benchtests/bench-strstr.c

   1 /* Measure strstr functions.
   2    Copyright (C) 2013-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #define MIN_PAGE_SIZE 131072
  20 #define TEST_MAIN
  21 #define TEST_NAME "strstr"
  22 #include "bench-string.h"
  23
  24 #include "json-lib.h"
  25
  26 static const char input[] =
  27 "This manual is written with the assumption that you are at least "
  28 "somewhat familiar with the C programming language and basic programming "
  29 "concepts.  Specifically, familiarity with ISO standard C (*note ISO "
  30 "C::), rather than “traditional” pre-ISO C dialects, is assumed.\n"
  31
  32 "   The GNU C Library includes several “header files”, each of which "
  33 "provides definitions and declarations for a group of related facilities; "
  34 "this information is used by the C compiler when processing your program. "
  35 "For example, the header file ‘stdio.h’ declares facilities for "
  36 "performing input and output, and the header file ‘string.h’ declares "
  37 "string processing utilities.  The organization of this manual generally "
  38 "follows the same division as the header files.\n"
  39
  40 "   If you are reading this manual for the first time, you should read "
  41 "all of the introductory material and skim the remaining chapters.  There "
  42 "are a _lot_ of functions in the GNU C Library and it’s not realistic to "
  43 "expect that you will be able to remember exactly _how_ to use each and "
  44 "every one of them.  It’s more important to become generally familiar "
  45 "with the kinds of facilities that the library provides, so that when you "
  46 "are writing your programs you can recognize _when_ to make use of "
  47 "library functions, and _where_ in this manual you can find more specific "
  48 "information about them.\n";
  49
  50 /* Simple yet efficient strstr - for needles < 32 bytes it is 2-4 times
  51    faster than the optimized twoway_strstr.  */
  52 static char *
  53 basic_strstr (const char *s1, const char *s2)
  54 {
  55   size_t i;
  56   int c = s2[0];
  57
  58   if (c == 0)
  59     return (char*)s1;
  60
  61   for ( ; s1[0] != '\0'; s1++)
  62     {
  63       if (s1[0] != c)
  64         continue;
  65       for (i = 1; s2[i] != 0; i++)
  66         if (s1[i] != s2[i])
  67           break;
  68       if (s2[i] == '\0')
  69         return (char*)s1;
  70     }
  71
  72   return NULL;
  73 }
  74
  75 #define RETURN_TYPE char *
  76 #define AVAILABLE(h, h_l, j, n_l)                       \
  77   (((j) + (n_l) <= (h_l)) \
  78    || ((h_l) += __strnlen ((void*)((h) + (h_l)), (n_l) + 512), \
  79        (j) + (n_l) <= (h_l)))
  80 #define CHECK_EOL (1)
  81 #define RET0_IF_0(a) if (!a) goto ret0
  82 #define FASTSEARCH(S,C,N) (void*) strchr ((void*)(S), (C))
  83 #define LONG_NEEDLE_THRESHOLD 32U
  84 #define __strnlen strnlen
  85 #include "string/str-two-way.h"
  86
  87 /* Optimized Two-way implementation from GLIBC 2.29.  */
  88 static char *
  89 twoway_strstr (const char *haystack, const char *needle)
  90 {
  91   size_t needle_len; /* Length of NEEDLE.  */
  92   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  93
  94   /* Handle empty NEEDLE special case.  */
  95   if (needle[0] == '\0')
  96     return (char *) haystack;
  97
  98   /* Skip until we find the first matching char from NEEDLE.  */
  99   haystack = strchr (haystack, needle[0]);
 100   if (haystack == NULL || needle[1] == '\0')
 101     return (char *) haystack;
 102
 103   /* Ensure HAYSTACK length is at least as long as NEEDLE length.
