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*/
1 /* Case-insensitive searching in a string. -*- coding: utf-8 -*-
2 Copyright (C) 2005-2021 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2005.
4
5 This file is free software: you can redistribute it and/or modify
6 it under the terms of the GNU Lesser General Public License as
7 published by the Free Software Foundation; either version 3 of the
8 License, or (at your option) any later version.
9
10 This file 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
13 GNU Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public License
16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
17
18 #include <config.h>
19
20 /* Specification. */
21 #include <string.h>
22
23 #include <ctype.h>
24 #include <stdbool.h>
25 #include <stddef.h> /* for NULL, in case a nonstandard string.h lacks it */
26 #include <stdlib.h>
27
28 #include "malloca.h"
29 #include "mbuiter.h"
30
31 #define TOLOWER(Ch) (isupper (Ch) ? tolower (Ch) : (Ch))
32
33 /* Knuth-Morris-Pratt algorithm. */
34 #define UNIT unsigned char
35 #define CANON_ELEMENT(c) TOLOWER (c)
36 #include "str-kmp.h"
37
38 /* Knuth-Morris-Pratt algorithm.
39 See https://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm
40 Return a boolean indicating success:
41 Return true and set *RESULTP if the search was completed.
42 Return false if it was aborted because not enough memory was available. */
43 static bool
44 knuth_morris_pratt_multibyte (const char *haystack, const char *needle,
/* ![[next]](../icons/right.png)
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*/
45 const char **resultp)
46 {
47 size_t m = mbslen (needle);
48 mbchar_t *needle_mbchars;
49 size_t *table;
50
51 /* Allocate room for needle_mbchars and the table. */
52 char *memory = (char *) nmalloca (m, sizeof (mbchar_t) + sizeof (size_t));
53 if (memory == NULL)
54 return false;
55 needle_mbchars = (mbchar_t *) memory;
56 table = (size_t *) (memory + m * sizeof (mbchar_t));
57
58 /* Fill needle_mbchars. */
59 {
60 mbui_iterator_t iter;
61 size_t j;
62
63 j = 0;
64 for (mbui_init (iter, needle); mbui_avail (iter); mbui_advance (iter), j++)
65 {
66 mb_copy (&needle_mbchars[j], &mbui_cur (iter));
67 if (needle_mbchars[j].wc_valid)
68 needle_mbchars[j].wc = towlower (needle_mbchars[j].wc);
69 }
70 }
71
72 /* Fill the table.
73 For 0 < i < m:
74 0 < table[i] <= i is defined such that
75 forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x],
76 and table[i] is as large as possible with this property.
77 This implies:
78 1) For 0 < i < m:
79 If table[i] < i,
80 needle[table[i]..i-1] = needle[0..i-1-table[i]].
81 2) For 0 < i < m:
82 rhaystack[0..i-1] == needle[0..i-1]
83 and exists h, i <= h < m: rhaystack[h] != needle[h]
84 implies
85 forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1].
86 table[0] remains uninitialized. */
87 {
88 size_t i, j;
89
90 /* i = 1: Nothing to verify for x = 0. */
91 table[1] = 1;
92 j = 0;
93
94 for (i = 2; i < m; i++)
95 {
96 /* Here: j = i-1 - table[i-1].
97 The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold
98 for x < table[i-1], by induction.
99 Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */
100 mbchar_t *b = &needle_mbchars[i - 1];
101
102 for (;;)
103 {
104 /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x]
105 is known to hold for x < i-1-j.
106 Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */
107 if (mb_equal (*b, needle_mbchars[j]))
108 {
109 /* Set table[i] := i-1-j. */
110 table[i] = i - ++j;
111 break;
112 }
113 /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
114 for x = i-1-j, because
115 needle[i-1] != needle[j] = needle[i-1-x]. */
116 if (j == 0)
117 {
118 /* The inequality holds for all possible x. */
119 table[i] = i;
120 break;
121 }
122 /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
123 for i-1-j < x < i-1-j+table[j], because for these x:
124 needle[x..i-2]
125 = needle[x-(i-1-j)..j-1]
126 != needle[0..j-1-(x-(i-1-j))] (by definition of table[j])
127 = needle[0..i-2-x],
128 hence needle[x..i-1] != needle[0..i-1-x].
