lib/mbsstr.c

   1 /* Searching in a string.  -*- coding: utf-8 -*-
   2    Copyright (C) 2005-2018 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
  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 https://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 }