1 /* Searching in a string. -*- coding: utf-8 -*- 2 Copyright (C) 2005-2015 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 <http://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 26 #include "malloca.h" 27 #include "mbuiter.h" 28 29 /* Knuth-Morris-Pratt algorithm. */ 30 #define UNIT unsigned char 31 #define CANON_ELEMENT(c) c 32 #include "str-kmp.h" 33 34 /* Knuth-Morris-Pratt algorithm. 35 See http://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm 36 Return a boolean indicating success: 37 Return true and set *RESULTP if the search was completed. 38 Return false if it was aborted because not enough memory was available. */ 39 static bool 40 knuth_morris_pratt_multibyte (const char *haystack, const char *needle, 41 const char **resultp) 42 { 43 size_t m = mbslen (needle); 44 mbchar_t *needle_mbchars; 45 size_t *table; 46 47 /* Allocate room for needle_mbchars and the table. */ 48 void *memory = nmalloca (m, sizeof (mbchar_t) + sizeof (size_t)); 49 void *table_memory; 50 if (memory == NULL) 51 return false; 52 needle_mbchars = memory; 53 table_memory = needle_mbchars + m; 54 table = table_memory; 55 56 /* Fill needle_mbchars. */ 57 { 58 mbui_iterator_t iter; 59 size_t j; 60 61 j = 0; 62 for (mbui_init (iter, needle); mbui_avail (iter); mbui_advance (iter), j++) 63 mb_copy (&needle_mbchars[j], &mbui_cur (iter)); 64 } 65 66 /* Fill the table. 67 For 0 < i < m: 68 0 < table[i] <= i is defined such that 69 forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x], 70 and table[i] is as large as possible with this property. 71 This implies: 72 1) For 0 < i < m: 73 If table[i] < i, 74 needle[table[i]..i-1] = needle[0..i-1-table[i]]. 75 2) For 0 < i < m: 76 rhaystack[0..i-1] == needle[0..i-1] 77 and exists h, i <= h < m: rhaystack[h] != needle[h] 78 implies 79 forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1]. 80 table[0] remains uninitialized. */ 81 { 82 size_t i, j; 83 84 /* i = 1: Nothing to verify for x = 0. */ 85 table[1] = 1; 86 j = 0; 87 88 for (i = 2; i < m; i++) 89 { 90 /* Here: j = i-1 - table[i-1]. 91 The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold 92 for x < table[i-1], by induction. 93 Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ 94 mbchar_t *b = &needle_mbchars[i - 1]; 95 96 for (;;) 97 { 98 /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x] 99 is known to hold for x < i-1-j. 100 Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1]. */ 101 if (mb_equal (*b, needle_mbchars[j])) 102 { 103 /* Set table[i] := i-1-j. */ 104 table[i] = i - ++j; 105 break; 106 } 107 /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds 108 for x = i-1-j, because 109 needle[i-1] != needle[j] = needle[i-1-x]. */ 110 if (j == 0) 111 { 112 /* The inequality holds for all possible x. */ 113 table[i] = i; 114 break; 115 } 116 /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds 117 for i-1-j < x < i-1-j+table[j], because for these x: 118 needle[x..i-2] 119 = needle[x-(i-1-j)..j-1] 120 != needle[0..j-1-(x-(i-1-j))] (by definition of table[j]) 121 = needle[0..i-2-x], 122 hence needle[x..i-1] != needle[0..i-1-x]. 