| /* match.s -- Pentium-optimized version of longest_match() |
| * Written for zlib 1.1.2 |
| * Copyright (C) 1998 Brian Raiter <breadbox@muppetlabs.com> |
| * |
| * This is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License. |
| */ |
| |
| #ifndef NO_UNDERLINE |
| #define match_init _match_init |
| #define longest_match _longest_match |
| #endif |
| |
| #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 wmask 0 /* local copy of s->wmask */ |
| #define window 4 /* local copy of s->window */ |
| #define windowbestlen 8 /* s->window + bestlen */ |
| #define chainlenscanend 12 /* high word: current chain len */ |
| /* low word: last bytes sought */ |
| #define scanstart 16 /* first two bytes of string */ |
| #define scanalign 20 /* dword-misalignment of string */ |
| #define nicematch 24 /* a good enough match size */ |
| #define bestlen 28 /* size of best match so far */ |
| #define scan 32 /* ptr to string wanting match */ |
| |
| #define LocalVarsSize (36) |
| /* saved ebx 36 */ |
| /* saved edi 40 */ |
| /* saved esi 44 */ |
| /* saved ebp 48 */ |
| /* return address 52 */ |
| #define deflatestate 56 /* the function arguments */ |
| #define curmatch 60 |
| |
| /* Offsets for fields in the deflate_state structure. These numbers |
| * are calculated from the definition of deflate_state, with the |
| * assumption that the compiler will dword-align the fields. (Thus, |
| * changing the definition of deflate_state could easily cause this |
| * program to crash horribly, without so much as a warning at |
| * compile time. Sigh.) |
| */ |
| |
| /* All the +zlib1222add offsets are due to the addition of fields |
| * in zlib in the deflate_state structure since the asm code was first written |
| * (if you compile with zlib 1.0.4 or older, use "zlib1222add equ (-4)"). |
| * (if you compile with zlib between 1.0.5 and 1.2.2.1, use "zlib1222add equ 0"). |
| * if you compile with zlib 1.2.2.2 or later , use "zlib1222add equ 8"). |
| */ |
| |
| #define zlib1222add (8) |
| |
| #define dsWSize (36+zlib1222add) |
| #define dsWMask (44+zlib1222add) |
| #define dsWindow (48+zlib1222add) |
| #define dsPrev (56+zlib1222add) |
| #define dsMatchLen (88+zlib1222add) |
| #define dsPrevMatch (92+zlib1222add) |
| #define dsStrStart (100+zlib1222add) |
| #define dsMatchStart (104+zlib1222add) |
| #define dsLookahead (108+zlib1222add) |
| #define dsPrevLen (112+zlib1222add) |
| #define dsMaxChainLen (116+zlib1222add) |
| #define dsGoodMatch (132+zlib1222add) |
| #define dsNiceMatch (136+zlib1222add) |
| |
| |
| .file "match.S" |
| |
| .globl match_init, longest_match |
| |
| .text |
| |
| /* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */ |
| |
| longest_match: |
| |
| /* Save registers that the compiler may be using, and adjust %esp to */ |
| /* make room for our stack frame. */ |
| |
| pushl %ebp |
| pushl %edi |
| pushl %esi |
| pushl %ebx |
| subl $LocalVarsSize, %esp |
| |
| /* Retrieve the function arguments. %ecx will hold cur_match */ |
| /* throughout the entire function. %edx will hold the pointer to the */ |
| /* deflate_state structure during the function's setup (before */ |
| /* entering the main loop). */ |
| |
| movl deflatestate(%esp), %edx |
| movl curmatch(%esp), %ecx |
| |
| /* if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead; */ |
| |
| movl dsNiceMatch(%edx), %eax |
| movl dsLookahead(%edx), %ebx |
