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| 1 /* Byte-wise substring search, using the Two-Way algorithm. | |
| 2 Copyright (C) 2008, 2009, 2010, 2011 Free Software Foundation, Inc. | |
| 3 This file is part of the GNU C Library. | |
| 4 Written by Eric Blake <ebb9@byu.net>, 2008. | |
| 5 | |
| 6 This program is free software; you can redistribute it and/or modify | |
| 7 it under the terms of the GNU General Public License as published by | |
| 8 the Free Software Foundation; either version 3, or (at your option) | |
| 9 any later version. | |
| 10 | |
| 11 This program is distributed in the hope that it will be useful, | |
| 12 but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| 14 GNU General Public License for more details. | |
| 15 | |
| 16 You should have received a copy of the GNU General Public License along | |
| 17 with this program; if not, write to the Free Software Foundation, | |
| 18 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ | |
| 19 | |
| 20 /* Before including this file, you need to include <config.h> and | |
| 21 <string.h>, and define: | |
| 22 RESULT_TYPE A macro that expands to the return type. | |
| 23 AVAILABLE(h, h_l, j, n_l) | |
| 24 A macro that returns nonzero if there are | |
| 25 at least N_L bytes left starting at H[J]. | |
| 26 H is 'unsigned char *', H_L, J, and N_L | |
| 27 are 'size_t'; H_L is an lvalue. For | |
| 28 NUL-terminated searches, H_L can be | |
| 29 modified each iteration to avoid having | |
| 30 to compute the end of H up front. | |
| 31 | |
| 32 For case-insensitivity, you may optionally define: | |
| 33 CMP_FUNC(p1, p2, l) A macro that returns 0 iff the first L | |
| 34 characters of P1 and P2 are equal. | |
| 35 CANON_ELEMENT(c) A macro that canonicalizes an element right after | |
| 36 it has been fetched from one of the two strings. | |
| 37 The argument is an 'unsigned char'; the result | |
| 38 must be an 'unsigned char' as well. | |
| 39 | |
| 40 This file undefines the macros documented above, and defines | |
| 41 LONG_NEEDLE_THRESHOLD. | |
| 42 */ | |
| 43 | |
| 44 #include <limits.h> | |
| 45 #include <stdint.h> | |
| 46 | |
| 47 /* We use the Two-Way string matching algorithm, which guarantees | |
| 48 linear complexity with constant space. Additionally, for long | |
| 49 needles, we also use a bad character shift table similar to the | |
| 50 Boyer-Moore algorithm to achieve improved (potentially sub-linear) | |
| 51 performance. | |
| 52 | |
| 53 See http://www-igm.univ-mlv.fr/~lecroq/string/node26.html#SECTION00260 | |
| 54 and http://en.wikipedia.org/wiki/Boyer-Moore_string_search_algorithm | |
| 55 */ | |
| 56 | |
| 57 /* Point at which computing a bad-byte shift table is likely to be | |
| 58 worthwhile. Small needles should not compute a table, since it | |
| 59 adds (1 << CHAR_BIT) + NEEDLE_LEN computations of preparation for a | |
| 60 speedup no greater than a factor of NEEDLE_LEN. The larger the | |
| 61 needle, the better the potential performance gain. On the other | |
| 62 hand, on non-POSIX systems with CHAR_BIT larger than eight, the | |
| 63 memory required for the table is prohibitive. */ | |
| 64 #if CHAR_BIT < 10 | |
| 65 # define LONG_NEEDLE_THRESHOLD 32U | |
| 66 #else | |
| 67 # define LONG_NEEDLE_THRESHOLD SIZE_MAX | |
| 68 #endif | |
| 69 | |
| 70 #ifndef MAX | |
| 71 # define MAX(a, b) ((a < b) ? (b) : (a)) | |
| 72 #endif | |
| 73 | |
| 74 #ifndef CANON_ELEMENT | |
| 75 # define CANON_ELEMENT(c) c | |
