gl/strncasecmp.c

   1 /* strncasecmp.c -- case insensitive string comparator
   2    Copyright (C) 1998-1999, 2005-2007, 2009-2012 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3, or (at your option)
   7    any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, see <http://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 /* Specification.  */
  20 #include <string.h>
  21
  22 #include <ctype.h>
  23 #include <limits.h>
  24
  25 #define TOLOWER(Ch) (isupper (Ch) ? tolower (Ch) : (Ch))
  26
  27 /* Compare no more than N bytes of strings S1 and S2, ignoring case,
  28    returning less than, equal to or greater than zero if S1 is
  29    lexicographically less than, equal to or greater than S2.
  30    Note: This function cannot work correctly in multibyte locales.  */
  31
  32 int
  33 strncasecmp (const char *s1, const char *s2, size_t n)
  34 {
  35   register const unsigned char *p1 = (const unsigned char *) s1;
  36   register const unsigned char *p2 = (const unsigned char *) s2;
  37   unsigned char c1, c2;
  38
  39   if (p1 == p2 || n == 0)
  40     return 0;
  41
  42   do
  43     {
  44       c1 = TOLOWER (*p1);
  45       c2 = TOLOWER (*p2);
  46
  47       if (--n == 0 || c1 == '\0')
  48         break;
  49
  50       ++p1;
  51       ++p2;
  52     }
  53   while (c1 == c2);
  54
  55   if (UCHAR_MAX <= INT_MAX)
  56     return c1 - c2;
  57   else
  58     /* On machines where 'char' and 'int' are types of the same size, the
  59        difference of two 'unsigned char' values - including the sign bit -
  60        doesn't fit in an 'int'.  */
  61     return (c1 > c2 ? 1 : c1 < c2 ? -1 : 0);
  62 }