+++ /dev/null
-/* 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
projects / silc.git / blobdiff