| 76 #endif | |
| 77 #ifndef CMP_FUNC | |
| 78 # define CMP_FUNC memcmp | |
| 79 #endif | |
| 80 | |
| 81 /* Perform a critical factorization of NEEDLE, of length NEEDLE_LEN. | |
| 82 Return the index of the first byte in the right half, and set | |
| 83 *PERIOD to the global period of the right half. | |
| 84 | |
| 85 The global period of a string is the smallest index (possibly its | |
| 86 length) at which all remaining bytes in the string are repetitions | |
| 87 of the prefix (the last repetition may be a subset of the prefix). | |
| 88 | |
| 89 When NEEDLE is factored into two halves, a local period is the | |
| 90 length of the smallest word that shares a suffix with the left half | |
| 91 and shares a prefix with the right half. All factorizations of a | |
| 92 non-empty NEEDLE have a local period of at least 1 and no greater | |
| 93 than NEEDLE_LEN. | |
| 94 | |
| 95 A critical factorization has the property that the local period | |
| 96 equals the global period. All strings have at least one critical | |
| 97 factorization with the left half smaller than the global period. | |
| 98 | |
| 99 Given an ordered alphabet, a critical factorization can be computed | |
| 100 in linear time, with 2 * NEEDLE_LEN comparisons, by computing the | |
| 101 larger of two ordered maximal suffixes. The ordered maximal | |
| 102 suffixes are determined by lexicographic comparison of | |
| 103 periodicity. */ | |
| 104 static size_t | |
| 105 critical_factorization (const unsigned char *needle, size_t needle_len, | |
| 106 size_t *period) | |
| 107 { | |
| 108 /* Index of last byte of left half, or SIZE_MAX. */ | |
| 109 size_t max_suffix, max_suffix_rev; | |
| 110 size_t j; /* Index into NEEDLE for current candidate suffix. */ | |
| 111 size_t k; /* Offset into current period. */ | |
| 112 size_t p; /* Intermediate period. */ | |
| 113 unsigned char a, b; /* Current comparison bytes. */ | |
| 114 | |
| 115 /* Invariants: | |
| 116 0 <= j < NEEDLE_LEN - 1 | |
| 117 -1 <= max_suffix{,_rev} < j (treating SIZE_MAX as if it were signed) | |
| 118 min(max_suffix, max_suffix_rev) < global period of NEEDLE | |
| 119 1 <= p <= global period of NEEDLE | |
| 120 p == global period of the substring NEEDLE[max_suffix{,_rev}+1...j] | |
| 121 1 <= k <= p | |
| 122 */ | |
| 123 | |
| 124 /* Perform lexicographic search. */ | |
| 125 max_suffix = SIZE_MAX; | |
| 126 j = 0; | |
| 127 k = p = 1; | |
| 128 while (j + k < needle_len) | |
| 129 { | |
| 130 a = CANON_ELEMENT (needle[j + k]); | |
| 131 b = CANON_ELEMENT (needle[max_suffix + k]); | |
| 132 if (a < b) | |
| 133 { | |
| 134 /* Suffix is smaller, period is entire prefix so far. */ | |
| 135 j += k; | |
| 136 k = 1; | |
| 137 p = j - max_suffix; | |
| 138 } | |
| 139 else if (a == b) | |
| 140 { | |
| 141 /* Advance through repetition of the current period. */ | |
| 142 if (k != p) | |
| 143 ++k; | |
| 144 else | |
| 145 { | |
| 146 j += p; | |
| 147 k = 1; | |
| 148 } | |
| 149 } | |
| 150 else /* b < a */ | |
| 151 { | |
| 152 /* Suffix is larger, start over from current location. */ | |
| 153 max_suffix = j++; | |
| 154 k = p = 1; | |
| 155 } | |
| 156 } | |
| 157 *period = p; | |
| 158 | |
| 159 /* Perform reverse lexicographic search. */ | |
| 160 max_suffix_rev = SIZE_MAX; | |
| 161 j = 0; | |
| 162 k = p = 1; | |
| 163 while (j + k < needle_len) | |
| 164 { | |
| 165 a = CANON_ELEMENT (needle[j + k]); | |
| 166 b = CANON_ELEMENT (needle[max_suffix_rev + k]); | |
