lib/mbsstr.c

   1 /* Searching in a string.  -*- coding: utf-8 -*-
   2    Copyright (C) 2005-2025 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 <stddef.h>  /* for NULL, in case a nonstandard string.h lacks it */
  24 #include <stdlib.h>
  25
  26 #include "malloca.h"
  27
  28 #if GNULIB_MCEL_PREFER
  29 # include "mcel.h"
  30 typedef mcel_t mbchar_t;
  31 static bool mb_equal (mcel_t a, mcel_t b) { return mcel_cmp (a, b) == 0; }
  32 #else
  33 # include "mbuiter.h"
  34 #endif
  35
  36 /* Knuth-Morris-Pratt algorithm.  */
  37 #define UNIT unsigned char
  38 #define CANON_ELEMENT(c) c
  39 #include "str-kmp.h"
  40
  41 /* Knuth-Morris-Pratt algorithm.
  42    See https://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm
  43    Return a boolean indicating success:
  44    Return true and set *RESULTP if the search was completed.
  45    Return false if it was aborted because not enough memory was available.  */
  46 static bool
  47 knuth_morris_pratt_multibyte (const char *haystack, const char *needle,
  48                               const char **resultp)
  49 {
  50   size_t m = mbslen (needle);
  51   mbchar_t *needle_mbchars;
  52   size_t extra_align = (alignof (mbchar_t) < alignof (size_t)
  53                         ? alignof (size_t) - alignof (mbchar_t)
  54                         : 0);
  55
  56   /* Allocate room for needle_mbchars and the table.  */
  57   void *memory = nmalloca (m + !!extra_align,
  58                            sizeof (mbchar_t) + sizeof (size_t));
  59   void *table_memory;
  60   if (memory == NULL)
  61     return false;
  62   needle_mbchars = memory;
  63   table_memory = needle_mbchars + m;
  64   char *aligned = table_memory;
  65   aligned += extra_align;
  66   aligned -= (uintptr_t) aligned % alignof (size_t);
  67   size_t *table = table_memory = aligned;
  68
  69   /* Fill needle_mbchars.  */
  70 #if GNULIB_MCEL_PREFER
  71   for (size_t j = 0; *needle; needle += needle_mbchars[j++].len)
  72     needle_mbchars[j] = mcel_scanz (needle);
  73 #else
  74   {
  75     mbui_iterator_t iter;
  76     size_t j;
  77
  78     j = 0;
  79     for (mbui_init (iter, needle); mbui_avail (iter); mbui_advance (iter), j++)
  80       mb_copy (&needle_mbchars[j], &mbui_cur (iter));
  81   }
  82 #endif
  83
  84   /* Fill the table.
  85      For 0 < i < m:
  86        0 < table[i] <= i is defined such that
  87        forall 0 < x < table[i]: needle[x..i-1] != needle[0..i-1-x],
  88        and table[i] is as large as possible with this property.
  89      This implies:
  90      1) For 0 < i < m:
  91           If table[i] < i,
  92           needle[table[i]..i-1] = needle[0..i-1-table[i]].
  93      2) For 0 < i < m:
  94           rhaystack[0..i-1] == needle[0..i-1]
  95           and exists h, i <= h < m: rhaystack[h] != needle[h]
  96           implies
  97           forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1].
  98      table[0] remains uninitialized.  */
  99   {
 100     size_t i, j;
 101
 102     /* i = 1: Nothing to verify for x = 0.  */
 103     table[1] = 1;
 104     j = 0;
 105
 106     for (i = 2; i < m; i++)
 107       {
 108         /* Here: j = i-1 - table[i-1].
 109            The inequality needle[x..i-1] != needle[0..i-1-x] is known to hold
 110            for x < table[i-1], by induction.
 111            Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1].  */
 112         mbchar_t *b = &needle_mbchars[i - 1];
 113
 114         for (;;)
 115           {
 116             /* Invariants: The inequality needle[x..i-1] != needle[0..i-1-x]
 117                is known to hold for x < i-1-j.
 118                Furthermore, if j>0: needle[i-1-j..i-2] = needle[0..j-1].  */
 119             if (mb_equal (*b, needle_mbchars[j]))
 120               {
 121                 /* Set table[i] := i-1-j.  */
 122                 table[i] = i - ++j;
 123                 break;
 124               }
 125             /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
 126                for x = i-1-j, because
 127                  needle[i-1] != needle[j] = needle[i-1-x].  */
 128             if (j == 0)
 129               {
 130                 /* The inequality holds for all possible x.  */
 131                 table[i] = i;
 132                 break;
 133               }
 134             /* The inequality needle[x..i-1] != needle[0..i-1-x] also holds
 135                for i-1-j < x < i-1-j+table[j], because for these x:
 136                  needle[x..i-2]
 137                  = needle[x-(i-1-j)..j-1]
 138                  != needle[0..j-1-(x-(i-1-j))]  (by definition of table[j])
 139                     = needle[0..i-2-x],
 140                hence needle[x..i-1] != needle[0..i-1-x].
