/* match.s -- Pentium-optimized version of longest_match() * Written for zlib 1.1.2 * Copyright (C) 1998 Brian Raiter * * 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