 104      Since a match may occur early on in a huge HAYSTACK, use strnlen
 105      and read ahead a few cachelines for improved performance.  */
 106   needle_len = strlen (needle);
 107   haystack_len = __strnlen (haystack, needle_len + 256);
 108   if (haystack_len < needle_len)
 109     return NULL;
 110
 111   /* Check whether we have a match.  This improves performance since we avoid
 112      the initialization overhead of the two-way algorithm.  */
 113   if (memcmp (haystack, needle, needle_len) == 0)
 114     return (char *) haystack;
 115
 116   /* Perform the search.  Abstract memory is considered to be an array
 117      of 'unsigned char' values, not an array of 'char' values.  See
 118      ISO C 99 section 6.2.6.1.  */
 119   if (needle_len < LONG_NEEDLE_THRESHOLD)
 120     return two_way_short_needle ((const unsigned char *) haystack,
 121                                   haystack_len,
 122                                  (const unsigned char *) needle, needle_len);
 123   return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
 124                               (const unsigned char *) needle, needle_len);
 125 }
 126
 127 typedef char *(*proto_t) (const char *, const char *);
 128
 129 IMPL (strstr, 1)
 130 IMPL (twoway_strstr, 0)
 131 IMPL (basic_strstr, 0)
 132
 133 static void
 134 do_one_test (json_ctx_t *json_ctx, impl_t *impl, const char *s1,
 135              const char *s2, char *exp_result)
 136 {
 137   size_t i, iters = INNER_LOOP_ITERS_SMALL / 8;
 138   timing_t start, stop, cur;
 139   char *res;
 140
 141   TIMING_NOW (start);
 142   for (i = 0; i < iters; ++i)
 143     res = CALL (impl, s1, s2);
 144   TIMING_NOW (stop);
 145
 146   TIMING_DIFF (cur, start, stop);
 147
 148   json_element_double (json_ctx, (double) cur / (double) iters);
 149
 150   if (res != exp_result)
 151     {
 152       error (0, 0, "Wrong result in function %s %s %s", impl->name,
 153              (res == NULL) ? "(null)" : res,
 154              (exp_result == NULL) ? "(null)" : exp_result);
 155       ret = 1;
 156     }
 157 }
 158
 159 static void
 160 do_test (json_ctx_t *json_ctx, size_t align1, size_t align2, size_t len1,
 161          size_t len2, int fail)
 162 {
 163   char *s1 = (char *) (buf1 + align1);
 164   char *s2 = (char *) (buf2 + align2);
 165
 166   size_t size = sizeof (input) - 1;
 167   size_t pos = (len1 + len2) % size;
 168
 169   char *ss2 = s2;
 170   for (size_t l = len2; l > 0; l = l > size ? l - size : 0)
 171     {
 172       size_t t = l > size ? size : l;
 173       if (pos + t <= size)
 174         ss2 = mempcpy (ss2, input + pos, t);
 175       else
 176         {
 177           ss2 = mempcpy (ss2, input + pos, size - pos);
 178           ss2 = mempcpy (ss2, input, t - (size - pos));
 179         }
 180     }
 181   s2[len2] = '\0';
 182
 183   char *ss1 = s1;
 184   for (size_t l = len1; l > 0; l = l > size ? l - size : 0)
 185     {
 186       size_t t = l > size ? size : l;
 187       memcpy (ss1, input, t);
 188       ss1 += t;
 189     }
 190
 191   if (!fail)
 192     memcpy (s1 + len1 - len2, s2, len2);
 193   s1[len1] = '\0';
 194
 195   /* Remove any accidental matches except for the last if !fail.  */
 196   for (ss1 = basic_strstr (s1, s2); ss1; ss1 = basic_strstr (ss1 + 1, s2))
 197     if (fail || ss1 != s1 + len1 - len2)
 198       ++ss1[len2 / 2];
 199
 200   json_element_object_begin (json_ctx);
 201   json_attr_uint (json_ctx, "len_haystack", len1);
 202   json_attr_uint (json_ctx, "len_needle", len2);
 203   json_attr_uint (json_ctx, "align_haystack", align1);
 204   json_attr_uint (json_ctx, "align_needle", align2);
 205   json_attr_uint (json_ctx, "fail", fail);
 206
 207   json_array_begin (json_ctx, "timings");
 208
 209   FOR_EACH_IMPL (impl, 0)
 210     do_one_test (json_ctx, impl, s1, s2, fail ? NULL : s1 + len1 - len2);
 211
 212   json_array_end (json_ctx);
 213   json_element_object_end (json_ctx);
 214
 215 }
 216
 217 /* Test needles which exhibit worst-case performance.  This shows that
 218    basic_strstr is quadratic and thus unsuitable for large needles.
