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354 lines
10 KiB
354 lines
10 KiB
/* match.s -- Pentium-optimized version of longest_match() |
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* Written for zlib 1.1.2 |
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* Copyright (C) 1998 Brian Raiter <breadbox@muppetlabs.com> |
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* |
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* This is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License. |
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*/ |
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#ifndef NO_UNDERLINE |
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#define match_init _match_init |
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#define longest_match _longest_match |
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#endif |
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#define MAX_MATCH (258) |
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#define MIN_MATCH (3) |
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#define MIN_LOOKAHEAD (MAX_MATCH + MIN_MATCH + 1) |
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#define MAX_MATCH_8 ((MAX_MATCH + 7) & ~7) |
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/* stack frame offsets */ |
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#define wmask 0 /* local copy of s->wmask */ |
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#define window 4 /* local copy of s->window */ |
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#define windowbestlen 8 /* s->window + bestlen */ |
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#define chainlenscanend 12 /* high word: current chain len */ |
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/* low word: last bytes sought */ |
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#define scanstart 16 /* first two bytes of string */ |
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#define scanalign 20 /* dword-misalignment of string */ |
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#define nicematch 24 /* a good enough match size */ |
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#define bestlen 28 /* size of best match so far */ |
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#define scan 32 /* ptr to string wanting match */ |
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#define LocalVarsSize (36) |
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/* saved ebx 36 */ |
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/* saved edi 40 */ |
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/* saved esi 44 */ |
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/* saved ebp 48 */ |
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/* return address 52 */ |
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#define deflatestate 56 /* the function arguments */ |
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#define curmatch 60 |
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/* Offsets for fields in the deflate_state structure. These numbers |
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* are calculated from the definition of deflate_state, with the |
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* assumption that the compiler will dword-align the fields. (Thus, |
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* changing the definition of deflate_state could easily cause this |
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* program to crash horribly, without so much as a warning at |
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* compile time. Sigh.) |
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*/ |
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#define dsWSize 36 |
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#define dsWMask 44 |
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#define dsWindow 48 |
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#define dsPrev 56 |
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#define dsMatchLen 88 |
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#define dsPrevMatch 92 |
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#define dsStrStart 100 |
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#define dsMatchStart 104 |
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#define dsLookahead 108 |
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#define dsPrevLen 112 |
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#define dsMaxChainLen 116 |
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#define dsGoodMatch 132 |
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#define dsNiceMatch 136 |
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.file "match.S" |
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.globl match_init, longest_match |
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.text |
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/* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */ |
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longest_match: |
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/* Save registers that the compiler may be using, and adjust %esp to */ |
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/* make room for our stack frame. */ |
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pushl %ebp |
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pushl %edi |
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pushl %esi |
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pushl %ebx |
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subl $LocalVarsSize, %esp |
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/* Retrieve the function arguments. %ecx will hold cur_match */ |
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/* throughout the entire function. %edx will hold the pointer to the */ |
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/* deflate_state structure during the function's setup (before */ |
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/* entering the main loop). */ |
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movl deflatestate(%esp), %edx |
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movl curmatch(%esp), %ecx |
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/* if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead; */ |
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movl dsNiceMatch(%edx), %eax |
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movl dsLookahead(%edx), %ebx |
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cmpl %eax, %ebx |
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jl LookaheadLess |
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movl %eax, %ebx |
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LookaheadLess: movl %ebx, nicematch(%esp) |
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/* register Bytef *scan = s->window + s->strstart; */ |
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movl dsWindow(%edx), %esi |
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movl %esi, window(%esp) |
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movl dsStrStart(%edx), %ebp |
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lea (%esi,%ebp), %edi |
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movl %edi, scan(%esp) |
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/* Determine how many bytes the scan ptr is off from being */ |
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/* dword-aligned. */ |
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movl %edi, %eax |
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negl %eax |
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andl $3, %eax |
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movl %eax, scanalign(%esp) |
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/* IPos limit = s->strstart > (IPos)MAX_DIST(s) ? */ |
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/* s->strstart - (IPos)MAX_DIST(s) : NIL; */ |
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movl dsWSize(%edx), %eax |
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subl $MIN_LOOKAHEAD, %eax |
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subl %eax, %ebp |
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jg LimitPositive |
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xorl %ebp, %ebp |
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LimitPositive: |
