lib/strncasecmp.c

   1 /* strncasecmp.c -- case insensitive string comparator
   2    Copyright (C) 1998-1999, 2005-2007, 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 <string.h>
  21
  22 #include <ctype.h>
  23 #include <limits.h>
  24
  25 /* Compare no more than N bytes of strings S1 and S2, ignoring case,
  26    returning less than, equal to or greater than zero if S1 is
  27    lexicographically less than, equal to or greater than S2.
  28    Note: This function cannot work correctly in multibyte locales.  */
  29
  30 int
  31 strncasecmp (const char *s1, const char *s2, size_t n)
  32 {
  33   register const unsigned char *p1 = (const unsigned char *) s1;
  34   register const unsigned char *p2 = (const unsigned char *) s2;
  35   unsigned char c1, c2;
  36
  37   if (p1 == p2 || n == 0)
  38     return 0;
  39
  40   do
  41     {
  42       c1 = tolower (*p1);
  43       c2 = tolower (*p2);
  44
  45       if (--n == 0 || c1 == '\0')
  46         break;
  47
  48       ++p1;
  49       ++p2;
  50     }
  51   while (c1 == c2);
  52
  53   if (UCHAR_MAX <= INT_MAX)
  54     return c1 - c2;
  55   else
  56     /* On machines where 'char' and 'int' are types of the same size, the
  57        difference of two 'unsigned char' values - including the sign bit -
  58        doesn't fit in an 'int'.  */
  59     return _GL_CMP (c1, c2);
  60 }