 219    On the other hand Two-way and skip table implementations are linear with
 220    increasing needle sizes.  The slowest cases of the two implementations are
 221    within a factor of 2 on several different microarchitectures.  */
 222
 223 static void
 224 test_hard_needle (json_ctx_t *json_ctx, size_t ne_len, size_t hs_len)
 225 {
 226   char *ne = (char *) buf1;
 227   char *hs = (char *) buf2;
 228
 229   /* Hard needle for strstr algorithm using skip table.  This results in many
 230      memcmp calls comparing most of the needle.  */
 231   {
 232     memset (ne, 'a', ne_len);
 233     ne[ne_len] = '\0';
 234     ne[ne_len - 14] = 'b';
 235
 236     memset (hs, 'a', hs_len);
 237     for (size_t i = ne_len; i <= hs_len; i += ne_len)
 238       {
 239         hs[i - 5] = 'b';
 240         hs[i - 62] = 'b';
 241       }
 242
 243     json_element_object_begin (json_ctx);
 244     json_attr_uint (json_ctx, "len_haystack", hs_len);
 245     json_attr_uint (json_ctx, "len_needle", ne_len);
 246     json_attr_uint (json_ctx, "align_haystack", 0);
 247     json_attr_uint (json_ctx, "align_needle", 0);
 248     json_attr_uint (json_ctx, "fail", 1);
 249     json_attr_string (json_ctx, "desc", "Difficult skiptable(0)");
 250
 251     json_array_begin (json_ctx, "timings");
 252
 253     FOR_EACH_IMPL (impl, 0)
 254       do_one_test (json_ctx, impl, hs, ne, NULL);
 255
 256     json_array_end (json_ctx);
 257     json_element_object_end (json_ctx);
 258   }
 259
 260   /* 2nd hard needle for strstr algorithm using skip table.  This results in
 261      many memcmp calls comparing most of the needle.  */
 262   {
 263     memset (ne, 'a', ne_len);
 264     ne[ne_len] = '\0';
 265     ne[ne_len - 6] = 'b';
 266
 267     memset (hs, 'a', hs_len);
 268     for (size_t i = ne_len; i <= hs_len; i += ne_len)
 269       {
 270         hs[i - 5] = 'b';
 271         hs[i - 6] = 'b';
 272       }
 273
 274     json_element_object_begin (json_ctx);
 275     json_attr_uint (json_ctx, "len_haystack", hs_len);
 276     json_attr_uint (json_ctx, "len_needle", ne_len);
 277     json_attr_uint (json_ctx, "align_haystack", 0);
 278     json_attr_uint (json_ctx, "align_needle", 0);
 279     json_attr_uint (json_ctx, "fail", 1);
 280     json_attr_string (json_ctx, "desc", "Difficult skiptable(1)");
 281
 282     json_array_begin (json_ctx, "timings");
 283
 284     FOR_EACH_IMPL (impl, 0)
 285       do_one_test (json_ctx, impl, hs, ne, NULL);
 286
 287     json_array_end (json_ctx);
 288     json_element_object_end (json_ctx);
 289   }
 290
 291   /* Hard needle for Two-way algorithm - the random input causes a large number
 292      of branch mispredictions which significantly reduces performance on modern
 293      micro architectures.  */
 294   {
 295     for (int i = 0; i < hs_len; i++)
 296       hs[i] = (rand () & 255) > 155 ? 'a' : 'b';
 297     hs[hs_len] = 0;
 298
 299     memset (ne, 'a', ne_len);
 300     ne[ne_len - 2] = 'b';
 301     ne[0] = 'b';
 302     ne[ne_len] = 0;
 303
 304     json_element_object_begin (json_ctx);
 305     json_attr_uint (json_ctx, "len_haystack", hs_len);
 306     json_attr_uint (json_ctx, "len_needle", ne_len);
 307     json_attr_uint (json_ctx, "align_haystack", 0);
 308     json_attr_uint (json_ctx, "align_needle", 0);
 309     json_attr_uint (json_ctx, "fail", 1);
 310     json_attr_string (json_ctx, "desc", "Difficult 2-way");
 311
 312     json_array_begin (json_ctx, "timings");
 313
 314     FOR_EACH_IMPL (impl, 0)