129 Furthermore
130 needle[i-1-j+table[j]..i-2]
131 = needle[table[j]..j-1]
132 = needle[0..j-1-table[j]] (by definition of table[j]). */
133 j = j - table[j];
134 }
135 /* Here: j = i - table[i]. */
136 }
137 }
138
139 /* Search, using the table to accelerate the processing. */
140 {
141 size_t j;
142 mbui_iterator_t rhaystack;
143 mbui_iterator_t phaystack;
144
145 *resultp = NULL;
146 j = 0;
147 mbui_init (rhaystack, haystack);
148 mbui_init (phaystack, haystack);
149 /* Invariant: phaystack = rhaystack + j. */
150 while (mbui_avail (phaystack))
151 {
152 mbchar_t c;
153
154 mb_copy (&c, &mbui_cur (phaystack));
155 if (c.wc_valid)
156 c.wc = towlower (c.wc);
157 if (mb_equal (needle_mbchars[j], c))
158 {
159 j++;
160 mbui_advance (phaystack);
161 if (j == m)
162 {
163 /* The entire needle has been found. */
164 *resultp = mbui_cur_ptr (rhaystack);
165 break;
166 }
167 }
168 else if (j > 0)
169 {
170 /* Found a match of needle[0..j-1], mismatch at needle[j]. */
171 size_t count = table[j];
172 j -= count;
173 for (; count > 0; count--)
174 {
175 if (!mbui_avail (rhaystack))
176 abort ();
177 mbui_advance (rhaystack);
178 }
179 }
180 else
181 {
182 /* Found a mismatch at needle[0] already. */
183 if (!mbui_avail (rhaystack))
184 abort ();
185 mbui_advance (rhaystack);
186 mbui_advance (phaystack);
187 }
188 }
189 }
190
191 freea (memory);
192 return true;
193 }
194
195 /* Find the first occurrence of the character string NEEDLE in the character
196 string HAYSTACK, using case-insensitive comparison.
197 Note: This function may, in multibyte locales, return success even if
198 strlen (haystack) < strlen (needle) ! */
199 char *
200 mbscasestr (const char *haystack, const char *needle)
/* ![[previous]](../icons/left.png)
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*/
201 {
202 /* Be careful not to look at the entire extent of haystack or needle
203 until needed. This is useful because of these two cases:
204 - haystack may be very long, and a match of needle found early,
205 - needle may be very long, and not even a short initial segment of
206 needle may be found in haystack. */
207 if (MB_CUR_MAX > 1)
208 {
209 mbui_iterator_t iter_needle;
210
211 mbui_init (iter_needle, needle);
212 if (mbui_avail (iter_needle))
213 {
214 /* Minimizing the worst-case complexity:
215 Let n = mbslen(haystack), m = mbslen(needle).
216 The naïve algorithm is O(n*m) worst-case.
217 The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a
218 memory allocation.
219 To achieve linear complexity and yet amortize the cost of the
220 memory allocation, we activate the Knuth-Morris-Pratt algorithm
221 only once the naïve algorithm has already run for some time; more
222 precisely, when
223 - the outer loop count is >= 10,
224 - the average number of comparisons per outer loop is >= 5,
225 - the total number of comparisons is >= m.
226 But we try it only once. If the memory allocation attempt failed,
227 we don't retry it. */
228 bool try_kmp = true;
229 size_t outer_loop_count = 0;
230 size_t comparison_count = 0;
231 size_t last_ccount = 0; /* last comparison count */
232 mbui_iterator_t iter_needle_last_ccount; /* = needle + last_ccount */
233
234 mbchar_t b;
235 mbui_iterator_t iter_haystack;
236
237 mbui_init (iter_needle_last_ccount, needle);
238
239 mb_copy (&b, &mbui_cur (iter_needle));
240 if (b.wc_valid)
241 b.wc = towlower (b.wc);
242
243 mbui_init (iter_haystack, haystack);
244 for (;; mbui_advance (iter_haystack))
245 {
246 mbchar_t c;
247
248 if (!mbui_avail (iter_haystack))
249 /* No match. */
250 return NULL;
251
252 /* See whether it's advisable to use an asymptotically faster
253 algorithm. */
254 if (try_kmp
255 && outer_loop_count >= 10
256 && comparison_count >= 5 * outer_loop_count)
257 {
258 /* See if needle + comparison_count now reaches the end of
259 needle. */
260 size_t count = comparison_count - last_ccount;
261 for (;
262 count > 0 && mbui_avail (iter_needle_last_ccount);
263 count--)
264 mbui_advance (iter_needle_last_ccount);
265 last_ccount = comparison_count;
