gdb/gnulib/memcmp.c

   1 /* Copyright (C) 1991, 1993, 1995, 1997, 1998, 2003, 2006, 2009
   2 Free Software Foundation, Inc.
   3
   4    Contributed by Torbjorn Granlund (tege@sics.se).
   5
   6    NOTE: The canonical source of this file is maintained with the GNU C Library.
   7    Bugs can be reported to bug-glibc@prep.ai.mit.edu.
   8
   9    This program is free software: you can redistribute it and/or modify it
  10    under the terms of the GNU General Public License as published by the
  11    Free Software Foundation; either version 3 of the License, or any
  12    later version.
  13
  14    This program is distributed in the hope that it will be useful,
  15    but WITHOUT ANY WARRANTY; without even the implied warranty of
  16    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17    GNU General Public License for more details.
  18
  19    You should have received a copy of the GNU General Public License
  20    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  21
  22 #ifndef _LIBC
  23 # include <config.h>
  24 #endif
  25
  26 #include <string.h>
  27
  28 #undef memcmp
  29
  30 #ifdef _LIBC
  31
  32 # include <memcopy.h>
  33 # include <endian.h>
  34
  35 # if __BYTE_ORDER == __BIG_ENDIAN
  36 #  define WORDS_BIGENDIAN
  37 # endif
  38
  39 #else   /* Not in the GNU C library.  */
  40
  41 # include <sys/types.h>
  42
  43 /* Type to use for aligned memory operations.
  44    This should normally be the biggest type supported by a single load
  45    and store.  Must be an unsigned type.  */
  46 # define op_t   unsigned long int
  47 # define OPSIZ  (sizeof(op_t))
  48
  49 /* Threshold value for when to enter the unrolled loops.  */
  50 # define OP_T_THRES     16
  51
  52 /* Type to use for unaligned operations.  */
  53 typedef unsigned char byte;
  54
  55 # ifndef WORDS_BIGENDIAN
  56 #  define MERGE(w0, sh_1, w1, sh_2) (((w0) >> (sh_1)) | ((w1) << (sh_2)))
  57 # else
  58 #  define MERGE(w0, sh_1, w1, sh_2) (((w0) << (sh_1)) | ((w1) >> (sh_2)))
  59 # endif
  60
  61 #endif  /* In the GNU C library.  */
  62
  63 #ifdef WORDS_BIGENDIAN
  64 # define CMP_LT_OR_GT(a, b) ((a) > (b) ? 1 : -1)
  65 #else
  66 # define CMP_LT_OR_GT(a, b) memcmp_bytes ((a), (b))
  67 #endif
  68
  69 /* BE VERY CAREFUL IF YOU CHANGE THIS CODE!  */
  70
  71 /* The strategy of this memcmp is:
  72
  73    1. Compare bytes until one of the block pointers is aligned.
  74
  75    2. Compare using memcmp_common_alignment or
  76       memcmp_not_common_alignment, regarding the alignment of the other
  77       block after the initial byte operations.  The maximum number of
  78       full words (of type op_t) are compared in this way.
  79
  80    3. Compare the few remaining bytes.  */
  81
  82 #ifndef WORDS_BIGENDIAN
  83 /* memcmp_bytes -- Compare A and B bytewise in the byte order of the machine.