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/* unsigned chain_length = s->max_chain_length; */ |
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/* if (s->prev_length >= s->good_match) { */ |
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/* chain_length >>= 2; */ |
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/* } */ |
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movl dsPrevLen(%edx), %eax |
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movl dsGoodMatch(%edx), %ebx |
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cmpl %ebx, %eax |
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movl dsMaxChainLen(%edx), %ebx |
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jl LastMatchGood |
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shrl $2, %ebx |
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LastMatchGood: |
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/* chainlen is decremented once beforehand so that the function can */ |
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/* use the sign flag instead of the zero flag for the exit test. */ |
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/* It is then shifted into the high word, to make room for the scanend */ |
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/* scanend value, which it will always accompany. */ |
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decl %ebx |
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shll $16, %ebx |
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/* int best_len = s->prev_length; */ |
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movl dsPrevLen(%edx), %eax |
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movl %eax, bestlen(%esp) |
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/* Store the sum of s->window + best_len in %esi locally, and in %esi. */ |
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addl %eax, %esi |
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movl %esi, windowbestlen(%esp) |
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/* register ush scan_start = *(ushf*)scan; */ |
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/* register ush scan_end = *(ushf*)(scan+best_len-1); */ |
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movw (%edi), %bx |
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movw %bx, scanstart(%esp) |
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movw -1(%edi,%eax), %bx |
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movl %ebx, chainlenscanend(%esp) |
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/* Posf *prev = s->prev; */ |
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/* uInt wmask = s->w_mask; */ |
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movl dsPrev(%edx), %edi |
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movl dsWMask(%edx), %edx |
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mov %edx, wmask(%esp) |
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/* Jump into the main loop. */ |
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jmp LoopEntry |
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.balign 16 |
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/* do { |
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* match = s->window + cur_match; |
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* if (*(ushf*)(match+best_len-1) != scan_end || |
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* *(ushf*)match != scan_start) continue; |
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* [...] |
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* } while ((cur_match = prev[cur_match & wmask]) > limit |
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* && --chain_length != 0); |
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* |
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* Here is the inner loop of the function. The function will spend the |
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* majority of its time in this loop, and majority of that time will |
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* be spent in the first ten instructions. |
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* |
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* Within this loop: |
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* %ebx = chainlenscanend - i.e., ((chainlen << 16) | scanend) |
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* %ecx = curmatch |
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* %edx = curmatch & wmask |
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* %esi = windowbestlen - i.e., (window + bestlen) |
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* %edi = prev |
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* %ebp = limit |
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* |
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* Two optimization notes on the choice of instructions: |
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* |
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* The first instruction uses a 16-bit address, which costs an extra, |
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* unpairable cycle. This is cheaper than doing a 32-bit access and |
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* zeroing the high word, due to the 3-cycle misalignment penalty which |
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* would occur half the time. This also turns out to be cheaper than |
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* doing two separate 8-bit accesses, as the memory is so rarely in the |
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* L1 cache. |
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* |
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* The window buffer, however, apparently spends a lot of time in the |
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* cache, and so it is faster to retrieve the word at the end of the |
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* match string with two 8-bit loads. The instructions that test the |
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* word at the beginning of the match string, however, are executed |
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* much less frequently, and there it was cheaper to use 16-bit |
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* instructions, which avoided the necessity of saving off and |
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* subsequently reloading one of the other registers. |
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*/ |
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LookupLoop: |
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/* 1 U & V */ |
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movw (%edi,%edx,2), %cx /* 2 U pipe */ |
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movl wmask(%esp), %edx /* 2 V pipe */ |
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cmpl %ebp, %ecx /* 3 U pipe */ |
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jbe LeaveNow /* 3 V pipe */ |
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subl $0x00010000, %ebx /* 4 U pipe */ |
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js LeaveNow /* 4 V pipe */ |
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LoopEntry: movb -1(%esi,%ecx), %al /* 5 U pipe */ |
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andl %ecx, %edx /* 5 V pipe */ |
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cmpb %bl, %al /* 6 U pipe */ |
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jnz LookupLoop /* 6 V pipe */ |
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movb (%esi,%ecx), %ah |
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cmpb %bh, %ah |
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jnz LookupLoop |
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movl window(%esp), %eax |
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movw (%eax,%ecx), %ax |
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cmpw scanstart(%esp), %ax |
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jnz LookupLoop |
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/* Store the current value of chainlen. */ |
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movl %ebx, chainlenscanend(%esp) |
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/* Point %edi to the string under scrutiny, and %esi to the string we */ |
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/* are hoping to match it up with. In actuality, %esi and %edi are */ |
