1/* match.s -- Pentium-Pro-optimized version of longest_match()
2 * Written for zlib 1.1.2
3 * Copyright (C) 1998 Brian Raiter <breadbox@muppetlabs.com>
4 *
5 * This is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License.
7 */
8
9#ifndef NO_UNDERLINE
10#define	match_init	_match_init
11#define	longest_match	_longest_match
12#endif
13
14#define	MAX_MATCH	(258)
15#define	MIN_MATCH	(3)
16#define	MIN_LOOKAHEAD	(MAX_MATCH + MIN_MATCH + 1)
17#define	MAX_MATCH_8	((MAX_MATCH + 7) & ~7)
18
19/* stack frame offsets */
20
21#define	chainlenwmask		0	/* high word: current chain len	*/
22					/* low word: s->wmask		*/
23#define	window			4	/* local copy of s->window	*/
24#define	windowbestlen		8	/* s->window + bestlen		*/
25#define	scanstart		16	/* first two bytes of string	*/
26#define	scanend			12	/* last two bytes of string	*/
27#define	scanalign		20	/* dword-misalignment of string	*/
28#define	nicematch		24	/* a good enough match size	*/
29#define	bestlen			28	/* size of best match so far	*/
30#define	scan			32	/* ptr to string wanting match	*/
31
32#define	LocalVarsSize		(36)
33/*	saved ebx		36 */
34/*	saved edi		40 */
35/*	saved esi		44 */
36/*	saved ebp		48 */
37/*	return address		52 */
38#define	deflatestate		56	/* the function arguments	*/
39#define	curmatch		60
40
41/* All the +zlib1222add offsets are due to the addition of fields
42 *  in zlib in the deflate_state structure since the asm code was first written
43 * (if you compile with zlib 1.0.4 or older, use "zlib1222add equ (-4)").
44 * (if you compile with zlib between 1.0.5 and 1.2.2.1, use "zlib1222add equ 0").
45 * if you compile with zlib 1.2.2.2 or later , use "zlib1222add equ 8").
46 */
47
48#define zlib1222add		(8)
49
50#define	dsWSize			(36+zlib1222add)
51#define	dsWMask			(44+zlib1222add)
52#define	dsWindow		(48+zlib1222add)
53#define	dsPrev			(56+zlib1222add)
54#define	dsMatchLen		(88+zlib1222add)
55#define	dsPrevMatch		(92+zlib1222add)
56#define	dsStrStart		(100+zlib1222add)
57#define	dsMatchStart		(104+zlib1222add)
58#define	dsLookahead		(108+zlib1222add)
59#define	dsPrevLen		(112+zlib1222add)
60#define	dsMaxChainLen		(116+zlib1222add)
61#define	dsGoodMatch		(132+zlib1222add)
62#define	dsNiceMatch		(136+zlib1222add)
63
64
65.file "match.S"
66
67.globl	match_init, longest_match
68
69.text
70
71/* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */
72
73longest_match:
74
75/* Save registers that the compiler may be using, and adjust %esp to	*/
76/* make room for our stack frame.					*/
77
78		pushl	%ebp
79		pushl	%edi
80		pushl	%esi
81		pushl	%ebx
82		subl	$LocalVarsSize, %esp
83
84/* Retrieve the function arguments. %ecx will hold cur_match		*/
85/* throughout the entire function. %edx will hold the pointer to the	*/
86/* deflate_state structure during the function's setup (before		*/
87/* entering the main loop).						*/
88
89		movl	deflatestate(%esp), %edx
90		movl	curmatch(%esp), %ecx
91
92/* uInt wmask = s->w_mask;						*/
93/* unsigned chain_length = s->max_chain_length;				*/
94/* if (s->prev_length >= s->good_match) {				*/
95/*     chain_length >>= 2;						*/
96/* }									*/
97
98		movl	dsPrevLen(%edx), %eax
99		movl	dsGoodMatch(%edx), %ebx
100		cmpl	%ebx, %eax
101		movl	dsWMask(%edx), %eax
102		movl	dsMaxChainLen(%edx), %ebx
103		jl	LastMatchGood
104		shrl	$2, %ebx
105LastMatchGood:
106
107/* chainlen is decremented once beforehand so that the function can	*/
108/* use the sign flag instead of the zero flag for the exit test.	*/
109/* It is then shifted into the high word, to make room for the wmask	*/