| cmpl %eax, %ebx |
| jl LookaheadLess |
| movl %eax, %ebx |
| LookaheadLess: movl %ebx, nicematch(%esp) |
| |
| /* register Bytef *scan = s->window + s->strstart; */ |
| |
| movl dsWindow(%edx), %esi |
| movl %esi, window(%esp) |
| movl dsStrStart(%edx), %ebp |
| lea (%esi,%ebp), %edi |
| movl %edi, scan(%esp) |
| |
| /* Determine how many bytes the scan ptr is off from being */ |
| /* dword-aligned. */ |
| |
| movl %edi, %eax |
| negl %eax |
| andl $3, %eax |
| movl %eax, scanalign(%esp) |
| |
| /* IPos limit = s->strstart > (IPos)MAX_DIST(s) ? */ |
| /* s->strstart - (IPos)MAX_DIST(s) : NIL; */ |
| |
| movl dsWSize(%edx), %eax |
| subl $MIN_LOOKAHEAD, %eax |
| subl %eax, %ebp |
| jg LimitPositive |
| xorl %ebp, %ebp |
| LimitPositive: |
| |
| /* unsigned chain_length = s->max_chain_length; */ |
| /* if (s->prev_length >= s->good_match) { */ |
| /* chain_length >>= 2; */ |
| /* } */ |
| |
| movl dsPrevLen(%edx), %eax |
| movl dsGoodMatch(%edx), %ebx |
| cmpl %ebx, %eax |
| movl dsMaxChainLen(%edx), %ebx |
| jl LastMatchGood |
| shrl $2, %ebx |
| 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 scanend */ |
| /* scanend value, which it will always accompany. */ |
| |
| decl %ebx |
| shll $16, %ebx |
| |
| /* int best_len = s->prev_length; */ |
| |
| movl dsPrevLen(%edx), %eax |
| movl %eax, bestlen(%esp) |
| |
| /* Store the sum of s->window + best_len in %esi locally, and in %esi. */ |
| |
| addl %eax, %esi |
| movl %esi, windowbestlen(%esp) |
| |
| /* register ush scan_start = *(ushf*)scan; */ |
| /* register ush scan_end = *(ushf*)(scan+best_len-1); */ |
| |
| movw (%edi), %bx |
| movw %bx, scanstart(%esp) |
| movw -1(%edi,%eax), %bx |
| movl %ebx, chainlenscanend(%esp) |
| |
| /* Posf *prev = s->prev; */ |
| /* uInt wmask = s->w_mask; */ |
| |
| movl dsPrev(%edx), %edi |
| movl dsWMask(%edx), %edx |
| mov %edx, wmask(%esp) |
| |
| /* Jump into the main loop. */ |
| |
| 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. |
| * |
| * Within this loop: |
| * %ebx = chainlenscanend - i.e., ((chainlen << 16) | scanend) |
| * %ecx = curmatch |
| * %edx = curmatch & wmask |
| * %esi = windowbestlen - i.e., (window + bestlen) |
| * %edi = prev |
| * %ebp = limit |
| * |
| * Two optimization notes on the choice of instructions: |
| * |
| * The first instruction uses a 16-bit address, which costs an extra, |
| * unpairable cycle. This is cheaper than doing a 32-bit access and |
| * zeroing the high word, due to the 3-cycle misalignment penalty which |
| * would occur half the time. This also turns out to be cheaper than |
| * doing two separate 8-bit accesses, as the memory is so rarely in the |
| * L1 cache. |
| * |
| * The window buffer, however, apparently spends a lot of time in the |
| * cache, and so it is faster to retrieve the word at the end of the |
| * match string with two 8-bit loads. The instructions that test the |
| * word at the beginning of the match string, however, are executed |
| * much less frequently, and there it was cheaper to use 16-bit |
| * instructions, which avoided the necessity of saving off and |
| * subsequently reloading one of the other registers. |
| */ |
| LookupLoop: |
| /* 1 U & V */ |
| movw (%edi,%edx,2), %cx /* 2 U pipe */ |
| movl wmask(%esp), %edx /* 2 V pipe */ |
| cmpl %ebp, %ecx /* 3 U pipe */ |
| jbe LeaveNow /* 3 V pipe */ |
| subl $0x00010000, %ebx /* 4 U pipe */ |
