lib/c-strcasecmp.c

   1 /* c-strcasecmp.c -- case insensitive string comparator in C locale
   2    Copyright (C) 1998-1999, 2005-2006, 2009-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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 Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 /* Specification.  */
  20 #include "c-strcase.h"
  21
  22 #include <limits.h>
  23
  24 #include "c-ctype.h"
  25
  26 int
  27 c_strcasecmp (const char *s1, const char *s2)
  28 {
  29   register const unsigned char *p1 = (const unsigned char *) s1;
  30   register const unsigned char *p2 = (const unsigned char *) s2;
  31   unsigned char c1, c2;
  32
  33   if (p1 == p2)
  34     return 0;
  35
  36   do
  37     {
  38       c1 = c_tolower (*p1);
  39       c2 = c_tolower (*p2);
  40
  41       if (c1 == '\0')
  42         break;
  43
  44       ++p1;
  45       ++p2;
  46     }
  47   while (c1 == c2);
  48
  49   if (UCHAR_MAX <= INT_MAX)
  50     return c1 - c2;
  51   else
  52     /* On machines where 'char' and 'int' are types of the same size, the
  53        difference of two 'unsigned char' values - including the sign bit -
  54        doesn't fit in an 'int'.  */
  55     return _GL_CMP (c1, c2);
  56 }