110/* value, which it will always accompany.				*/
111
112		decl	%ebx
113		shll	$16, %ebx
114		orl	%eax, %ebx
115		movl	%ebx, chainlenwmask(%esp)
116
117/* if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead;	*/
118
119		movl	dsNiceMatch(%edx), %eax
120		movl	dsLookahead(%edx), %ebx
121		cmpl	%eax, %ebx
122		jl	LookaheadLess
123		movl	%eax, %ebx
124LookaheadLess:	movl	%ebx, nicematch(%esp)
125
126/* register Bytef *scan = s->window + s->strstart;			*/
127
128		movl	dsWindow(%edx), %esi
129		movl	%esi, window(%esp)
130		movl	dsStrStart(%edx), %ebp
131		lea	(%esi,%ebp), %edi
132		movl	%edi, scan(%esp)
133
134/* Determine how many bytes the scan ptr is off from being		*/
135/* dword-aligned.							*/
136
137		movl	%edi, %eax
138		negl	%eax
139		andl	$3, %eax
140		movl	%eax, scanalign(%esp)
141
142/* IPos limit = s->strstart > (IPos)MAX_DIST(s) ?			*/
143/*     s->strstart - (IPos)MAX_DIST(s) : NIL;				*/
144
145		movl	dsWSize(%edx), %eax
146		subl	$MIN_LOOKAHEAD, %eax
147		subl	%eax, %ebp
148		jg	LimitPositive
149		xorl	%ebp, %ebp
150LimitPositive:
151
152/* int best_len = s->prev_length;					*/
153
154		movl	dsPrevLen(%edx), %eax
155		movl	%eax, bestlen(%esp)
156
157/* Store the sum of s->window + best_len in %esi locally, and in %esi.	*/
158
159		addl	%eax, %esi
160		movl	%esi, windowbestlen(%esp)
161
162/* register ush scan_start = *(ushf*)scan;				*/
163/* register ush scan_end   = *(ushf*)(scan+best_len-1);			*/
164/* Posf *prev = s->prev;						*/
165
166		movzwl	(%edi), %ebx
167		movl	%ebx, scanstart(%esp)
168		movzwl	-1(%edi,%eax), %ebx
169		movl	%ebx, scanend(%esp)
170		movl	dsPrev(%edx), %edi
171
172/* Jump into the main loop.						*/
173
174		movl	chainlenwmask(%esp), %edx
175		jmp	LoopEntry
176
177.balign 16
178
179/* do {
180 *     match = s->window + cur_match;
181 *     if (*(ushf*)(match+best_len-1) != scan_end ||
182 *         *(ushf*)match != scan_start) continue;
183 *     [...]
184 * } while ((cur_match = prev[cur_match & wmask]) > limit
185 *          && --chain_length != 0);
186 *
187 * Here is the inner loop of the function. The function will spend the
188 * majority of its time in this loop, and majority of that time will
189 * be spent in the first ten instructions.
190 *
191 * Within this loop:
192 * %ebx = scanend
193 * %ecx = curmatch
194 * %edx = chainlenwmask - i.e., ((chainlen << 16) | wmask)
195 * %esi = windowbestlen - i.e., (window + bestlen)
196 * %edi = prev
197 * %ebp = limit
198 */
199LookupLoop:
200		andl	%edx, %ecx
201		movzwl	(%edi,%ecx,2), %ecx
202		cmpl	%ebp, %ecx
203		jbe	LeaveNow
204		subl	$0x00010000, %edx
205		js	LeaveNow
206LoopEntry:	movzwl	-1(%esi,%ecx), %eax
207		cmpl	%ebx, %eax
208		jnz	LookupLoop
209		movl	window(%esp), %eax
210		movzwl	(%eax,%ecx), %eax
211		cmpl	scanstart(%esp), %eax
212		jnz	LookupLoop
213
214/* Store the current value of chainlen.					*/
215
216		movl	%edx, chainlenwmask(%esp)
217
218/* Point %edi to the string under scrutiny, and %esi to the string we	*/
219/* are hoping to match it up with. In actuality, %esi and %edi are	*/
220/* both pointed (MAX_MATCH_8 - scanalign) bytes ahead, and %edx is	*/
221/* initialized to -(MAX_MATCH_8 - scanalign).				*/
222
223		movl	window(%esp), %esi
224		movl	scan(%esp), %edi
225		addl	%ecx, %esi
226		movl	scanalign(%esp), %eax
227		movl	$(-MAX_MATCH_8), %edx
228		lea	MAX_MATCH_8(%edi,%eax), %edi
229		lea	MAX_MATCH_8(%esi,%eax), %esi
230
231/* Test the strings for equality, 8 bytes at a time. At the end,
232 * adjust %edx so that it is offset to the exact byte that mismatched.
