about summary refs log tree commit diff
path: root/benchtests/bench-strstr.c
blob: 467418b12c4c979f1031a9bc87346ed1be00a3be (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
/* Measure strstr functions.
   Copyright (C) 2013-2022 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#define MIN_PAGE_SIZE 131072
#define TEST_MAIN
#define TEST_NAME "strstr"
#include "bench-string.h"

static const char input[] =
"This manual is written with the assumption that you are at least "
"somewhat familiar with the C programming language and basic programming "
"concepts.  Specifically, familiarity with ISO standard C (*note ISO "
"C::), rather than “traditional” pre-ISO C dialects, is assumed.\n"

"   The GNU C Library includes several “header files”, each of which "
"provides definitions and declarations for a group of related facilities; "
"this information is used by the C compiler when processing your program. "
"For example, the header file ‘stdio.h’ declares facilities for "
"performing input and output, and the header file ‘string.h’ declares "
"string processing utilities.  The organization of this manual generally "
"follows the same division as the header files.\n"

"   If you are reading this manual for the first time, you should read "
"all of the introductory material and skim the remaining chapters.  There "
"are a _lot_ of functions in the GNU C Library and it’s not realistic to "
"expect that you will be able to remember exactly _how_ to use each and "
"every one of them.  It’s more important to become generally familiar "
"with the kinds of facilities that the library provides, so that when you "
"are writing your programs you can recognize _when_ to make use of "
"library functions, and _where_ in this manual you can find more specific "
"information about them.\n";

/* Simple yet efficient strstr - for needles < 32 bytes it is 2-4 times
   faster than the optimized twoway_strstr.  */
static char *
basic_strstr (const char *s1, const char *s2)
{
  size_t i;
  int c = s2[0];

  if (c == 0)
    return (char*)s1;

  for ( ; s1[0] != '\0'; s1++)
    {
      if (s1[0] != c)
	continue;
      for (i = 1; s2[i] != 0; i++)
	if (s1[i] != s2[i])
	  break;
      if (s2[i] == '\0')
	return (char*)s1;
    }

  return NULL;
}

#define RETURN_TYPE char *
#define AVAILABLE(h, h_l, j, n_l)			\
  (((j) + (n_l) <= (h_l)) \
   || ((h_l) += __strnlen ((void*)((h) + (h_l)), (n_l) + 512), \
       (j) + (n_l) <= (h_l)))
#define CHECK_EOL (1)
#define RET0_IF_0(a) if (!a) goto ret0
#define FASTSEARCH(S,C,N) (void*) strchr ((void*)(S), (C))
#define LONG_NEEDLE_THRESHOLD 32U
#define __strnlen strnlen
#include "string/str-two-way.h"

/* Optimized Two-way implementation from GLIBC 2.29.  */
static char *
twoway_strstr (const char *haystack, const char *needle)
{
  size_t needle_len; /* Length of NEEDLE.  */
  size_t haystack_len; /* Known minimum length of HAYSTACK.  */

  /* Handle empty NEEDLE special case.  */
  if (needle[0] == '\0')
    return (char *) haystack;

  /* Skip until we find the first matching char from NEEDLE.  */
  haystack = strchr (haystack, needle[0]);
  if (haystack == NULL || needle[1] == '\0')
    return (char *) haystack;

  /* Ensure HAYSTACK length is at least as long as NEEDLE length.
     Since a match may occur early on in a huge HAYSTACK, use strnlen
     and read ahead a few cachelines for improved performance.  */
  needle_len = strlen (needle);
  haystack_len = __strnlen (haystack, needle_len + 256);
  if (haystack_len < needle_len)
    return NULL;

  /* Check whether we have a match.  This improves performance since we avoid
     the initialization overhead of the two-way algorithm.  */
  if (memcmp (haystack, needle, needle_len) == 0)
    return (char *) haystack;

  /* Perform the search.  Abstract memory is considered to be an array
     of 'unsigned char' values, not an array of 'char' values.  See
     ISO C 99 section 6.2.6.1.  */
  if (needle_len < LONG_NEEDLE_THRESHOLD)
    return two_way_short_needle ((const unsigned char *) haystack,
				  haystack_len,
				 (const unsigned char *) needle, needle_len);
  return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
			      (const unsigned char *) needle, needle_len);
}

typedef char *(*proto_t) (const char *, const char *);

IMPL (strstr, 1)
IMPL (twoway_strstr, 0)
IMPL (basic_strstr, 0)

static void
do_one_test (impl_t *impl, const char *s1, const char *s2, char *exp_result)
{
  size_t i, iters = INNER_LOOP_ITERS_SMALL / 8;
  timing_t start, stop, cur;
  char *res;

  TIMING_NOW (start);
  for (i = 0; i < iters; ++i)
    res = CALL (impl, s1, s2);
  TIMING_NOW (stop);

  TIMING_DIFF (cur, start, stop);

