1  /* Case-insensitive string comparison function.
       2     Copyright (C) 1998-1999, 2005-2007, 2009-2023 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  #define TOLOWER(Ch) (isupper (Ch) ? tolower (Ch) : (Ch))
      26  
      27  /* Compare strings S1 and S2, ignoring case, returning less than, equal to or
      28     greater than zero if S1 is lexicographically less than, equal to or greater
      29     than S2.
      30     Note: This function does not work with multibyte strings!  */
      31  
      32  int
      33  strcasecmp (const char *s1, const char *s2)
      34  {
      35    const unsigned char *p1 = (const unsigned char *) s1;
      36    const unsigned char *p2 = (const unsigned char *) s2;
      37    unsigned char c1, c2;
      38  
      39    if (p1 == p2)
      40      return 0;
      41  
      42    do
      43      {
      44        c1 = TOLOWER (*p1);
      45        c2 = TOLOWER (*p2);
      46  
      47        if (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 _GL_CMP (c1, c2);
      62  }