root/lib/zlib/contrib/asm586/match.S

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   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 
  81 longest_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
 107 LookaheadLess:  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
 133 LimitPositive:
 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
 146 LastMatchGood:
 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  */
 224 LookupLoop:
 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 */
 232 LoopEntry:      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  */
 275 LoopCmps:
 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
 287 LeaveLoopCmps4: addl    $4, %edx
 288 LeaveLoopCmps:  testl   $0x0000FFFF, %eax
 289                 jnz     LenLower
 290                 addl    $2, %edx
 291                 shrl    $16, %eax
 292 LenLower:       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 
 323 LongerMatch:    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 
 341 LenMaximum:     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 
 348 LeaveNow:
 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
 355 LookaheadRet:
 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
 364 match_init:     ret

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