266 if (!mbui_avail (iter_needle_last_ccount))
267 {
268 /* Try the Knuth-Morris-Pratt algorithm. */
269 const char *result;
270 bool success =
271 knuth_morris_pratt_multibyte (haystack, needle,
272 &result);
273 if (success)
274 return (char *) result;
275 try_kmp = false;
276 }
277 }
278
279 outer_loop_count++;
280 comparison_count++;
281 mb_copy (&c, &mbui_cur (iter_haystack));
282 if (c.wc_valid)
283 c.wc = towlower (c.wc);
284 if (mb_equal (c, b))
285 /* The first character matches. */
286 {
287 mbui_iterator_t rhaystack;
288 mbui_iterator_t rneedle;
289
290 memcpy (&rhaystack, &iter_haystack, sizeof (mbui_iterator_t));
291 mbui_advance (rhaystack);
292
293 mbui_init (rneedle, needle);
294 if (!mbui_avail (rneedle))
295 abort ();
296 mbui_advance (rneedle);
297
298 for (;; mbui_advance (rhaystack), mbui_advance (rneedle))
299 {
300 if (!mbui_avail (rneedle))
301 /* Found a match. */
302 return (char *) mbui_cur_ptr (iter_haystack);
303 if (!mbui_avail (rhaystack))
304 /* No match. */
305 return NULL;
306 comparison_count++;
307 if (!mb_caseequal (mbui_cur (rhaystack),
308 mbui_cur (rneedle)))
309 /* Nothing in this round. */
310 break;
311 }
312 }
313 }
314 }
315 else
316 return (char *) haystack;
317 }
318 else
319 {
320 if (*needle != '\0')
321 {
322 /* Minimizing the worst-case complexity:
323 Let n = strlen(haystack), m = strlen(needle).
324 The naïve algorithm is O(n*m) worst-case.
325 The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a
326 memory allocation.
327 To achieve linear complexity and yet amortize the cost of the
328 memory allocation, we activate the Knuth-Morris-Pratt algorithm
329 only once the naïve algorithm has already run for some time; more
330 precisely, when
331 - the outer loop count is >= 10,
332 - the average number of comparisons per outer loop is >= 5,
333 - the total number of comparisons is >= m.
334 But we try it only once. If the memory allocation attempt failed,
335 we don't retry it. */
336 bool try_kmp = true;
337 size_t outer_loop_count = 0;
338 size_t comparison_count = 0;
339 size_t last_ccount = 0; /* last comparison count */
340 const char *needle_last_ccount = needle; /* = needle + last_ccount */
341
342 /* Speed up the following searches of needle by caching its first
343 character. */
344 unsigned char b = TOLOWER ((unsigned char) *needle);
345
346 needle++;
347 for (;; haystack++)
348 {
349 if (*haystack == '\0')
350 /* No match. */
351 return NULL;
352
353 /* See whether it's advisable to use an asymptotically faster
354 algorithm. */
355 if (try_kmp
356 && outer_loop_count >= 10
357 && comparison_count >= 5 * outer_loop_count)
358 {
359 /* See if needle + comparison_count now reaches the end of
360 needle. */
361 if (needle_last_ccount != NULL)
362 {
363 needle_last_ccount +=
364 strnlen (needle_last_ccount,
365 comparison_count - last_ccount);
366 if (*needle_last_ccount == '\0')
367 needle_last_ccount = NULL;
368 last_ccount = comparison_count;
369 }
370 if (needle_last_ccount == NULL)
371 {
372 /* Try the Knuth-Morris-Pratt algorithm. */
373 const unsigned char *result;
374 bool success =
375 knuth_morris_pratt ((const unsigned char *) haystack,
376 (const unsigned char *) (needle - 1),
377 strlen (needle - 1),
378 &result);
379 if (success)
380 return (char *) result;
381 try_kmp = false;
382 }
383 }
384
385 outer_loop_count++;
386 comparison_count++;
387 if (TOLOWER ((unsigned char) *haystack) == b)
388 /* The first character matches. */
389 {
390 const char *rhaystack = haystack + 1;
391 const char *rneedle = needle;
392
393 for (;; rhaystack++, rneedle++)
394 {
395 if (*rneedle == '\0')
396 /* Found a match. */
397 return (char *) haystack;
398 if (*rhaystack == '\0')
399 /* No match. */
400 return NULL;
401 comparison_count++;
402 if (TOLOWER ((unsigned char) *rhaystack)
403 != TOLOWER ((unsigned char) *rneedle))
404 /* Nothing in this round. */
405 break;
406 }
407 }
408 }
409 }
410 else
411 return (char *) haystack;
412 }
413 }
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*/