps: bsf %rax, %rax /* find the first non-zero bit */
shrl $3, %eax /* divide by 8 to get the byte */
add %rax, %rdx
# else
add $8, %rdx
add $8, %rdx
LeaveLoopCmps: testl $0xFFFFFFFF, %eax /* Check the first 4 bytes */
jnz Check16
add $4, %rdx
shr $32, %rax
Check16: testw $0xFFFF, %ax
jnz LenLower
add $2, %rdx
shrl $16, %eax
LenLower: subb $1, %al
adc $0, %rdx
# endif
/* Calculate the length of the match. If it is longer than MAX_MATCH, */
/* then automatically accept it as the best possible match and leave. */
lea (%prev, %rdx), %rax
sub %scan, %rax
cmpl $MAX_MATCH, %eax
jge LenMaximum
/* If the length of the match is not longer than the best match we */
/* have so far, then forget it and return to the lookup loop. */
cmpl %bestlend, %eax
jg LongerMatch
mov _windowbestlen, %windowbestlen
mov dsPrev, %prev
movl _chainlenwmask, %edx
jmp LookupLoop
/* s->match_start = cur_match; */
/* best_len = len; */
/* if (len >= nice_match) break; */
/* scan_end = *(ushf*)(scan+best_len-1); */
movl %eax, %bestlend
movl %curmatchd, dsMatchStart
cmpl %nicematch, %eax
jge LeaveNow
lea (%window, %bestlen), %windowbestlen
mov %windowbestlen, _windowbestlen
movzwl -1(%scan, %rax), %scanend
mov dsPrev, %prev
movl _chainlenwmask, %chainlenwmask
jmp LookupLoop
/* Accept the current string, with the maximum possible length. */
movl $MAX_MATCH, %bestlend
movl %curmatchd, dsMatchStart
/* if ((uInt)best_len <= s->lookahead) return (uInt)best_len; */
/* return s->lookahead; */
movl dsLookahead, %eax
cmpl %eax, %bestlend
cmovngl %bestlend, %eax
/* Restore the registers and return from whence we came. */
mov save_rsi, %rsi
mov save_rbx, %rbx
mov save_r12, %r12
mov save_r13, %r13
mov save_r14, %r14
mov save_r15, %r15
match_init: ret