  84    A and B are known to be different.
  85    This is needed only on little-endian machines.  */
  86
  87 # ifdef  __GNUC__
  88 __inline
  89 # endif
  90 static int
  91 memcmp_bytes (long unsigned int a, long unsigned int b)
  92 {
  93   long int srcp1 = (long int) &a;
  94   long int srcp2 = (long int) &b;
  95   op_t a0, b0;
  96
  97   do
  98     {
  99       a0 = ((byte *) srcp1)[0];
 100       b0 = ((byte *) srcp2)[0];
 101       srcp1 += 1;
 102       srcp2 += 1;
 103     }
 104   while (a0 == b0);
 105   return a0 - b0;
 106 }
 107 #endif
 108
 109 /* memcmp_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN `op_t'
 110    objects (not LEN bytes!).  Both SRCP1 and SRCP2 should be aligned for
 111    memory operations on `op_t's.  */
 112 #ifdef  __GNUC__
 113 __inline
 114 #endif
 115 static int
 116 memcmp_common_alignment (long int srcp1, long int srcp2, size_t len)
 117 {
 118   op_t a0, a1;
 119   op_t b0, b1;
 120
 121   switch (len % 4)
 122     {
 123     default: /* Avoid warning about uninitialized local variables.  */
 124     case 2:
 125       a0 = ((op_t *) srcp1)[0];
 126       b0 = ((op_t *) srcp2)[0];
 127       srcp1 -= 2 * OPSIZ;
 128       srcp2 -= 2 * OPSIZ;
 129       len += 2;
 130       goto do1;
 131     case 3:
 132       a1 = ((op_t *) srcp1)[0];
 133       b1 = ((op_t *) srcp2)[0];
 134       srcp1 -= OPSIZ;
 135       srcp2 -= OPSIZ;
 136       len += 1;
 137       goto do2;
 138     case 0:
 139       if (OP_T_THRES <= 3 * OPSIZ && len == 0)
 140         return 0;
 141       a0 = ((op_t *) srcp1)[0];
 142       b0 = ((op_t *) srcp2)[0];
 143       goto do3;
 144     case 1:
 145       a1 = ((op_t *) srcp1)[0];
 146       b1 = ((op_t *) srcp2)[0];
 147       srcp1 += OPSIZ;
 148       srcp2 += OPSIZ;
 149       len -= 1;
 150       if (OP_T_THRES <= 3 * OPSIZ && len == 0)
 151         goto do0;
 152       /* Fall through.  */
 153     }
 154
 155   do
 156     {
 157       a0 = ((op_t *) srcp1)[0];
 158       b0 = ((op_t *) srcp2)[0];
 159       if (a1 != b1)
 160         return CMP_LT_OR_GT (a1, b1);
 161
 162     do3:
 163       a1 = ((op_t *) srcp1)[1];
 164       b1 = ((op_t *) srcp2)[1];
 165       if (a0 != b0)
 166         return CMP_LT_OR_GT (a0, b0);
 167
 168     do2:
 169       a0 = ((op_t *) srcp1)[2];
 170       b0 = ((op_t *) srcp2)[2];
 171       if (a1 != b1)
 172         return CMP_LT_OR_GT (a1, b1);
 173
 174     do1:
 175       a1 = ((op_t *) srcp1)[3];
 176       b1 = ((op_t *) srcp2)[3];
 177       if (a0 != b0)
 178         return CMP_LT_OR_GT (a0, b0);
 179
 180       srcp1 += 4 * OPSIZ;
 181       srcp2 += 4 * OPSIZ;
 182       len -= 4;
 183     }
 184   while (len != 0);
 185
 186   /* This is the right position for do0.  Please don't move
 187      it into the loop.  */
 188  do0:
 189   if (a1 != b1)
 190     return CMP_LT_OR_GT (a1, b1);
 191   return 0;
 192 }
 193
 194 /* memcmp_not_common_alignment -- Compare blocks at SRCP1 and SRCP2 with LEN
 195    `op_t' objects (not LEN bytes!).  SRCP2 should be aligned for memory
 196    operations on `op_t', but SRCP1 *should be unaligned*.  */
 197 #ifdef  __GNUC__
 198 __inline
 199 #endif
 200 static int
 201 memcmp_not_common_alignment (long int srcp1, long int srcp2, size_t len)
 202 {
 203   op_t a0, a1, a2, a3;
 204   op_t b0, b1, b2, b3;
 205   op_t x;
 206   int shl, shr;
 207
 208   /* Calculate how to shift a word read at the memory operation
 209      aligned srcp1 to make it aligned for comparison.  */
 210
 211   shl = 8 * (srcp1 % OPSIZ);
 212   shr = 8 * OPSIZ - shl;
 213
 214   /* Make SRCP1 aligned by rounding it down to the beginning of the `op_t'
 215      it points in the middle of.  */
 216   srcp1 &= -OPSIZ;
 217
 218   switch (len % 4)
 219     {
 220     default: /* Avoid warning about uninitialized local variables.  */
 221     case 2:
 222       a1 = ((op_t *) srcp1)[0];