 315       do_one_test (json_ctx, impl, hs, ne, NULL);
 316
 317     json_array_end (json_ctx);
 318     json_element_object_end (json_ctx);
 319   }
 320
 321   /* Hard needle for standard algorithm testing first few characters of
 322    * needle.  */
 323   {
 324     for (int i = 0; i < hs_len; i++)
 325       hs[i] = (rand () & 255) >= 128 ? 'a' : 'b';
 326     hs[hs_len] = 0;
 327
 328     for (int i = 0; i < ne_len; i++)
 329       {
 330         if (i % 3 == 0)
 331           ne[i] = 'a';
 332         else if (i % 3 == 1)
 333           ne[i] = 'b';
 334         else
 335           ne[i] = 'c';
 336       }
 337     ne[ne_len] = 0;
 338
 339     json_element_object_begin (json_ctx);
 340     json_attr_uint (json_ctx, "len_haystack", hs_len);
 341     json_attr_uint (json_ctx, "len_needle", ne_len);
 342     json_attr_uint (json_ctx, "align_haystack", 0);
 343     json_attr_uint (json_ctx, "align_needle", 0);
 344     json_attr_uint (json_ctx, "fail", 1);
 345     json_attr_string (json_ctx, "desc", "Difficult testing first 2");
 346
 347     json_array_begin (json_ctx, "timings");
 348
 349     FOR_EACH_IMPL (impl, 0)
 350       do_one_test (json_ctx, impl, hs, ne, NULL);
 351
 352     json_array_end (json_ctx);
 353     json_element_object_end (json_ctx);
 354   }
 355 }
 356
 357 static int
 358 test_main (void)
 359 {
 360   json_ctx_t json_ctx;
 361   test_init ();
 362
 363   json_init (&json_ctx, 0, stdout);
 364
 365   json_document_begin (&json_ctx);
 366   json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
 367
 368   json_attr_object_begin (&json_ctx, "functions");
 369   json_attr_object_begin (&json_ctx, TEST_NAME);
 370   json_attr_string (&json_ctx, "bench-variant", "");
 371
 372   json_array_begin (&json_ctx, "ifuncs");
 373   FOR_EACH_IMPL (impl, 0)
 374     json_element_string (&json_ctx, impl->name);
 375   json_array_end (&json_ctx);
 376
 377   json_array_begin (&json_ctx, "results");
 378
 379   for (size_t hlen = 8; hlen <= 256;)
 380     for (size_t klen = 1; klen <= 16; klen++)
 381       {
 382         do_test (&json_ctx, 1, 3, hlen, klen, 0);
 383         do_test (&json_ctx, 0, 9, hlen, klen, 1);
 384
 385         do_test (&json_ctx, 1, 3, hlen + 1, klen, 0);
 386         do_test (&json_ctx, 0, 9, hlen + 1, klen, 1);
 387
 388         do_test (&json_ctx, getpagesize () - 15, 9, hlen, klen, 1);
 389         if (hlen < 64)
 390           {
 391             hlen += 8;
 392           }
 393         else
 394           {
 395             hlen += 32;
 396           }
 397       }
 398
 399   for (size_t hlen = 256; hlen <= 65536; hlen *= 2)
 400     for (size_t klen = 4; klen <= 256; klen *= 2)
 401       {
 402         do_test (&json_ctx, 1, 11, hlen, klen, 0);
 403         do_test (&json_ctx, 14, 5, hlen, klen, 1);
 404
 405     do_test (&json_ctx, 1, 11, hlen + 1, klen + 1, 0);
 406     do_test (&json_ctx, 14, 5, hlen + 1, klen + 1, 1);
 407
 408         do_test (&json_ctx, 1, 11, hlen + 1, klen, 0);
 409         do_test (&json_ctx, 14, 5, hlen + 1, klen, 1);
 410
 411         do_test (&json_ctx, getpagesize () - 15, 5, hlen + 1, klen, 1);
 412       }
 413
 414   test_hard_needle (&json_ctx, 64, 65536);
 415   test_hard_needle (&json_ctx, 256, 65536);
 416   test_hard_needle (&json_ctx, 1024, 65536);
 417
 418   json_array_end (&json_ctx);
 419   json_attr_object_end (&json_ctx);
 420   json_attr_object_end (&json_ctx);
 421   json_document_end (&json_ctx);
 422
 423   return ret;
 424 }
 425
 426 #include <support/test-driver.c>