/* 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.)

 */

/* 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