  TIMING_PRINT_MEAN ((double) cur, (double) iters);

  if (res != exp_result)
    {
      error (0, 0, "Wrong result in function %s %s %s", impl->name,
	     (res == NULL) ? "(null)" : res,
	     (exp_result == NULL) ? "(null)" : exp_result);
      ret = 1;
    }
}


static void
do_test (size_t align1, size_t align2, size_t len1, size_t len2,
	 int fail)
{
  char *s1 = (char *) (buf1 + align1);
  char *s2 = (char *) (buf2 + align2);

  size_t size = sizeof (input) - 1;
  size_t pos = (len1 + len2) % size;

  char *ss2 = s2;
  for (size_t l = len2; l > 0; l = l > size ? l - size : 0)
    {
      size_t t = l > size ? size : l;
      if (pos + t <= size)
	ss2 = mempcpy (ss2, input + pos, t);
      else
	{
	  ss2 = mempcpy (ss2, input + pos, size - pos);
	  ss2 = mempcpy (ss2, input, t - (size - pos));
	}
    }
  s2[len2] = '\0';

  char *ss1 = s1;
  for (size_t l = len1; l > 0; l = l > size ? l - size : 0)
    {
      size_t t = l > size ? size : l;
      memcpy (ss1, input, t);
      ss1 += t;
    }

  if (!fail)
    memcpy (s1 + len1 - len2, s2, len2);
  s1[len1] = '\0';

  /* Remove any accidental matches except for the last if !fail.  */
  for (ss1 = basic_strstr (s1, s2); ss1; ss1 = basic_strstr (ss1 + 1, s2))
    if (fail || ss1 != s1 + len1 - len2)
      ++ss1[len2 / 2];

  printf ("Length %4zd/%3zd, alignment %2zd/%2zd, %s:",
	  len1, len2, align1, align2, fail ? "fail " : "found");

  FOR_EACH_IMPL (impl, 0)
    do_one_test (impl, s1, s2, fail ? NULL : s1 + len1 - len2);

  putchar ('\n');
}

/* Test needles which exhibit worst-case performance.  This shows that
   basic_strstr is quadratic and thus unsuitable for large needles.
   On the other hand Two-way and skip table implementations are linear with
   increasing needle sizes.  The slowest cases of the two implementations are
   within a factor of 2 on several different microarchitectures.  */

static void
test_hard_needle (size_t ne_len, size_t hs_len)
{
  char *ne = (char *) buf1;
  char *hs = (char *) buf2;

  /* Hard needle for strstr algorithm using skip table.  This results in many
     memcmp calls comparing most of the needle.  */
  {
    memset (ne, 'a', ne_len);
    ne[ne_len] = '\0';
    ne[ne_len - 14] = 'b';

    memset (hs, 'a', hs_len);
    for (size_t i = ne_len; i <= hs_len; i += ne_len)
      {
	hs[i-5] = 'b';
	hs[i-62] = 'b';
      }

    printf ("Length %4zd/%3zd, complex needle 1:", hs_len, ne_len);

    FOR_EACH_IMPL (impl, 0)
      do_one_test (impl, hs, ne, NULL);
    putchar ('\n');
  }

  /* 2nd hard needle for strstr algorithm using skip table.  This results in
     many memcmp calls comparing most of the needle.  */
  {
    memset (ne, 'a', ne_len);
    ne[ne_len] = '\0';
    ne[ne_len - 6] = 'b';

    memset (hs, 'a', hs_len);
    for (size_t i = ne_len; i <= hs_len; i += ne_len)
      {
	hs[i-5] = 'b';
	hs[i-6] = 'b';
      }

    printf ("Length %4zd/%3zd, complex needle 2:", hs_len, ne_len);

    FOR_EACH_IMPL (impl, 0)
      do_one_test (impl, hs, ne, NULL);
    putchar ('\n');
  }

  /* Hard needle for Two-way algorithm - the random input causes a large number
     of branch mispredictions which significantly reduces performance on modern
     micro architectures.  */
  {
    for (int i = 0; i < hs_len; i++)
      hs[i] = (rand () & 255) > 155 ? 'a' : 'b';
    hs[hs_len] = 0;

    memset (ne, 'a', ne_len);
    ne[ne_len-2] = 'b';
    ne[0] = 'b';
    ne[ne_len] = 0;

    printf ("Length %4zd/%3zd, complex needle 3:", hs_len, ne_len);

    FOR_EACH_IMPL (impl, 0)
      do_one_test (impl, hs, ne, NULL);
    putchar ('\n');
  }
}

static int
test_main (void)
{
  test_init ();

  printf ("%23s", "");
  FOR_EACH_IMPL (impl, 0)
    printf ("\t%s", impl->name);
  putchar ('\n');

  for (size_t hlen = 64; hlen <= 256; hlen += 32)
    for (size_t klen = 1; klen <= 16; klen++)
      {
	do_test (1, 3, hlen, klen, 0);
	do_test (0, 9, hlen, klen, 1);
      }

  for (size_t hlen = 256; hlen <= 65536; hlen *= 2)
    for (size_t klen = 16; klen <= 256; klen *= 2)
      {
	do_test (1, 11, hlen, klen, 0);
	do_test (14, 5, hlen, klen, 1);
      }

  test_hard_needle (64, 65536);
  test_hard_needle (256, 65536);
  test_hard_needle (1024, 65536);

  return ret;
}

#include <support/test-driver.c>