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/* both pointed (MAX_MATCH_8 - scanalign) bytes ahead, and %edx is */ |
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/* initialized to -(MAX_MATCH_8 - scanalign). */ |
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movl window(%esp), %esi |
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movl scan(%esp), %edi |
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addl %ecx, %esi |
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movl scanalign(%esp), %eax |
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movl $(-MAX_MATCH_8), %edx |
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lea MAX_MATCH_8(%edi,%eax), %edi |
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lea MAX_MATCH_8(%esi,%eax), %esi |
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/* Test the strings for equality, 8 bytes at a time. At the end, |
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* adjust %edx so that it is offset to the exact byte that mismatched. |
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* |
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* We already know at this point that the first three bytes of the |
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* strings match each other, and they can be safely passed over before |
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* starting the compare loop. So what this code does is skip over 0-3 |
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* bytes, as much as necessary in order to dword-align the %edi |
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* pointer. (%esi will still be misaligned three times out of four.) |
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* |
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* It should be confessed that this loop usually does not represent |
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* much of the total running time. Replacing it with a more |
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* straightforward "rep cmpsb" would not drastically degrade |
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* performance. |
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*/ |
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LoopCmps: |
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movl (%esi,%edx), %eax |
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movl (%edi,%edx), %ebx |
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xorl %ebx, %eax |
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jnz LeaveLoopCmps |
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movl 4(%esi,%edx), %eax |
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movl 4(%edi,%edx), %ebx |
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xorl %ebx, %eax |
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jnz LeaveLoopCmps4 |
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addl $8, %edx |
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jnz LoopCmps |
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jmp LenMaximum |
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LeaveLoopCmps4: addl $4, %edx |
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LeaveLoopCmps: testl $0x0000FFFF, %eax |
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jnz LenLower |
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addl $2, %edx |
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shrl $16, %eax |
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LenLower: subb $1, %al |
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adcl $0, %edx |
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/* Calculate the length of the match. If it is longer than MAX_MATCH, */ |
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/* then automatically accept it as the best possible match and leave. */ |
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lea (%edi,%edx), %eax |
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movl scan(%esp), %edi |
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subl %edi, %eax |
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cmpl $MAX_MATCH, %eax |
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jge LenMaximum |
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/* If the length of the match is not longer than the best match we */ |
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/* have so far, then forget it and return to the lookup loop. */ |
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movl deflatestate(%esp), %edx |
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movl bestlen(%esp), %ebx |
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cmpl %ebx, %eax |
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jg LongerMatch |
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movl chainlenscanend(%esp), %ebx |
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movl windowbestlen(%esp), %esi |
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movl dsPrev(%edx), %edi |
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movl wmask(%esp), %edx |
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andl %ecx, %edx |
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jmp LookupLoop |
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/* s->match_start = cur_match; */ |
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/* best_len = len; */ |
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/* if (len >= nice_match) break; */ |
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/* scan_end = *(ushf*)(scan+best_len-1); */ |
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LongerMatch: movl nicematch(%esp), %ebx |
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movl %eax, bestlen(%esp) |
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movl %ecx, dsMatchStart(%edx) |
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cmpl %ebx, %eax |
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jge LeaveNow |
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movl window(%esp), %esi |
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addl %eax, %esi |
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movl %esi, windowbestlen(%esp) |
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movl chainlenscanend(%esp), %ebx |
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movw -1(%edi,%eax), %bx |
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movl dsPrev(%edx), %edi |
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movl %ebx, chainlenscanend(%esp) |
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movl wmask(%esp), %edx |
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andl %ecx, %edx |
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jmp LookupLoop |
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/* Accept the current string, with the maximum possible length. */ |
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LenMaximum: movl deflatestate(%esp), %edx |
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movl $MAX_MATCH, bestlen(%esp) |
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movl %ecx, dsMatchStart(%edx) |
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/* if ((uInt)best_len <= s->lookahead) return (uInt)best_len; */ |
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/* return s->lookahead; */ |
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LeaveNow: |
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movl deflatestate(%esp), %edx |
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movl bestlen(%esp), %ebx |
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movl dsLookahead(%edx), %eax |
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cmpl %eax, %ebx |
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jg LookaheadRet |
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movl %ebx, %eax |
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LookaheadRet: |
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/* Restore the stack and return from whence we came. */ |
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addl $LocalVarsSize, %esp |
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popl %ebx |
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popl %esi |
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popl %edi |
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popl %ebp |
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match_init: ret
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