| 167 if (b < a) | |
| 168 { | |
| 169 /* Suffix is smaller, period is entire prefix so far. */ | |
| 170 j += k; | |
| 171 k = 1; | |
| 172 p = j - max_suffix_rev; | |
| 173 } | |
| 174 else if (a == b) | |
| 175 { | |
| 176 /* Advance through repetition of the current period. */ | |
| 177 if (k != p) | |
| 178 ++k; | |
| 179 else | |
| 180 { | |
| 181 j += p; | |
| 182 k = 1; | |
| 183 } | |
| 184 } | |
| 185 else /* a < b */ | |
| 186 { | |
| 187 /* Suffix is larger, start over from current location. */ | |
| 188 max_suffix_rev = j++; | |
| 189 k = p = 1; | |
| 190 } | |
| 191 } | |
| 192 | |
| 193 /* Choose the longer suffix. Return the first byte of the right | |
| 194 half, rather than the last byte of the left half. */ | |
| 195 if (max_suffix_rev + 1 < max_suffix + 1) | |
| 196 return max_suffix + 1; | |
| 197 *period = p; | |
| 198 return max_suffix_rev + 1; | |
| 199 } | |
| 200 | |
| 201 /* Return the first location of non-empty NEEDLE within HAYSTACK, or | |
| 202 NULL. HAYSTACK_LEN is the minimum known length of HAYSTACK. This | |
| 203 method is optimized for NEEDLE_LEN < LONG_NEEDLE_THRESHOLD. | |
| 204 Performance is guaranteed to be linear, with an initialization cost | |
| 205 of 2 * NEEDLE_LEN comparisons. | |
| 206 | |
| 207 If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at | |
| 208 most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching. | |
| 209 If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 * | |
| 210 HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching. */ | |
| 211 static RETURN_TYPE | |
| 212 two_way_short_needle (const unsigned char *haystack, size_t haystack_len, | |
| 213 const unsigned char *needle, size_t needle_len) | |
| 214 { | |
| 215 size_t i; /* Index into current byte of NEEDLE. */ | |
| 216 size_t j; /* Index into current window of HAYSTACK. */ | |
| 217 size_t period; /* The period of the right half of needle. */ | |
| 218 size_t suffix; /* The index of the right half of needle. */ | |
| 219 | |
| 220 /* Factor the needle into two halves, such that the left half is | |
| 221 smaller than the global period, and the right half is | |
| 222 periodic (with a period as large as NEEDLE_LEN - suffix). */ | |
| 223 suffix = critical_factorization (needle, needle_len, &period); | |
| 224 | |
| 225 /* Perform the search. Each iteration compares the right half | |
| 226 first. */ | |
| 227 if (CMP_FUNC (needle, needle + period, suffix) == 0) | |
| 228 { | |
| 229 /* Entire needle is periodic; a mismatch can only advance by the | |
| 230 period, so use memory to avoid rescanning known occurrences | |
| 231 of the period. */ | |
| 232 size_t memory = 0; | |
| 233 j = 0; | |
| 234 while (AVAILABLE (haystack, haystack_len, j, needle_len)) | |
| 235 { | |
| 236 /* Scan for matches in right half. */ | |
| 237 i = MAX (suffix, memory); | |
| 238 while (i < needle_len && (CANON_ELEMENT (needle[i]) | |
| 239 == CANON_ELEMENT (haystack[i + j]))) | |
| 240 ++i; | |
| 241 if (needle_len <= i) | |
| 242 { | |
| 243 /* Scan for matches in left half. */ | |
| 244 i = suffix - 1; | |
| 245 while (memory < i + 1 && (CANON_ELEMENT (needle[i]) | |
| 246 == CANON_ELEMENT (haystack[i + j]))) | |
| 247 --i; | |
| 248 if (i + 1 < memory + 1) | |
| 249 return (RETURN_TYPE) (haystack + j); | |
| 250 /* No match, so remember how many repetitions of period | |
| 251 on the right half were scanned. */ | |
| 252 j += period; | |
| 253 memory = needle_len - period; | |
