/* 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, %ebxLookaheadLess:	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, %ebpLimitPositive:/* 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, %ebxLastMatchGood:/* 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	LenMaximumLeaveLoopCmps4:	addl	$4, %edxLeaveLoopCmps:	testl	$0x0000FFFF, %eax		jnz	LenLower		addl	$2, %edx		shrl	$16, %eaxLenLower:	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, %eaxLookaheadRet:/* Restore the stack and return from whence we came.			*/		addl	$LocalVarsSize, %esp		popl	%ebx		popl	%esi		popl	%edi		popl	%ebpmatch_init:	ret