lib/strncasecmp_l.c

/* Case-insensitive string comparison function for unibyte locales.
   Copyright (C) 1998-2026 Free Software Foundation, Inc.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   This file is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */
#include <strings.h>

#include <ctype.h>
#include <limits.h>
#include <string.h>

#include "c-strcase.h"

int
strncasecmp_l (const char *s1, const char *s2, size_t n, locale_t locale)
{
#if GNULIB_defined_locale_t

  struct gl_locale_category_t *plc =
    &locale->category[gl_log2_lcmask_to_index (gl_log2_lc_mask (LC_CTYPE))];
  if (plc->is_c_locale)
    /* Implementation for the "C" locale.  */
    return c_strncasecmp (s1, s2, n);
# if HAVE_WINDOWS_LOCALE_T
  /* Documentation:
     <https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/strnicmp-wcsnicmp-mbsnicmp-strnicmp-l-wcsnicmp-l-mbsnicmp-l>  */
  return _strnicmp_l (s1, s2, n, plc->system_locale);
# else
  /* Implementation for the global locale.  */
  {
#  if HAVE_WORKING_USELOCALE
    locale_t saved_locale = uselocale (LC_GLOBAL_LOCALE);
#  endif
    int ret = strncasecmp (s1, s2, n);
#  if HAVE_WORKING_USELOCALE
    uselocale (saved_locale);
#  endif
    return ret;
  }
# endif

#else

  if (s1 == s2 || n == 0)
    return 0;

  for (;; s1++, s2++)
    {
      unsigned char c1 = tolower_l ((unsigned char) *s1, locale);
      unsigned char c2 = tolower_l ((unsigned char) *s2, locale);

      if (--n == 0 || c1 == '\0' || c1 != c2)
        {
          if (UCHAR_MAX <= INT_MAX)
            return c1 - c2;
          else
            /* On machines where 'char' and 'int' are types of the same size,
               the difference of two 'unsigned char' values - including the
               sign bit - doesn't fit in an 'int'.  */
            return _GL_CMP (c1, c2);
        }
    }

#endif
}