1/* match.S -- x86 assembly version of the zlib longest_match() function.
  2 * Optimized for the Intel 686 chips (PPro and later).
  3 *
  4 * Copyright (C) 1998, 2007 Brian Raiter <breadbox@muppetlabs.com>
  5 *
  6 * This software is provided 'as-is', without any express or implied
  7 * warranty.  In no event will the author be held liable for any damages
  8 * arising from the use of this software.
  9 *
 10 * Permission is granted to anyone to use this software for any purpose,
 11 * including commercial applications, and to alter it and redistribute it
 12 * freely, subject to the following restrictions:
 13 *
 14 * 1. The origin of this software must not be misrepresented; you must not
 15 *    claim that you wrote the original software. If you use this software
 16 *    in a product, an acknowledgment in the product documentation would be
 17 *    appreciated but is not required.
 18 * 2. Altered source versions must be plainly marked as such, and must not be
 19 *    misrepresented as being the original software.
 20 * 3. This notice may not be removed or altered from any source distribution.
 21 */
 22
 23#ifndef NO_UNDERLINE
 24#define	match_init	_match_init
 25#define	longest_match	_longest_match
 26#endif
 27
 28#define	MAX_MATCH	(258)
 29#define	MIN_MATCH	(3)
 30#define	MIN_LOOKAHEAD	(MAX_MATCH + MIN_MATCH + 1)
 31#define	MAX_MATCH_8	((MAX_MATCH + 7) & ~7)
 32
 33/* stack frame offsets */
 34
 35#define	chainlenwmask		0	/* high word: current chain len	*/
 36					/* low word: s->wmask		*/
 37#define	window			4	/* local copy of s->window	*/
 38#define	windowbestlen		8	/* s->window + bestlen		*/
 39#define	scanstart		16	/* first two bytes of string	*/
 40#define	scanend			12	/* last two bytes of string	*/
 41#define	scanalign		20	/* dword-misalignment of string	*/
 42#define	nicematch		24	/* a good enough match size	*/
 43#define	bestlen			28	/* size of best match so far	*/
 44#define	scan			32	/* ptr to string wanting match	*/
 45
 46#define	LocalVarsSize		(36)
 47/*	saved ebx		36 */
 48/*	saved edi		40 */
 49/*	saved esi		44 */
 50/*	saved ebp		48 */
 51/*	return address		52 */
 52#define	deflatestate		56	/* the function arguments	*/
 53#define	curmatch		60
 54
 55/* All the +zlib1222add offsets are due to the addition of fields
 56 *  in zlib in the deflate_state structure since the asm code was first written
 57 * (if you compile with zlib 1.0.4 or older, use "zlib1222add equ (-4)").
 58 * (if you compile with zlib between 1.0.5 and 1.2.2.1, use "zlib1222add equ 0").
 59 * if you compile with zlib 1.2.2.2 or later , use "zlib1222add equ 8").
 60 */
 61
 62#define zlib1222add		(8)
 63
 64#define	dsWSize			(36+zlib1222add)
 65#define	dsWMask			(44+zlib1222add)
 66#define	dsWindow		(48+zlib1222add)
 67#define	dsPrev			(56+zlib1222add)
 68#define	dsMatchLen		(88+zlib1222add)
 69#define	dsPrevMatch		(92+zlib1222add)
 70#define	dsStrStart		(100+zlib1222add)
 71#define	dsMatchStart		(104+zlib1222add)
 72#define	dsLookahead		(108+zlib1222add)
 73#define	dsPrevLen		(112+zlib1222add)
 74#define	dsMaxChainLen		(116+zlib1222add)
 75#define	dsGoodMatch		(132+zlib1222add)
 76#define	dsNiceMatch		(136+zlib1222add)
 77
 78
 79.file "match.S"
 80
 81.globl	match_init, longest_match
 82
 83.text
 84
 85/* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */
 86.cfi_sections	.debug_frame
 87
 88longest_match:
 89
 90.cfi_startproc
 91/* Save registers that the compiler may be using, and adjust %esp to	*/
 92/* make room for our stack frame.					*/
 93
 94		pushl	%ebp
 95		.cfi_def_cfa_offset 8
 96		.cfi_offset ebp, -8
 97		pushl	%edi
 98		.cfi_def_cfa_offset 12
 99		pushl	%esi
100		.cfi_def_cfa_offset 16
101		pushl	%ebx
102		.cfi_def_cfa_offset 20
103		subl	$LocalVarsSize, %esp
104		.cfi_def_cfa_offset LocalVarsSize+20
105
106/* Retrieve the function arguments. %ecx will hold cur_match		*/
107/* throughout the entire function. %edx will hold the pointer to the	*/
108/* deflate_state structure during the function's setup (before		*/
109/* entering the main loop).						*/
110
111		movl	deflatestate(%esp), %edx
112		movl	curmatch(%esp), %ecx
113
114/* uInt wmask = s->w_mask;						*/
