source: trunk/minix/lib/zlib-1.2.3/contrib/asm586/match.S@ 16

Last change on this file since 16 was 9, checked in by Mattia Monga, 14 years ago

Minix 3.1.2a
File size: 10.6 KB
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[9]1/* match.s -- Pentium-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 wmask 0 /* local copy of s->wmask */
22#define window 4 /* local copy of s->window */
23#define windowbestlen 8 /* s->window + bestlen */
24#define chainlenscanend 12 /* high word: current chain len */
25 /* low word: last bytes sought */
26#define scanstart 16 /* first 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/* Offsets for fields in the deflate_state structure. These numbers
42 * are calculated from the definition of deflate_state, with the
43 * assumption that the compiler will dword-align the fields. (Thus,
44 * changing the definition of deflate_state could easily cause this
45 * program to crash horribly, without so much as a warning at
46 * compile time. Sigh.)
47 */
48
49/* All the +zlib1222add offsets are due to the addition of fields
50 * in zlib in the deflate_state structure since the asm code was first written
51 * (if you compile with zlib 1.0.4 or older, use "zlib1222add equ (-4)").
52 * (if you compile with zlib between 1.0.5 and 1.2.2.1, use "zlib1222add equ 0").
53 * if you compile with zlib 1.2.2.2 or later , use "zlib1222add equ 8").
54 */
55
56#define zlib1222add (8)
57
58#define dsWSize (36+zlib1222add)
59#define dsWMask (44+zlib1222add)
60#define dsWindow (48+zlib1222add)
61#define dsPrev (56+zlib1222add)
62#define dsMatchLen (88+zlib1222add)
63#define dsPrevMatch (92+zlib1222add)
64#define dsStrStart (100+zlib1222add)
65#define dsMatchStart (104+zlib1222add)
66#define dsLookahead (108+zlib1222add)
67#define dsPrevLen (112+zlib1222add)
68#define dsMaxChainLen (116+zlib1222add)
69#define dsGoodMatch (132+zlib1222add)
70#define dsNiceMatch (136+zlib1222add)
71
72
73.file "match.S"
74
75.globl match_init, longest_match
76
77.text
78
79/* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */
80
81longest_match:
82
83/* Save registers that the compiler may be using, and adjust %esp to */
84/* make room for our stack frame. */
85
86 pushl %ebp
87 pushl %edi
88 pushl %esi
89 pushl %ebx
90 subl $LocalVarsSize, %esp
91
92/* Retrieve the function arguments. %ecx will hold cur_match */
93/* throughout the entire function. %edx will hold the pointer to the */
94/* deflate_state structure during the function's setup (before */
95/* entering the main loop). */
96
97 movl deflatestate(%esp), %edx
98 movl curmatch(%esp), %ecx
99
100/* if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead; */
101
102 movl dsNiceMatch(%edx), %eax
103 movl dsLookahead(%edx), %ebx
104 cmpl %eax, %ebx
105 jl LookaheadLess
106 movl %eax, %ebx
107LookaheadLess: movl %ebx, nicematch(%esp)
108
109/* register Bytef *scan = s->window + s->strstart; */
110
111 movl dsWindow(%edx), %esi
112 movl %esi, window(%esp)
113 movl dsStrStart(%edx), %ebp
114 lea (%esi,%ebp), %edi
115 movl %edi, scan(%esp)
116
117/* Determine how many bytes the scan ptr is off from being */
118/* dword-aligned. */
119
120 movl %edi, %eax
121 negl %eax
122 andl $3, %eax
123 movl %eax, scanalign(%esp)
124
125/* IPos limit = s->strstart > (IPos)MAX_DIST(s) ? */
126/* s->strstart - (IPos)MAX_DIST(s) : NIL; */
127
128 movl dsWSize(%edx), %eax
129 subl $MIN_LOOKAHEAD, %eax
130 subl %eax, %ebp
131 jg LimitPositive
132 xorl %ebp, %ebp
133LimitPositive:
134
135/* unsigned chain_length = s->max_chain_length; */
136/* if (s->prev_length >= s->good_match) { */
137/* chain_length >>= 2; */
138/* } */
139
140 movl dsPrevLen(%edx), %eax
141 movl dsGoodMatch(%edx), %ebx
142 cmpl %ebx, %eax
143 movl dsMaxChainLen(%edx), %ebx
144 jl LastMatchGood
145 shrl $2, %ebx
146LastMatchGood:
147
148/* chainlen is decremented once beforehand so that the function can */
