reactos/dll/zlib/contrib/asm586/match.S

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