diff options
Diffstat (limited to 'zlib-1.1.4/contrib/asm586/match.S')
| -rw-r--r-- | zlib-1.1.4/contrib/asm586/match.S | 354 |
1 files changed, 354 insertions, 0 deletions
diff --git a/zlib-1.1.4/contrib/asm586/match.S b/zlib-1.1.4/contrib/asm586/match.S new file mode 100644 index 0000000..8f16140 --- /dev/null +++ b/zlib-1.1.4/contrib/asm586/match.S @@ -0,0 +1,354 @@ +/* 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.) + */ +#define dsWSize 36 +#define dsWMask 44 +#define dsWindow 48 +#define dsPrev 56 +#define dsMatchLen 88 +#define dsPrevMatch 92 +#define dsStrStart 100 +#define dsMatchStart 104 +#define dsLookahead 108 +#define dsPrevLen 112 +#define dsMaxChainLen 116 +#define dsGoodMatch 132 +#define dsNiceMatch 136 + + +.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 |