lib/mbspcasecmp.c

   1 /* Case-insensitive string comparison function.
   2    Copyright (C) 1998-1999, 2005-2008, 2010-2020 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2007.
   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 <ctype.h>
  24
  25 #include "mbuiter.h"
  26
  27 #define TOLOWER(Ch) (isupper (Ch) ? tolower (Ch) : (Ch))
  28
  29 /* Compare the initial segment of the character string STRING consisting of
  30    at most mbslen (PREFIX) characters with the character string PREFIX,
  31    ignoring case.  If the two match, return a pointer to the first byte
  32    after this prefix in STRING.  Otherwise, return NULL.
  33    Note: This function may, in multibyte locales, return non-NULL if STRING
  34    is of smaller length than PREFIX!  */
  35 char *
  36 mbspcasecmp (const char *string, const char *prefix)
  37 {
  38   /* This is essentially the same as
  39        mbsncasecmp (string, prefix, mbslen (prefix))
  40      just with small optimizations.  */
  41   if (string == prefix)
  42     return (char *) (string + strlen (string));
  43
  44   /* Be careful not to look at the entire extent of STRING or PREFIX until
  45      needed.  This is useful because when two strings differ, the difference is
  46      most often already in the very few first characters.  */
  47   if (MB_CUR_MAX > 1)
  48     {
  49       mbui_iterator_t iter1;
  50       mbui_iterator_t iter2;
  51
  52       mbui_init (iter1, string);
  53       mbui_init (iter2, prefix);
  54
  55       while (mbui_avail (iter1) && mbui_avail (iter2))
  56         {
  57           int cmp = mb_casecmp (mbui_cur (iter1), mbui_cur (iter2));
  58
  59           if (cmp != 0)
  60             return NULL;
  61
  62           mbui_advance (iter1);
  63           mbui_advance (iter2);
  64         }
  65       if (!mbui_avail (iter2))
  66         /* PREFIX equals STRING or is terminated before STRING.  */
  67         return (char *) mbui_cur_ptr (iter1);
  68       else
  69         /* STRING terminated before PREFIX.  */
  70         return NULL;
  71     }
  72   else
  73     {
  74       const unsigned char *p1 = (const unsigned char *) string;
  75       const unsigned char *p2 = (const unsigned char *) prefix;
  76       unsigned char c1, c2;
  77
  78       for (; ; p1++, p2++)
  79         {
  80           c1 = TOLOWER (*p1);
  81           c2 = TOLOWER (*p2);
  82
  83           if (c2 == '\0' || c1 != c2)
  84             break;
  85         }
  86
  87       if (c2 == '\0')
  88         /* PREFIX equals STRING or is terminated before STRING.  */
  89         return (char *) p1;
  90       else
  91         /* STRING terminated before PREFIX.  */
  92         return NULL;
  93     }
  94 }