 141                Furthermore
 142                  needle[i-1-j+table[j]..i-2]
 143                  = needle[table[j]..j-1]
 144                  = needle[0..j-1-table[j]]  (by definition of table[j]).  */
 145             j = j - table[j];
 146           }
 147         /* Here: j = i - table[i].  */
 148       }
 149   }
 150
 151   /* Search, using the table to accelerate the processing.  */
 152   {
 153 #if GNULIB_MCEL_PREFER
 154     size_t j;
 155     char const *rhaystack = haystack;
 156     char const *phaystack = haystack;
 157
 158     j = 0;
 159     /* Invariant: phaystack = rhaystack + j.  */
 160     for (;;)
 161       {
 162         if (!*phaystack)
 163           {
 164             rhaystack = NULL;
 165             break;
 166           }
 167         mcel_t g = mcel_scanz (phaystack);
 168         if (mcel_cmp (needle_mbchars[j], g) == 0)
 169           {
 170             j++;
 171             /* Exit loop successfully if the entire needle has been found.  */
 172             if (j == m)
 173               break;
 174             phaystack += g.len;
 175           }
 176         else if (j == 0)
 177           {
 178             /* Found a mismatch at needle[0] already.  */
 179             rhaystack += mcel_scanz (rhaystack).len;
 180             phaystack += g.len;
 181           }
 182         else
 183           {
 184             /* Found a match of needle[0..j-1], mismatch at needle[j].  */
 185             size_t count = table[j];
 186             j -= count;
 187             for (; count != 0; count--)
 188               rhaystack += mcel_scanz (rhaystack).len;
 189           }
 190       }
 191     *resultp = rhaystack;
 192 #else
 193     size_t j;
 194     mbui_iterator_t rhaystack;
 195     mbui_iterator_t phaystack;
 196
 197     *resultp = NULL;
 198     j = 0;
 199     mbui_init (rhaystack, haystack);
 200     mbui_init (phaystack, haystack);
 201     /* Invariant: phaystack = rhaystack + j.  */
 202     while (mbui_avail (phaystack))
 203       if (mb_equal (needle_mbchars[j], mbui_cur (phaystack)))
 204         {
 205           j++;
 206           mbui_advance (phaystack);
 207           if (j == m)
 208             {
 209               /* The entire needle has been found.  */
 210               *resultp = mbui_cur_ptr (rhaystack);
 211               break;
 212             }
 213         }
 214       else if (j > 0)
 215         {
 216           /* Found a match of needle[0..j-1], mismatch at needle[j].  */
 217           size_t count = table[j];
 218           j -= count;
 219           for (; count > 0; count--)
 220             {
 221               if (!mbui_avail (rhaystack))
 222                 abort ();
 223               mbui_advance (rhaystack);
 224             }
 225         }
 226       else
 227         {
 228           /* Found a mismatch at needle[0] already.  */
 229           if (!mbui_avail (rhaystack))
 230             abort ();
 231           mbui_advance (rhaystack);
 232           mbui_advance (phaystack);
 233         }
 234 #endif
 235   }
 236
 237   freea (memory);
 238   return true;
 239 }
 240
 241 /* Find the first occurrence of the character string NEEDLE in the character
 242    string HAYSTACK.  Return NULL if NEEDLE is not found in HAYSTACK.  */
 243 char *
 244 mbsstr (const char *haystack, const char *needle)
 245 {
 246   /* Be careful not to look at the entire extent of haystack or needle
 247      until needed.  This is useful because of these two cases:
 248        - haystack may be very long, and a match of needle found early,
 249        - needle may be very long, and not even a short initial segment of
 250          needle may be found in haystack.  */
 251   if (MB_CUR_MAX > 1)
 252     {
 253 #if GNULIB_MCEL_PREFER
 254       if (!*needle)
 255         return (char *) haystack;
 256
 257       mcel_t ng = mcel_scanz (needle);
 258
 259       /* Minimizing the worst-case complexity:
 260          Let n = mbslen(haystack), m = mbslen(needle).
 261          The naïve algorithm is O(n*m) worst-case.
 262          The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a
 263          memory allocation.
 264          To achieve linear complexity and yet amortize the cost of the
 265          memory allocation, we activate the Knuth-Morris-Pratt algorithm
 266          only once the naïve algorithm has already run for some time; more
 267          precisely, when
 268            - the outer loop count is >= 10,
 269            - the average number of comparisons per outer loop is >= 5,
 270            - the total number of comparisons is >= m.
