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