149/* use the sign flag instead of the zero flag for the exit test. */
150/* It is then shifted into the high word, to make room for the scanend */
151/* scanend value, which it will always accompany. */
152
153 decl %ebx
154 shll $16, %ebx
155
156/* int best_len = s->prev_length; */
157
158 movl dsPrevLen(%edx), %eax
159 movl %eax, bestlen(%esp)
160
161/* Store the sum of s->window + best_len in %esi locally, and in %esi. */
162
163 addl %eax, %esi
164 movl %esi, windowbestlen(%esp)
165
166/* register ush scan_start = *(ushf*)scan; */
167/* register ush scan_end = *(ushf*)(scan+best_len-1); */
168
169 movw (%edi), %bx
170 movw %bx, scanstart(%esp)
171 movw -1(%edi,%eax), %bx
172 movl %ebx, chainlenscanend(%esp)
173
174/* Posf *prev = s->prev; */
175/* uInt wmask = s->w_mask; */
176
177 movl dsPrev(%edx), %edi
178 movl dsWMask(%edx), %edx
179 mov %edx, wmask(%esp)
180
181/* Jump into the main loop. */
182
183 jmp LoopEntry
184
185.balign 16
186
187/* do {
188 * match = s->window + cur_match;
189 * if (*(ushf*)(match+best_len-1) != scan_end ||
190 * *(ushf*)match != scan_start) continue;
191 * [...]
192 * } while ((cur_match = prev[cur_match & wmask]) > limit
193 * && --chain_length != 0);
194 *
195 * Here is the inner loop of the function. The function will spend the
196 * majority of its time in this loop, and majority of that time will
197 * be spent in the first ten instructions.
198 *
199 * Within this loop:
200 * %ebx = chainlenscanend - i.e., ((chainlen << 16) | scanend)
201 * %ecx = curmatch
202 * %edx = curmatch & wmask
203 * %esi = windowbestlen - i.e., (window + bestlen)
204 * %edi = prev
205 * %ebp = limit
206 *
207 * Two optimization notes on the choice of instructions:
208 *
209 * The first instruction uses a 16-bit address, which costs an extra,
210 * unpairable cycle. This is cheaper than doing a 32-bit access and
211 * zeroing the high word, due to the 3-cycle misalignment penalty which
212 * would occur half the time. This also turns out to be cheaper than
213 * doing two separate 8-bit accesses, as the memory is so rarely in the
214 * L1 cache.
215 *
216 * The window buffer, however, apparently spends a lot of time in the
217 * cache, and so it is faster to retrieve the word at the end of the
218 * match string with two 8-bit loads. The instructions that test the
219 * word at the beginning of the match string, however, are executed
220 * much less frequently, and there it was cheaper to use 16-bit
221 * instructions, which avoided the necessity of saving off and
222 * subsequently reloading one of the other registers.
223 */
224LookupLoop:
225 /* 1 U & V */
226 movw (%edi,%edx,2), %cx /* 2 U pipe */
227 movl wmask(%esp), %edx /* 2 V pipe */
228 cmpl %ebp, %ecx /* 3 U pipe */
229 jbe LeaveNow /* 3 V pipe */
230 subl $0x00010000, %ebx /* 4 U pipe */
231 js LeaveNow /* 4 V pipe */
232LoopEntry: movb -1(%esi,%ecx), %al /* 5 U pipe */
233 andl %ecx, %edx /* 5 V pipe */
234 cmpb %bl, %al /* 6 U pipe */
235 jnz LookupLoop /* 6 V pipe */
236 movb (%esi,%ecx), %ah
237 cmpb %bh, %ah
238 jnz LookupLoop
239 movl window(%esp), %eax
240 movw (%eax,%ecx), %ax
241 cmpw scanstart(%esp), %ax
242 jnz LookupLoop
243
244/* Store the current value of chainlen. */
245
246 movl %ebx, chainlenscanend(%esp)
247
248/* Point %edi to the string under scrutiny, and %esi to the string we */
249/* are hoping to match it up with. In actuality, %esi and %edi are */
250/* both pointed (MAX_MATCH_8 - scanalign) bytes ahead, and %edx is */
251/* initialized to -(MAX_MATCH_8 - scanalign). */
252
253 movl window(%esp), %esi
254 movl scan(%esp), %edi
255 addl %ecx, %esi
256 movl scanalign(%esp), %eax
257 movl $(-MAX_MATCH_8), %edx
258 lea MAX_MATCH_8(%edi,%eax), %edi
259 lea MAX_MATCH_8(%esi,%eax), %esi
260
261/* Test the strings for equality, 8 bytes at a time. At the end,
262 * adjust %edx so that it is offset to the exact byte that mismatched.