 271          But we try it only once.  If the memory allocation attempt failed,
 272          we don't retry it.  */
 273       bool try_kmp = true;
 274       size_t outer_loop_count = 0;
 275       size_t comparison_count = 0;
 276
 277       /* Last comparison count, and needle + last_ccount.  */
 278       size_t last_ccount = 0;
 279       char const *iter_needle_last_ccount = needle;
 280
 281       char const *iter_haystack = haystack;
 282
 283       for (mcel_t hg; *iter_haystack; iter_haystack += hg.len)
 284         {
 285           /* See whether it's advisable to use an asymptotically faster
 286              algorithm.  */
 287           if (try_kmp
 288               && outer_loop_count >= 10
 289               && comparison_count >= 5 * outer_loop_count)
 290             {
 291               /* See if needle + comparison_count now reaches the end of
 292                  needle.  */
 293               size_t count = comparison_count - last_ccount;
 294               for (;
 295                    count > 0 && *iter_needle_last_ccount;
 296                    count--)
 297                 iter_needle_last_ccount
 298                   += mcel_scanz (iter_needle_last_ccount).len;
 299               last_ccount = comparison_count;
 300               if (!*iter_needle_last_ccount)
 301                 {
 302                   char const *result;
 303                   if (knuth_morris_pratt_multibyte (haystack, needle,
 304                                                     &result))
 305                     return (char *) result;
 306                   try_kmp = false;
 307                 }
 308             }
 309
 310           outer_loop_count++;
 311           comparison_count++;
 312           hg = mcel_scanz (iter_haystack);
 313           if (mcel_cmp (hg, ng) == 0)
 314             /* The first character matches.  */
 315             {
 316               char const *rhaystack = iter_haystack + hg.len;
 317               char const *rneedle = needle + ng.len;
 318               mcel_t rhg, rng;
 319               do
 320                 {
 321                   if (!*rneedle)
 322                     return (char *) iter_haystack;
 323                   if (!*rhaystack)
 324                     return NULL;
 325                   rhg = mcel_scanz (rhaystack); rhaystack += rhg.len;
 326                   rng = mcel_scanz (rneedle); rneedle += rng.len;
 327                   comparison_count++;
 328                 }
 329               while (mcel_cmp (rhg, rng) == 0);
 330             }
 331         }
 332
 333       return NULL;
 334 #else
 335       mbui_iterator_t iter_needle;
 336
 337       mbui_init (iter_needle, needle);
 338       if (mbui_avail (iter_needle))
 339         {
 340           /* Minimizing the worst-case complexity:
 341              Let n = mbslen(haystack), m = mbslen(needle).
 342              The naïve algorithm is O(n*m) worst-case.
 343              The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a
 344              memory allocation.
 345              To achieve linear complexity and yet amortize the cost of the
 346              memory allocation, we activate the Knuth-Morris-Pratt algorithm
 347              only once the naïve algorithm has already run for some time; more
 348              precisely, when
 349                - the outer loop count is >= 10,
 350                - the average number of comparisons per outer loop is >= 5,
 351                - the total number of comparisons is >= m.
 352              But we try it only once.  If the memory allocation attempt failed,
 353              we don't retry it.  */
 354           bool try_kmp = true;
 355           size_t outer_loop_count = 0;
 356           size_t comparison_count = 0;
 357           size_t last_ccount = 0;                  /* last comparison count */
 358           mbui_iterator_t iter_needle_last_ccount; /* = needle + last_ccount */
 359
 360           mbui_iterator_t iter_haystack;
 361
 362           mbui_init (iter_needle_last_ccount, needle);
 363           mbui_init (iter_haystack, haystack);
 364           for (;; mbui_advance (iter_haystack))
 365             {
 366               if (!mbui_avail (iter_haystack))
 367                 /* No match.  */
 368                 return NULL;
 369
 370               /* See whether it's advisable to use an asymptotically faster
 371                  algorithm.  */
 372               if (try_kmp
 373                   && outer_loop_count >= 10
 374                   && comparison_count >= 5 * outer_loop_count)
 375                 {
 376                   /* See if needle + comparison_count now reaches the end of
 377                      needle.  */
 378                   size_t count = comparison_count - last_ccount;
 379                   for (;
 380                        count > 0 && mbui_avail (iter_needle_last_ccount);
 381                        count--)
 382                     mbui_advance (iter_needle_last_ccount);
 383                   last_ccount = comparison_count;
 384                   if (!mbui_avail (iter_needle_last_ccount))
 385                     {
 386                       /* Try the Knuth-Morris-Pratt algorithm.  */
 387                       const char *result;
 388                       bool success =
 389                         knuth_morris_pratt_multibyte (haystack, needle,
 390                                                       &result);
 391                       if (success)
 392                         return (char *) result;
 393                       try_kmp = false;
 394                     }
 395                 }
 396
 397               outer_loop_count++;
