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 (at) 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 358