233 *
234 * We already know at this point that the first three bytes of the
235 * strings match each other, and they can be safely passed over before
236 * starting the compare loop. So what this code does is skip over 0-3
237 * bytes, as much as necessary in order to dword-align the %edi
238 * pointer. (%esi will still be misaligned three times out of four.)
239 *
240 * It should be confessed that this loop usually does not represent
241 * much of the total running time. Replacing it with a more
242 * straightforward "rep cmpsb" would not drastically degrade
243 * performance.
244 */
245LoopCmps:
246		movl	(%esi,%edx), %eax
247		xorl	(%edi,%edx), %eax
248		jnz	LeaveLoopCmps
249		movl	4(%esi,%edx), %eax
250		xorl	4(%edi,%edx), %eax
251		jnz	LeaveLoopCmps4
252		addl	$8, %edx
253		jnz	LoopCmps
254		jmp	LenMaximum
255LeaveLoopCmps4:	addl	$4, %edx
256LeaveLoopCmps:	testl	$0x0000FFFF, %eax
257		jnz	LenLower
258		addl	$2, %edx
259		shrl	$16, %eax
260LenLower:	subb	$1, %al
261		adcl	$0, %edx
262
263/* Calculate the length of the match. If it is longer than MAX_MATCH,	*/
264/* then automatically accept it as the best possible match and leave.	*/
265
266		lea	(%edi,%edx), %eax
267		movl	scan(%esp), %edi
268		subl	%edi, %eax
269		cmpl	$MAX_MATCH, %eax
270		jge	LenMaximum
271
272/* If the length of the match is not longer than the best match we	*/
273/* have so far, then forget it and return to the lookup loop.		*/
274
275		movl	deflatestate(%esp), %edx
276		movl	bestlen(%esp), %ebx
277		cmpl	%ebx, %eax
278		jg	LongerMatch
279		movl	windowbestlen(%esp), %esi
280		movl	dsPrev(%edx), %edi
281		movl	scanend(%esp), %ebx
282		movl	chainlenwmask(%esp), %edx
283		jmp	LookupLoop
284
285/*         s->match_start = cur_match;					*/
286/*         best_len = len;						*/
287/*         if (len >= nice_match) break;				*/
288/*         scan_end = *(ushf*)(scan+best_len-1);			*/
289
290LongerMatch:	movl	nicematch(%esp), %ebx
291		movl	%eax, bestlen(%esp)
292		movl	%ecx, dsMatchStart(%edx)
293		cmpl	%ebx, %eax
294		jge	LeaveNow
295		movl	window(%esp), %esi
296		addl	%eax, %esi
297		movl	%esi, windowbestlen(%esp)
298		movzwl	-1(%edi,%eax), %ebx
299		movl	dsPrev(%edx), %edi
300		movl	%ebx, scanend(%esp)
301		movl	chainlenwmask(%esp), %edx
302		jmp	LookupLoop
303
304/* Accept the current string, with the maximum possible length.		*/
305
306LenMaximum:	movl	deflatestate(%esp), %edx
307		movl	$MAX_MATCH, bestlen(%esp)
308		movl	%ecx, dsMatchStart(%edx)
309
310/* if ((uInt)best_len <= s->lookahead) return (uInt)best_len;		*/
311/* return s->lookahead;							*/
312
313LeaveNow:
314		movl	deflatestate(%esp), %edx
315		movl	bestlen(%esp), %ebx
316		movl	dsLookahead(%edx), %eax
317		cmpl	%eax, %ebx
318		jg	LookaheadRet
319		movl	%ebx, %eax
320LookaheadRet:
321
322/* Restore the stack and return from whence we came.			*/
323
324		addl	$LocalVarsSize, %esp
325		popl	%ebx
326		popl	%esi
327		popl	%edi
328		popl	%ebp
329match_init:	ret
330