115/* unsigned chain_length = s->max_chain_length;				*/
116/* if (s->prev_length >= s->good_match) {				*/
117/*     chain_length >>= 2;						*/
118/* }									*/
119 
120		movl	dsPrevLen(%edx), %eax
121		movl	dsGoodMatch(%edx), %ebx
122		cmpl	%ebx, %eax
123		movl	dsWMask(%edx), %eax
124		movl	dsMaxChainLen(%edx), %ebx
125		jl	LastMatchGood
126		shrl	$2, %ebx
127LastMatchGood:
128
129/* chainlen is decremented once beforehand so that the function can	*/
130/* use the sign flag instead of the zero flag for the exit test.	*/
131/* It is then shifted into the high word, to make room for the wmask	*/
132/* value, which it will always accompany.				*/
133
134		decl	%ebx
135		shll	$16, %ebx
136		orl	%eax, %ebx
137		movl	%ebx, chainlenwmask(%esp)
138
139/* if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead;	*/
140
141		movl	dsNiceMatch(%edx), %eax
142		movl	dsLookahead(%edx), %ebx
143		cmpl	%eax, %ebx
144		jl	LookaheadLess
145		movl	%eax, %ebx
146LookaheadLess:	movl	%ebx, nicematch(%esp)
147
148/* register Bytef *scan = s->window + s->strstart;			*/
149
150		movl	dsWindow(%edx), %esi
151		movl	%esi, window(%esp)
152		movl	dsStrStart(%edx), %ebp
153		lea	(%esi,%ebp), %edi
154		movl	%edi, scan(%esp)
155
156/* Determine how many bytes the scan ptr is off from being		*/
157/* dword-aligned.							*/
158
159		movl	%edi, %eax
160		negl	%eax
161		andl	$3, %eax
162		movl	%eax, scanalign(%esp)
163
164/* IPos limit = s->strstart > (IPos)MAX_DIST(s) ?			*/
165/*     s->strstart - (IPos)MAX_DIST(s) : NIL;				*/
166
167		movl	dsWSize(%edx), %eax
168		subl	$MIN_LOOKAHEAD, %eax
169		subl	%eax, %ebp
170		jg	LimitPositive
171		xorl	%ebp, %ebp
172LimitPositive:
173
174/* int best_len = s->prev_length;					*/
175
176		movl	dsPrevLen(%edx), %eax
177		movl	%eax, bestlen(%esp)
178
179/* Store the sum of s->window + best_len in %esi locally, and in %esi.	*/
180
181		addl	%eax, %esi
182		movl	%esi, windowbestlen(%esp)
183
184/* register ush scan_start = *(ushf*)scan;				*/
185/* register ush scan_end   = *(ushf*)(scan+best_len-1);			*/
186/* Posf *prev = s->prev;						*/
187
188		movzwl	(%edi), %ebx
189		movl	%ebx, scanstart(%esp)
190		movzwl	-1(%edi,%eax), %ebx
191		movl	%ebx, scanend(%esp)
192		movl	dsPrev(%edx), %edi
193
194/* Jump into the main loop.						*/
195
196		movl	chainlenwmask(%esp), %edx
197		jmp	LoopEntry
198
199.balign 16
200
201/* do {
202 *     match = s->window + cur_match;
203 *     if (*(ushf*)(match+best_len-1) != scan_end ||
204 *         *(ushf*)match != scan_start) continue;
205 *     [...]
206 * } while ((cur_match = prev[cur_match & wmask]) > limit
207 *          && --chain_length != 0);
208 *
209 * Here is the inner loop of the function. The function will spend the
210 * majority of its time in this loop, and majority of that time will
211 * be spent in the first ten instructions.
212 *
213 * Within this loop:
214 * %ebx = scanend
215 * %ecx = curmatch
216 * %edx = chainlenwmask - i.e., ((chainlen << 16) | wmask)
217 * %esi = windowbestlen - i.e., (window + bestlen)
218 * %edi = prev
219 * %ebp = limit
220 */
221LookupLoop:
222		andl	%edx, %ecx
223		movzwl	(%edi,%ecx,2), %ecx
224		cmpl	%ebp, %ecx
225		jbe	LeaveNow
226		subl	$0x00010000, %edx
227		js	LeaveNow
228LoopEntry:	movzwl	-1(%esi,%ecx), %eax
229		cmpl	%ebx, %eax
230		jnz	LookupLoop
231		movl	window(%esp), %eax
232		movzwl	(%eax,%ecx), %eax
233		cmpl	scanstart(%esp), %eax
234		jnz	LookupLoop
235
236/* Store the current value of chainlen.					*/
237
238		movl	%edx, chainlenwmask(%esp)
239
240/* Point %edi to the string under scrutiny, and %esi to the string we	*/
241/* are hoping to match it up with. In actuality, %esi and %edi are	*/
242/* both pointed (MAX_MATCH_8 - scanalign) bytes ahead, and %edx is	*/
243/* initialized to -(MAX_MATCH_8 - scanalign).				*/
244
245		movl	window(%esp), %esi
246		movl	scan(%esp), %edi
247		addl	%ecx, %esi
248		movl	scanalign(%esp), %eax
249		movl	$(-MAX_MATCH_8), %edx
250		lea	MAX_MATCH_8(%edi,%eax), %edi
251		lea	MAX_MATCH_8(%esi,%eax), %esi
252
253/* Test the strings for equality, 8 bytes at a time. At the end,
254 * adjust %edx so that it is offset to the exact byte that mismatched.
