1 /* Measure strstr functions.
2 Copyright (C) 2013-2023 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>