| 254 } | |
| 255 else | |
| 256 { | |
| 257 j += i - suffix + 1; | |
| 258 memory = 0; | |
| 259 } | |
| 260 } | |
| 261 } | |
| 262 else | |
| 263 { | |
| 264 /* The two halves of needle are distinct; no extra memory is | |
| 265 required, and any mismatch results in a maximal shift. */ | |
| 266 period = MAX (suffix, needle_len - suffix) + 1; | |
| 267 j = 0; | |
| 268 while (AVAILABLE (haystack, haystack_len, j, needle_len)) | |
| 269 { | |
| 270 /* Scan for matches in right half. */ | |
| 271 i = suffix; | |
| 272 while (i < needle_len && (CANON_ELEMENT (needle[i]) | |
| 273 == CANON_ELEMENT (haystack[i + j]))) | |
| 274 ++i; | |
| 275 if (needle_len <= i) | |
| 276 { | |
| 277 /* Scan for matches in left half. */ | |
| 278 i = suffix - 1; | |
| 279 while (i != SIZE_MAX && (CANON_ELEMENT (needle[i]) | |
| 280 == CANON_ELEMENT (haystack[i + j]))) | |
| 281 --i; | |
| 282 if (i == SIZE_MAX) | |
| 283 return (RETURN_TYPE) (haystack + j); | |
| 284 j += period; | |
| 285 } | |
| 286 else | |
| 287 j += i - suffix + 1; | |
| 288 } | |
| 289 } | |
| 290 return NULL; | |
| 291 } | |
| 292 | |
| 293 /* Return the first location of non-empty NEEDLE within HAYSTACK, or | |
| 294 NULL. HAYSTACK_LEN is the minimum known length of HAYSTACK. This | |
| 295 method is optimized for LONG_NEEDLE_THRESHOLD <= NEEDLE_LEN. | |
| 296 Performance is guaranteed to be linear, with an initialization cost | |
| 297 of 3 * NEEDLE_LEN + (1 << CHAR_BIT) operations. | |
| 298 | |
| 299 If AVAILABLE does not modify HAYSTACK_LEN (as in memmem), then at | |
| 300 most 2 * HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching, | |
| 301 and sublinear performance O(HAYSTACK_LEN / NEEDLE_LEN) is possible. | |
| 302 If AVAILABLE modifies HAYSTACK_LEN (as in strstr), then at most 3 * | |
| 303 HAYSTACK_LEN - NEEDLE_LEN comparisons occur in searching, and | |
| 304 sublinear performance is not possible. */ | |
| 305 static RETURN_TYPE | |
| 306 two_way_long_needle (const unsigned char *haystack, size_t haystack_len, | |
| 307 const unsigned char *needle, size_t needle_len) | |
| 308 { | |
| 309 size_t i; /* Index into current byte of NEEDLE. */ | |
| 310 size_t j; /* Index into current window of HAYSTACK. */ | |
| 311 size_t period; /* The period of the right half of needle. */ | |
| 312 size_t suffix; /* The index of the right half of needle. */ | |
| 313 size_t shift_table[1U << CHAR_BIT]; /* See below. */ | |
| 314 | |
| 315 /* Factor the needle into two halves, such that the left half is | |
| 316 smaller than the global period, and the right half is | |
| 317 periodic (with a period as large as NEEDLE_LEN - suffix). */ | |
| 318 suffix = critical_factorization (needle, needle_len, &period); | |
| 319 | |
| 320 /* Populate shift_table. For each possible byte value c, | |
| 321 shift_table[c] is the distance from the last occurrence of c to | |
| 322 the end of NEEDLE, or NEEDLE_LEN if c is absent from the NEEDLE. | |
| 323 shift_table[NEEDLE[NEEDLE_LEN - 1]] contains the only 0. */ | |
| 324 for (i = 0; i < 1U << CHAR_BIT; i++) | |
| 325 shift_table[i] = needle_len; | |
| 326 for (i = 0; i < needle_len; i++) | |
| 327 shift_table[CANON_ELEMENT (needle[i])] = needle_len - i - 1; | |
| 328 | |
| 329 /* Perform the search. Each iteration compares the right half | |
| 330 first. */ | |
| 331 if (CMP_FUNC (needle, needle + period, suffix) == 0) | |
| 332 { | |
| 333 /* Entire needle is periodic; a mismatch can only advance by the | |