 223       a2 = ((op_t *) srcp1)[1];
 224       b2 = ((op_t *) srcp2)[0];
 225       srcp1 -= 1 * OPSIZ;
 226       srcp2 -= 2 * OPSIZ;
 227       len += 2;
 228       goto do1;
 229     case 3:
 230       a0 = ((op_t *) srcp1)[0];
 231       a1 = ((op_t *) srcp1)[1];
 232       b1 = ((op_t *) srcp2)[0];
 233       srcp2 -= 1 * OPSIZ;
 234       len += 1;
 235       goto do2;
 236     case 0:
 237       if (OP_T_THRES <= 3 * OPSIZ && len == 0)
 238         return 0;
 239       a3 = ((op_t *) srcp1)[0];
 240       a0 = ((op_t *) srcp1)[1];
 241       b0 = ((op_t *) srcp2)[0];
 242       srcp1 += 1 * OPSIZ;
 243       goto do3;
 244     case 1:
 245       a2 = ((op_t *) srcp1)[0];
 246       a3 = ((op_t *) srcp1)[1];
 247       b3 = ((op_t *) srcp2)[0];
 248       srcp1 += 2 * OPSIZ;
 249       srcp2 += 1 * OPSIZ;
 250       len -= 1;
 251       if (OP_T_THRES <= 3 * OPSIZ && len == 0)
 252         goto do0;
 253       /* Fall through.  */
 254     }
 255
 256   do
 257     {
 258       a0 = ((op_t *) srcp1)[0];
 259       b0 = ((op_t *) srcp2)[0];
 260       x = MERGE(a2, shl, a3, shr);
 261       if (x != b3)
 262         return CMP_LT_OR_GT (x, b3);
 263
 264     do3:
 265       a1 = ((op_t *) srcp1)[1];
 266       b1 = ((op_t *) srcp2)[1];
 267       x = MERGE(a3, shl, a0, shr);
 268       if (x != b0)
 269         return CMP_LT_OR_GT (x, b0);
 270
 271     do2:
 272       a2 = ((op_t *) srcp1)[2];
 273       b2 = ((op_t *) srcp2)[2];
 274       x = MERGE(a0, shl, a1, shr);
 275       if (x != b1)
 276         return CMP_LT_OR_GT (x, b1);
 277
 278     do1:
 279       a3 = ((op_t *) srcp1)[3];
 280       b3 = ((op_t *) srcp2)[3];
 281       x = MERGE(a1, shl, a2, shr);
 282       if (x != b2)
 283         return CMP_LT_OR_GT (x, b2);
 284
 285       srcp1 += 4 * OPSIZ;
 286       srcp2 += 4 * OPSIZ;
 287       len -= 4;
 288     }
 289   while (len != 0);
 290
 291   /* This is the right position for do0.  Please don't move
 292      it into the loop.  */
 293  do0:
 294   x = MERGE(a2, shl, a3, shr);
 295   if (x != b3)
 296     return CMP_LT_OR_GT (x, b3);
 297   return 0;
 298 }
 299
 300 int
 301 rpl_memcmp (const void *s1, const void *s2, size_t len)
 302 {
 303   op_t a0;
 304   op_t b0;
 305   long int srcp1 = (long int) s1;
 306   long int srcp2 = (long int) s2;
 307   op_t res;
 308
 309   if (len >= OP_T_THRES)
 310     {
 311       /* There are at least some bytes to compare.  No need to test
 312          for LEN == 0 in this alignment loop.  */
 313       while (srcp2 % OPSIZ != 0)
 314         {
 315           a0 = ((byte *) srcp1)[0];
 316           b0 = ((byte *) srcp2)[0];
 317           srcp1 += 1;
 318           srcp2 += 1;
 319           res = a0 - b0;
 320           if (res != 0)
 321             return res;
 322           len -= 1;
 323         }
 324
 325       /* SRCP2 is now aligned for memory operations on `op_t'.
 326          SRCP1 alignment determines if we can do a simple,
 327          aligned compare or need to shuffle bits.  */
 328
 329       if (srcp1 % OPSIZ == 0)
 330         res = memcmp_common_alignment (srcp1, srcp2, len / OPSIZ);
 331       else
 332         res = memcmp_not_common_alignment (srcp1, srcp2, len / OPSIZ);
 333       if (res != 0)
 334         return res;
 335
 336       /* Number of bytes remaining in the interval [0..OPSIZ-1].  */
 337       srcp1 += len & -OPSIZ;
 338       srcp2 += len & -OPSIZ;
 339       len %= OPSIZ;
 340     }
 341
 342   /* There are just a few bytes to compare.  Use byte memory operations.  */
 343   while (len != 0)
 344     {
 345       a0 = ((byte *) srcp1)[0];
 346       b0 = ((byte *) srcp2)[0];
 347       srcp1 += 1;
 348       srcp2 += 1;
 349       res = a0 - b0;
 350       if (res != 0)
 351         return res;
 352       len -= 1;
 353     }
 354
 355   return 0;
 356 }
 357
 358 #ifdef weak_alias
 359 # undef bcmp
 360 weak_alias (memcmp, bcmp)
 361 #endif