source: rtems/cpukit/zlib/contrib/amd64/amd64-match.S @ 69f34ca

/*
 * 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.
 */

#ifndef NO_UNDERLINE
#       define  match_init      _match_init
#       define  longest_match   _longest_match
#endif

#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 MIN_LOOKAHEAD   (MAX_MATCH + MIN_MATCH + 1)
#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"
 */


#ifndef CURRENT_LINX_XCODE_MAC_X64_STRUCTURE
#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)

#else 

#ifndef STRUCT_OFFSET
#       define STRUCT_OFFSET    (0)
#endif


#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)

#endif




.text

/* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */

longest_match:
/*
 * 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
LastMatchGood:

/* 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.
 */
LookupLoop:
                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... */

LoopCmps:
#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
#else
                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
LeaveLoopCmps16:
                add     $8, %rdx
LeaveLoopCmps8:
                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
#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);                        */

LongerMatch:
                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.         */

LenMaximum:
                movl    $MAX_MATCH, %bestlend
                movl    %curmatchd, dsMatchStart

/* if ((uInt)best_len <= s->lookahead) return (uInt)best_len;           */
/* return s->lookahead;                                                 */

LeaveNow:
                movl    dsLookahead, %eax
                cmpl    %eax, %bestlend
                cmovngl %bestlend, %eax
LookaheadRet:

/* 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

        ret

match_init:     ret