| js LeaveNow /* 4 V pipe */ |
| LoopEntry: movb -1(%esi,%ecx), %al /* 5 U pipe */ |
| andl %ecx, %edx /* 5 V pipe */ |
| cmpb %bl, %al /* 6 U pipe */ |
| jnz LookupLoop /* 6 V pipe */ |
| movb (%esi,%ecx), %ah |
| cmpb %bh, %ah |
| jnz LookupLoop |
| movl window(%esp), %eax |
| movw (%eax,%ecx), %ax |
| cmpw scanstart(%esp), %ax |
| jnz LookupLoop |
| |
| /* Store the current value of chainlen. */ |
| |
| movl %ebx, chainlenscanend(%esp) |
| |
| /* Point %edi to the string under scrutiny, and %esi 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). */ |
| |
| movl window(%esp), %esi |
| movl scan(%esp), %edi |
| addl %ecx, %esi |
| movl scanalign(%esp), %eax |
| movl $(-MAX_MATCH_8), %edx |
| lea MAX_MATCH_8(%edi,%eax), %edi |
| lea MAX_MATCH_8(%esi,%eax), %esi |
| |
| /* Test the strings for equality, 8 bytes at a time. At the end, |
| * adjust %edx so that it is offset to the exact byte that mismatched. |
| * |
| * We already know at this point that the first three bytes of the |
| * strings match each other, and they can be safely passed over before |
| * starting the compare loop. So what this code does is skip over 0-3 |
| * bytes, as much as necessary in order to dword-align the %edi |
| * pointer. (%esi will still be misaligned three times out of four.) |
| * |
| * 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. |
| */ |
| LoopCmps: |
| movl (%esi,%edx), %eax |
| movl (%edi,%edx), %ebx |
| xorl %ebx, %eax |
| jnz LeaveLoopCmps |
| movl 4(%esi,%edx), %eax |
| movl 4(%edi,%edx), %ebx |
| xorl %ebx, %eax |
| jnz LeaveLoopCmps4 |
| addl $8, %edx |
| jnz LoopCmps |
| jmp LenMaximum |
| LeaveLoopCmps4: addl $4, %edx |
| LeaveLoopCmps: testl $0x0000FFFF, %eax |
| jnz LenLower |
| addl $2, %edx |
| shrl $16, %eax |
| LenLower: subb $1, %al |
| adcl $0, %edx |
| |
| /* 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 (%edi,%edx), %eax |
| movl scan(%esp), %edi |
| subl %edi, %eax |
| 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. */ |
| |
| movl deflatestate(%esp), %edx |
| movl bestlen(%esp), %ebx |
| cmpl %ebx, %eax |
| jg LongerMatch |
| movl chainlenscanend(%esp), %ebx |
| movl windowbestlen(%esp), %esi |
| movl dsPrev(%edx), %edi |
| movl wmask(%esp), %edx |
| andl %ecx, %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 nicematch(%esp), %ebx |
| movl %eax, bestlen(%esp) |
| movl %ecx, dsMatchStart(%edx) |
| cmpl %ebx, %eax |
| jge LeaveNow |
| movl window(%esp), %esi |
| addl %eax, %esi |
| movl %esi, windowbestlen(%esp) |
| movl chainlenscanend(%esp), %ebx |
| movw -1(%edi,%eax), %bx |
| movl dsPrev(%edx), %edi |
| movl %ebx, chainlenscanend(%esp) |
| movl wmask(%esp), %edx |
| andl %ecx, %edx |
| jmp LookupLoop |
| |
| /* Accept the current string, with the maximum possible length. */ |
| |
| LenMaximum: movl deflatestate(%esp), %edx |
| movl $MAX_MATCH, bestlen(%esp) |
| movl %ecx, dsMatchStart(%edx) |
| |
| /* if ((uInt)best_len <= s->lookahead) return (uInt)best_len; */ |
| /* return s->lookahead; */ |
| |
| LeaveNow: |
| movl deflatestate(%esp), %edx |
| movl bestlen(%esp), %ebx |
| movl dsLookahead(%edx), %eax |
| cmpl %eax, %ebx |
| jg LookaheadRet |
| movl %ebx, %eax |
| LookaheadRet: |
| |
| /* Restore the stack and return from whence we came. */ |
| |
| addl $LocalVarsSize, %esp |
| popl %ebx |
| popl %esi |
| popl %edi |
| popl %ebp |
| match_init: ret |