263 *
264 * We already know at this point that the first three bytes of the
265 * strings match each other, and they can be safely passed over before
266 * starting the compare loop. So what this code does is skip over 0-3
267 * bytes, as much as necessary in order to dword-align the %edi
268 * pointer. (%esi will still be misaligned three times out of four.)
269 *
270 * It should be confessed that this loop usually does not represent
271 * much of the total running time. Replacing it with a more
272 * straightforward "rep cmpsb" would not drastically degrade
273 * performance.
274 */
275LoopCmps:
276 movl (%esi,%edx), %eax
277 movl (%edi,%edx), %ebx
278 xorl %ebx, %eax
279 jnz LeaveLoopCmps
280 movl 4(%esi,%edx), %eax
281 movl 4(%edi,%edx), %ebx
282 xorl %ebx, %eax
283 jnz LeaveLoopCmps4
284 addl $8, %edx
285 jnz LoopCmps
286 jmp LenMaximum
287LeaveLoopCmps4: addl $4, %edx
288LeaveLoopCmps: testl $0x0000FFFF, %eax
289 jnz LenLower
290 addl $2, %edx
291 shrl $16, %eax
292LenLower: subb $1, %al
293 adcl $0, %edx
294
295/* Calculate the length of the match. If it is longer than MAX_MATCH, */
296/* then automatically accept it as the best possible match and leave. */
297
298 lea (%edi,%edx), %eax
299 movl scan(%esp), %edi
300 subl %edi, %eax
301 cmpl $MAX_MATCH, %eax
302 jge LenMaximum
303
304/* If the length of the match is not longer than the best match we */
305/* have so far, then forget it and return to the lookup loop. */
306
307 movl deflatestate(%esp), %edx
308 movl bestlen(%esp), %ebx
309 cmpl %ebx, %eax
310 jg LongerMatch
311 movl chainlenscanend(%esp), %ebx
312 movl windowbestlen(%esp), %esi
313 movl dsPrev(%edx), %edi
314 movl wmask(%esp), %edx
315 andl %ecx, %edx
316 jmp LookupLoop
317
318/* s->match_start = cur_match; */
319/* best_len = len; */
320/* if (len >= nice_match) break; */
321/* scan_end = *(ushf*)(scan+best_len-1); */
322
323LongerMatch: movl nicematch(%esp), %ebx
324 movl %eax, bestlen(%esp)
325 movl %ecx, dsMatchStart(%edx)
326 cmpl %ebx, %eax
327 jge LeaveNow
328 movl window(%esp), %esi
329 addl %eax, %esi
330 movl %esi, windowbestlen(%esp)
331 movl chainlenscanend(%esp), %ebx
332 movw -1(%edi,%eax), %bx
333 movl dsPrev(%edx), %edi
334 movl %ebx, chainlenscanend(%esp)
335 movl wmask(%esp), %edx
336 andl %ecx, %edx
337 jmp LookupLoop
338
339/* Accept the current string, with the maximum possible length. */
340
341LenMaximum: movl deflatestate(%esp), %edx
342 movl $MAX_MATCH, bestlen(%esp)
343 movl %ecx, dsMatchStart(%edx)
344
345/* if ((uInt)best_len <= s->lookahead) return (uInt)best_len; */
346/* return s->lookahead; */
347
348LeaveNow:
349 movl deflatestate(%esp), %edx
350 movl bestlen(%esp), %ebx
351 movl dsLookahead(%edx), %eax
352 cmpl %eax, %ebx
353 jg LookaheadRet
354 movl %ebx, %eax
355LookaheadRet:
356
357/* Restore the stack and return from whence we came. */
358
359 addl $LocalVarsSize, %esp
360 popl %ebx
361 popl %esi
362 popl %edi
363 popl %ebp
364match_init: ret
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