root/lib/zlib/contrib/asm686/match.S

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   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 
  73 longest_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
 105 LastMatchGood:
 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
 124 LookaheadLess:  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
 150 LimitPositive:
 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  */
 199 LookupLoop:
 200                 andl    %edx, %ecx
 201                 movzwl  (%edi,%ecx,2), %ecx
 202                 cmpl    %ebp, %ecx
 203                 jbe     LeaveNow
 204                 subl    $0x00010000, %edx
 205                 js      LeaveNow
 206 LoopEntry:      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  */
 245 LoopCmps:
 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
 255 LeaveLoopCmps4: addl    $4, %edx
 256 LeaveLoopCmps:  testl   $0x0000FFFF, %eax
 257                 jnz     LenLower
 258                 addl    $2, %edx
 259                 shrl    $16, %eax
 260 LenLower:       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 
 290 LongerMatch:    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 
 306 LenMaximum:     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 
 313 LeaveNow:
 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
 320 LookaheadRet:
 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
 329 match_init:     ret

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