255 *
256 * We already know at this point that the first three bytes of the
257 * strings match each other, and they can be safely passed over before
258 * starting the compare loop. So what this code does is skip over 0-3
259 * bytes, as much as necessary in order to dword-align the %edi
260 * pointer. (%esi will still be misaligned three times out of four.)
261 *
262 * It should be confessed that this loop usually does not represent
263 * much of the total running time. Replacing it with a more
264 * straightforward "rep cmpsb" would not drastically degrade
265 * performance.
266 */
267LoopCmps:
268		movl	(%esi,%edx), %eax
269		xorl	(%edi,%edx), %eax
270		jnz	LeaveLoopCmps
271		movl	4(%esi,%edx), %eax
272		xorl	4(%edi,%edx), %eax
273		jnz	LeaveLoopCmps4
274		addl	$8, %edx
275		jnz	LoopCmps
276		jmp	LenMaximum
277LeaveLoopCmps4:	addl	$4, %edx
278LeaveLoopCmps:	testl	$0x0000FFFF, %eax
279		jnz	LenLower
280		addl	$2, %edx
281		shrl	$16, %eax
282LenLower:	subb	$1, %al
283		adcl	$0, %edx
284
285/* Calculate the length of the match. If it is longer than MAX_MATCH,	*/
286/* then automatically accept it as the best possible match and leave.	*/
287
288		lea	(%edi,%edx), %eax
289		movl	scan(%esp), %edi
290		subl	%edi, %eax
291		cmpl	$MAX_MATCH, %eax
292		jge	LenMaximum
293
294/* If the length of the match is not longer than the best match we	*/
295/* have so far, then forget it and return to the lookup loop.		*/
296
297		movl	deflatestate(%esp), %edx
298		movl	bestlen(%esp), %ebx
299		cmpl	%ebx, %eax
300		jg	LongerMatch
301		movl	windowbestlen(%esp), %esi
302		movl	dsPrev(%edx), %edi
303		movl	scanend(%esp), %ebx
304		movl	chainlenwmask(%esp), %edx
305		jmp	LookupLoop
306
307/*         s->match_start = cur_match;					*/
308/*         best_len = len;						*/
309/*         if (len >= nice_match) break;				*/
310/*         scan_end = *(ushf*)(scan+best_len-1);			*/
311
312LongerMatch:	movl	nicematch(%esp), %ebx
313		movl	%eax, bestlen(%esp)
314		movl	%ecx, dsMatchStart(%edx)
315		cmpl	%ebx, %eax
316		jge	LeaveNow
317		movl	window(%esp), %esi
318		addl	%eax, %esi
319		movl	%esi, windowbestlen(%esp)
320		movzwl	-1(%edi,%eax), %ebx
321		movl	dsPrev(%edx), %edi
322		movl	%ebx, scanend(%esp)
323		movl	chainlenwmask(%esp), %edx
324		jmp	LookupLoop
325
326/* Accept the current string, with the maximum possible length.		*/
327
328LenMaximum:	movl	deflatestate(%esp), %edx
329		movl	$MAX_MATCH, bestlen(%esp)
330		movl	%ecx, dsMatchStart(%edx)
331
332/* if ((uInt)best_len <= s->lookahead) return (uInt)best_len;		*/
333/* return s->lookahead;							*/
334
335LeaveNow:
336		movl	deflatestate(%esp), %edx
337		movl	bestlen(%esp), %ebx
338		movl	dsLookahead(%edx), %eax
339		cmpl	%eax, %ebx
340		jg	LookaheadRet
341		movl	%ebx, %eax
342LookaheadRet:
343
344/* Restore the stack and return from whence we came.			*/
345
346		addl	$LocalVarsSize, %esp
347		.cfi_def_cfa_offset 20
348		popl	%ebx
349		.cfi_def_cfa_offset 16
350		popl	%esi
351		.cfi_def_cfa_offset 12
352		popl	%edi
353		.cfi_def_cfa_offset 8
354		popl	%ebp
355		.cfi_def_cfa_offset 4
356.cfi_endproc
357match_init:	ret