 398               comparison_count++;
 399               if (mb_equal (mbui_cur (iter_haystack), mbui_cur (iter_needle)))
 400                 /* The first character matches.  */
 401                 {
 402                   mbui_iterator_t rhaystack;
 403                   mbui_iterator_t rneedle;
 404
 405                   memcpy (&rhaystack, &iter_haystack, sizeof (mbui_iterator_t));
 406                   mbui_advance (rhaystack);
 407
 408                   mbui_init (rneedle, needle);
 409                   if (!mbui_avail (rneedle))
 410                     abort ();
 411                   mbui_advance (rneedle);
 412
 413                   for (;; mbui_advance (rhaystack), mbui_advance (rneedle))
 414                     {
 415                       if (!mbui_avail (rneedle))
 416                         /* Found a match.  */
 417                         return (char *) mbui_cur_ptr (iter_haystack);
 418                       if (!mbui_avail (rhaystack))
 419                         /* No match.  */
 420                         return NULL;
 421                       comparison_count++;
 422                       if (!mb_equal (mbui_cur (rhaystack), mbui_cur (rneedle)))
 423                         /* Nothing in this round.  */
 424                         break;
 425                     }
 426                 }
 427             }
 428         }
 429       else
 430         return (char *) haystack;
 431 #endif
 432     }
 433   else
 434     {
 435       if (*needle != '\0')
 436         {
 437           /* Minimizing the worst-case complexity:
 438              Let n = strlen(haystack), m = strlen(needle).
 439              The naïve algorithm is O(n*m) worst-case.
 440              The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a
 441              memory allocation.
 442              To achieve linear complexity and yet amortize the cost of the
 443              memory allocation, we activate the Knuth-Morris-Pratt algorithm
 444              only once the naïve algorithm has already run for some time; more
 445              precisely, when
 446                - the outer loop count is >= 10,
 447                - the average number of comparisons per outer loop is >= 5,
 448                - the total number of comparisons is >= m.
 449              But we try it only once.  If the memory allocation attempt failed,
 450              we don't retry it.  */
 451           bool try_kmp = true;
 452           size_t outer_loop_count = 0;
 453           size_t comparison_count = 0;
 454           size_t last_ccount = 0;                  /* last comparison count */
 455           const char *needle_last_ccount = needle; /* = needle + last_ccount */
 456
 457           /* Speed up the following searches of needle by caching its first
 458              character.  */
 459           char b = *needle++;
 460
 461           for (;; haystack++)
 462             {
 463               if (*haystack == '\0')
 464                 /* No match.  */
 465                 return NULL;
 466
 467               /* See whether it's advisable to use an asymptotically faster
 468                  algorithm.  */
 469               if (try_kmp
 470                   && outer_loop_count >= 10
 471                   && comparison_count >= 5 * outer_loop_count)
 472                 {
 473                   /* See if needle + comparison_count now reaches the end of
 474                      needle.  */
 475                   if (needle_last_ccount != NULL)
 476                     {
 477                       needle_last_ccount +=
 478                         strnlen (needle_last_ccount,
 479                                  comparison_count - last_ccount);
 480                       if (*needle_last_ccount == '\0')
 481                         needle_last_ccount = NULL;
 482                       last_ccount = comparison_count;
 483                     }
 484                   if (needle_last_ccount == NULL)
 485                     {
 486                       /* Try the Knuth-Morris-Pratt algorithm.  */
 487                       const unsigned char *result;
 488                       bool success =
 489                         knuth_morris_pratt ((const unsigned char *) haystack,
 490                                             (const unsigned char *) (needle - 1),
 491                                             strlen (needle - 1),
 492                                             &result);
 493                       if (success)
 494                         return (char *) result;
 495                       try_kmp = false;
 496                     }
 497                 }
 498
 499               outer_loop_count++;
 500               comparison_count++;
 501               if (*haystack == b)
 502                 /* The first character matches.  */
 503                 {
 504                   const char *rhaystack = haystack + 1;
 505                   const char *rneedle = needle;
 506
 507                   for (;; rhaystack++, rneedle++)
 508                     {
 509                       if (*rneedle == '\0')
 510                         /* Found a match.  */
 511                         return (char *) haystack;
 512                       if (*rhaystack == '\0')
 513                         /* No match.  */
 514                         return NULL;
 515                       comparison_count++;
 516                       if (*rhaystack != *rneedle)
 517                         /* Nothing in this round.  */
 518                         break;
 519                     }
 520                 }
 521             }
 522         }
 523       else
 524         return (char *) haystack;
 525     }
 526 }