Re: new module 'c-strcase'

[Bruno Haible]

Paul Eggert wrote:
> > More precisely, one of the string arguments must be an ASCII string;
> > the other one can also contain non-ASCII characters (but then the
> > comparison result will be nonzero).
>
> Why is this restriction needed?

It is needed to guarantee that the result is equivalent to the comparison
result in the C locale. On a system where the C locale has UTF-8 encoding,

  c_strcasecmp ("François", "FRANÇOIS") != 0

although

  setlocale (LC_ALL, "C");
  strcasecmp ("François", "FRANÇOIS") == 0.

> Doesn't the code simply
> compare bytes after converting 'A'-'Z' to 'a'-'z'?  In that case,
> it is not really required that one argument must be an ASCII string;
> both strings can be non-ASCII but the result is still well-defined.

The result is then well-defined but not related to the behaviour of
the C locale on such systems, and the name of the module would be a
misnomer :-)

> >   return c1 - c2;
>
> A nit: in theory this could result in integer overflow.
> The following would be portable to machines where char == int.
>
>    return UCHAR_MAX <= INT_MAX ? c1 - c2 : c1 < c2 ? -1 : c1 > c2;
>
> Such machines do exist.  They are unlikely targets for big GNU
> apps but are potential targets for this module.

OK, fixed. But just for info, what are these machines? The 10-year old
CRAY ?

Bruno


2005-10-11  Bruno Haible  <address@hidden>

        * strcasecmp.c: Include limits.h.
        (strcasecmp): Avoid integer overflow on exotic platforms.
        * strncasecmp.c: Include limits.h.
        (strncasecmp): Avoid integer overflow on exotic platforms.
        Reported by Paul Eggert.

diff -c -3 -r1.10 strcasecmp.c
*** strcasecmp.c        17 Aug 2005 14:01:07 -0000      1.10
--- strcasecmp.c        11 Oct 2005 12:47:19 -0000
***************
*** 25,30 ****
--- 25,31 ----
  #include "strcase.h"
  
  #include <ctype.h>
+ #include <limits.h>
  
  #if HAVE_MBRTOWC
  # include "mbuiter.h"
***************
*** 93,98 ****
        }
        while (c1 == c2);
  
!       return c1 - c2;
      }
  }
--- 94,105 ----
        }
        while (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 (c1 > c2 ? 1 : c1 < c2 ? -1 : 0);
      }
  }
diff -c -3 -r1.6 strncasecmp.c
*** strncasecmp.c       19 Sep 2005 17:28:15 -0000      1.6
--- strncasecmp.c       11 Oct 2005 12:47:19 -0000
***************
*** 1,5 ****
  /* strncasecmp.c -- case insensitive string comparator
!    Copyright (C) 1998, 1999 Free Software Foundation, Inc.
  
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
--- 1,5 ----
  /* strncasecmp.c -- case insensitive string comparator
!    Copyright (C) 1998, 1999, 2005 Free Software Foundation, Inc.
  
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
***************
*** 23,28 ****
--- 23,29 ----
  #include "strcase.h"
  
  #include <ctype.h>
+ #include <limits.h>
  
  #define TOLOWER(Ch) (isupper (Ch) ? tolower (Ch) : (Ch))
  
***************
*** 54,58 ****
      }
    while (c1 == c2);
  
!   return c1 - c2;
  }
--- 55,65 ----
      }
    while (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 (c1 > c2 ? 1 : c1 < c2 ? -1 : 0);
  }