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
88 longest_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
127 LastMatchGood:
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
146 LookaheadLess: 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
172 LimitPositive:
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 */
221 LookupLoop:
222 andl %edx, %ecx
223 movzwl (%edi,%ecx,2), %ecx
224 cmpl %ebp, %ecx
225 jbe LeaveNow
226 subl $0x00010000, %edx
227 js LeaveNow
228 LoopEntry: 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 */
267 LoopCmps:
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
277 LeaveLoopCmps4: addl $4, %edx
278 LeaveLoopCmps: testl $0x0000FFFF, %eax
279 jnz LenLower
280 addl $2, %edx
281 shrl $16, %eax
282 LenLower: 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
312 LongerMatch: 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
328 LenMaximum: 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
335 LeaveNow:
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
342 LookaheadRet:
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
357 match_init: ret