lib/mbspcasecmp.c

   1 /* Case-insensitive string comparison function.
   2    Copyright (C) 1998-1999, 2005-2008, 2010-2024 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2007.
   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 <ctype.h>
  24 #include <stdlib.h>
  25
  26 #if GNULIB_MCEL_PREFER
  27 # include "mcel.h"
  28 #else
  29 # include "mbuiterf.h"
  30 #endif
  31
  32 /* Compare the initial segment of the character string STRING consisting of
  33    at most mbslen (PREFIX) characters with the character string PREFIX,
  34    ignoring case.  If the two match, return a pointer to the first byte
  35    after this prefix in STRING.  Otherwise, return NULL.
  36    Note: This function may, in multibyte locales, return non-NULL if STRING
  37    is of smaller length than PREFIX!  */
  38 char *
  39 mbspcasecmp (const char *string, const char *prefix)
  40 {
  41   /* This is essentially the same as
  42        mbsncasecmp (string, prefix, mbslen (prefix))
  43      just with small optimizations.  */
  44   if (string == prefix)
  45     return (char *) (string + strlen (string));
  46
  47   const char *iter1 = string;
  48   const char *iter2 = prefix;
  49
  50   /* Be careful not to look at the entire extent of STRING or PREFIX until
  51      needed.  This is useful because when two strings differ, the difference is
  52      most often already in the very few first characters.  */
  53   if (MB_CUR_MAX > 1)
  54     {
  55 #if GNULIB_MCEL_PREFER
  56       while (*iter2)
  57         {
  58           if (!*iter1)
  59             return NULL;
  60           mcel_t g1 = mcel_scanz (iter1); iter1 += g1.len;
  61           mcel_t g2 = mcel_scanz (iter2); iter2 += g2.len;
  62           if (mcel_tocmp (c32tolower, g1, g2) != 0)
  63             return NULL;
  64         }
  65       return (char *) iter1;
  66 #else
  67       mbuif_state_t state1;
  68       mbuif_init (state1);
  69
  70       mbuif_state_t state2;
  71       mbuif_init (state2);
  72
  73       while (mbuif_avail (state1, iter1) && mbuif_avail (state2, iter2))
  74         {
  75           mbchar_t cur1 = mbuif_next (state1, iter1);
  76           mbchar_t cur2 = mbuif_next (state2, iter2);
  77           int cmp = mb_casecmp (cur1, cur2);
  78
  79           if (cmp != 0)
  80             return NULL;
  81
  82           iter1 += mb_len (cur1);
  83           iter2 += mb_len (cur2);
  84         }
  85       if (!mbuif_avail (state2, iter2))
  86         /* PREFIX equals STRING or is terminated before STRING.  */
  87         return (char *) iter1;
  88       else
  89         /* STRING terminated before PREFIX.  */
  90         return NULL;
  91 #endif
  92     }
  93   else
  94     for (;; iter1++, iter2++)
  95       {
  96         unsigned char c2 = *iter2;
  97
  98         if (c2 == '\0')
  99           /* PREFIX equals STRING or is terminated before STRING.  */
 100           return (char *) iter1;
 101
 102         unsigned char c1 = *iter1;
 103
 104         if (c1 != c2)
 105           {
 106             c1 = tolower (c1);
 107             if (c1 != c2 && c1 != tolower (c2))
 108               /* STRING and PREFIX disagree,
 109                  or STRING terminated before PREFIX.  */
 110               return NULL;
 111           }
 112       }
 113 }