123 Furthermore 124 needle[i-1-j+table[j]..i-2] 125 = needle[table[j]..j-1] 126 = needle[0..j-1-table[j]] (by definition of table[j]). */ 127 j = j - table[j]; 128 } 129 /* Here: j = i - table[i]. */ 130 } 131 } 132 133 /* Search, using the table to accelerate the processing. */ 134 { 135 size_t j; 136 mbui_iterator_t rhaystack; 137 mbui_iterator_t phaystack; 138 139 *resultp = NULL; 140 j = 0; 141 mbui_init (rhaystack, haystack); 142 mbui_init (phaystack, haystack); 143 /* Invariant: phaystack = rhaystack + j. */ 144 while (mbui_avail (phaystack)) 145 if (mb_equal (needle_mbchars[j], mbui_cur (phaystack))) 146 { 147 j++; 148 mbui_advance (phaystack); 149 if (j == m) 150 { 151 /* The entire needle has been found. */ 152 *resultp = mbui_cur_ptr (rhaystack); 153 break; 154 } 155 } 156 else if (j > 0) 157 { 158 /* Found a match of needle[0..j-1], mismatch at needle[j]. */ 159 size_t count = table[j]; 160 j -= count; 161 for (; count > 0; count--) 162 { 163 if (!mbui_avail (rhaystack)) 164 abort (); 165 mbui_advance (rhaystack); 166 } 167 } 168 else 169 { 170 /* Found a mismatch at needle[0] already. */ 171 if (!mbui_avail (rhaystack)) 172 abort (); 173 mbui_advance (rhaystack); 174 mbui_advance (phaystack); 175 } 176 } 177 178 freea (memory); 179 return true; 180 } 181 182 /* Find the first occurrence of the character string NEEDLE in the character 183 string HAYSTACK. Return NULL if NEEDLE is not found in HAYSTACK. */ 184 char * 185 mbsstr (const char *haystack, const char *needle) 186 { 187 /* Be careful not to look at the entire extent of haystack or needle 188 until needed. This is useful because of these two cases: 189 - haystack may be very long, and a match of needle found early, 190 - needle may be very long, and not even a short initial segment of 191 needle may be found in haystack. */ 192 if (MB_CUR_MAX > 1) 193 { 194 mbui_iterator_t iter_needle; 195 196 mbui_init (iter_needle, needle); 197 if (mbui_avail (iter_needle)) 198 { 199 /* Minimizing the worst-case complexity: 200 Let n = mbslen(haystack), m = mbslen(needle). 201 The naïve algorithm is O(n*m) worst-case. 202 The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a 203 memory allocation. 204 To achieve linear complexity and yet amortize the cost of the 205 memory allocation, we activate the Knuth-Morris-Pratt algorithm 206 only once the naïve algorithm has already run for some time; more 207 precisely, when 208 - the outer loop count is >= 10, 209 - the average number of comparisons per outer loop is >= 5, 210 - the total number of comparisons is >= m. 211 But we try it only once. If the memory allocation attempt failed, 212 we don't retry it. */ 213 bool try_kmp = true; 214 size_t outer_loop_count = 0; 215 size_t comparison_count = 0; 216 size_t last_ccount = 0; /* last comparison count */ 217 mbui_iterator_t iter_needle_last_ccount; /* = needle + last_ccount */ 218 219 mbui_iterator_t iter_haystack; 220 221 mbui_init (iter_needle_last_ccount, needle); 222 mbui_init (iter_haystack, haystack); 223 for (;; mbui_advance (iter_haystack)) 224 { 225 if (!mbui_avail (iter_haystack)) 226 /* No match. */ 227 return NULL; 228 229 /* See whether it's advisable to use an asymptotically faster 230 algorithm. */ 231 if (try_kmp 232 && outer_loop_count >= 10 233 && comparison_count >= 5 * outer_loop_count) 234 { 235 /* See if needle + comparison_count now reaches the end of 236 needle. */ 237 size_t count = comparison_count - last_ccount; 238 for (; 239 count > 0 && mbui_avail (iter_needle_last_ccount); 240 count--) 241 mbui_advance (iter_needle_last_ccount); 242 last_ccount = comparison_count; 243 if (!mbui_avail (iter_needle_last_ccount)) 244 { 245 /* Try the Knuth-Morris-Pratt algorithm. */ 246 const char *result; 247 bool success = 248 knuth_morris_pratt_multibyte (haystack, needle, 249 &result); 250 if (success) 251 return (char *) result; 252 try_kmp = false; 253 } 