| 334 period, so use memory to avoid rescanning known occurrences | |
| 335 of the period. */ | |
| 336 size_t memory = 0; | |
| 337 size_t shift; | |
| 338 j = 0; | |
| 339 while (AVAILABLE (haystack, haystack_len, j, needle_len)) | |
| 340 { | |
| 341 /* Check the last byte first; if it does not match, then | |
| 342 shift to the next possible match location. */ | |
| 343 shift = shift_table[CANON_ELEMENT (haystack[j + needle_len - 1])]; | |
| 344 if (0 < shift) | |
| 345 { | |
| 346 if (memory && shift < period) | |
| 347 { | |
| 348 /* Since needle is periodic, but the last period has | |
| 349 a byte out of place, there can be no match until | |
| 350 after the mismatch. */ | |
| 351 shift = needle_len - period; | |
| 352 memory = 0; | |
| 353 } | |
| 354 j += shift; | |
| 355 continue; | |
| 356 } | |
| 357 /* Scan for matches in right half. The last byte has | |
| 358 already been matched, by virtue of the shift table. */ | |
| 359 i = MAX (suffix, memory); | |
| 360 while (i < needle_len - 1 && (CANON_ELEMENT (needle[i]) | |
| 361 == CANON_ELEMENT (haystack[i + j]))) | |
| 362 ++i; | |
| 363 if (needle_len - 1 <= i) | |
| 364 { | |
| 365 /* Scan for matches in left half. */ | |
| 366 i = suffix - 1; | |
| 367 while (memory < i + 1 && (CANON_ELEMENT (needle[i]) | |
| 368 == CANON_ELEMENT (haystack[i + j]))) | |
| 369 --i; | |
| 370 if (i + 1 < memory + 1) | |
| 371 return (RETURN_TYPE) (haystack + j); | |
| 372 /* No match, so remember how many repetitions of period | |
| 373 on the right half were scanned. */ | |
| 374 j += period; | |
| 375 memory = needle_len - period; | |
| 376 } | |
| 377 else | |
| 378 { | |
| 379 j += i - suffix + 1; | |
| 380 memory = 0; | |
| 381 } | |
| 382 } | |
| 383 } | |
| 384 else | |
| 385 { | |
| 386 /* The two halves of needle are distinct; no extra memory is | |
| 387 required, and any mismatch results in a maximal shift. */ | |
| 388 size_t shift; | |
| 389 period = MAX (suffix, needle_len - suffix) + 1; | |
| 390 j = 0; | |
| 391 while (AVAILABLE (haystack, haystack_len, j, needle_len)) | |
| 392 { | |
| 393 /* Check the last byte first; if it does not match, then | |
| 394 shift to the next possible match location. */ | |
| 395 shift = shift_table[CANON_ELEMENT (haystack[j + needle_len - 1])]; | |
| 396 if (0 < shift) | |
| 397 { | |
| 398 j += shift; | |
| 399 continue; | |
| 400 } | |
| 401 /* Scan for matches in right half. The last byte has | |
| 402 already been matched, by virtue of the shift table. */ | |
| 403 i = suffix; | |
| 404 while (i < needle_len - 1 && (CANON_ELEMENT (needle[i]) | |
| 405 == CANON_ELEMENT (haystack[i + j]))) | |
| 406 ++i; | |
| 407 if (needle_len - 1 <= i) | |
| 408 { | |
| 409 /* Scan for matches in left half. */ | |
| 410 i = suffix - 1; | |
| 411 while (i != SIZE_MAX && (CANON_ELEMENT (needle[i]) | |
| 412 == CANON_ELEMENT (haystack[i + j]))) | |
| 413 --i; | |
| 414 if (i == SIZE_MAX) | |
| 415 return (RETURN_TYPE) (haystack + j); | |
| 416 j += period; | |
| 417 } | |
| 418 else | |
| 419 j += i - suffix + 1; | |
| 420 } | |
| 421 } | |
| 422 return NULL; | |
| 423 } | |
| 424 | |
| 425 #undef AVAILABLE | |
| 426 #undef CANON_ELEMENT | |
| 427 #undef CMP_FUNC | |
| 428 #undef MAX | |
| 429 #undef RETURN_TYPE | |
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Chromium Code Reviews
Issue 11969036:
Merge GDB 7.5.1 (Closed)
Base URL: http://git.chromium.org/native_client/nacl-gdb.git@master