254 } 255 256 outer_loop_count++; 257 comparison_count++; 258 if (mb_equal (mbui_cur (iter_haystack), mbui_cur (iter_needle))) 259 /* The first character matches. */ 260 { 261 mbui_iterator_t rhaystack; 262 mbui_iterator_t rneedle; 263 264 memcpy (&rhaystack, &iter_haystack, sizeof (mbui_iterator_t)); 265 mbui_advance (rhaystack); 266 267 mbui_init (rneedle, needle); 268 if (!mbui_avail (rneedle)) 269 abort (); 270 mbui_advance (rneedle); 271 272 for (;; mbui_advance (rhaystack), mbui_advance (rneedle)) 273 { 274 if (!mbui_avail (rneedle)) 275 /* Found a match. */ 276 return (char *) mbui_cur_ptr (iter_haystack); 277 if (!mbui_avail (rhaystack)) 278 /* No match. */ 279 return NULL; 280 comparison_count++; 281 if (!mb_equal (mbui_cur (rhaystack), mbui_cur (rneedle))) 282 /* Nothing in this round. */ 283 break; 284 } 285 } 286 } 287 } 288 else 289 return (char *) haystack; 290 } 291 else 292 { 293 if (*needle != '\0') 294 { 295 /* Minimizing the worst-case complexity: 296 Let n = strlen(haystack), m = strlen(needle). 297 The naïve algorithm is O(n*m) worst-case. 298 The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a 299 memory allocation. 300 To achieve linear complexity and yet amortize the cost of the 301 memory allocation, we activate the Knuth-Morris-Pratt algorithm 302 only once the naïve algorithm has already run for some time; more 303 precisely, when 304 - the outer loop count is >= 10, 305 - the average number of comparisons per outer loop is >= 5, 306 - the total number of comparisons is >= m. 307 But we try it only once. If the memory allocation attempt failed, 308 we don't retry it. */ 309 bool try_kmp = true; 310 size_t outer_loop_count = 0; 311 size_t comparison_count = 0; 312 size_t last_ccount = 0; /* last comparison count */ 313 const char *needle_last_ccount = needle; /* = needle + last_ccount */ 314 315 /* Speed up the following searches of needle by caching its first 316 character. */ 317 char b = *needle++; 318 319 for (;; haystack++) 320 { 321 if (*haystack == '\0') 322 /* No match. */ 323 return NULL; 324 325 /* See whether it's advisable to use an asymptotically faster 326 algorithm. */ 327 if (try_kmp 328 && outer_loop_count >= 10 329 && comparison_count >= 5 * outer_loop_count) 330 { 331 /* See if needle + comparison_count now reaches the end of 332 needle. */ 333 if (needle_last_ccount != NULL) 334 { 335 needle_last_ccount += 336 strnlen (needle_last_ccount, 337 comparison_count - last_ccount); 338 if (*needle_last_ccount == '\0') 339 needle_last_ccount = NULL; 340 last_ccount = comparison_count; 341 } 342 if (needle_last_ccount == NULL) 343 { 344 /* Try the Knuth-Morris-Pratt algorithm. */ 345 const unsigned char *result; 346 bool success = 347 knuth_morris_pratt ((const unsigned char *) haystack, 348 (const unsigned char *) (needle - 1), 349 strlen (needle - 1), 350 &result); 351 if (success) 352 return (char *) result; 353 try_kmp = false; 354 } 355 } 356 357 outer_loop_count++; 358 comparison_count++; 359 if (*haystack == b) 360 /* The first character matches. */ 361 { 362 const char *rhaystack = haystack + 1; 363 const char *rneedle = needle; 364 365 for (;; rhaystack++, rneedle++) 366 { 367 if (*rneedle == '\0') 368 /* Found a match. */ 369 return (char *) haystack; 370 if (*rhaystack == '\0') 371 /* No match. */ 372 return NULL; 373 comparison_count++; 374 if (*rhaystack != *rneedle) 375 /* Nothing in this round. */ 376 break; 377 } 378 } 379 } 380 } 381 else 382 return (char *) haystack; 383 } 384 } 385