Bug in strncasecmp routine (glib source)

[Tor Lillqvist <tml iki fi>]

Forwarded from gimpwin-users:

From: Jean-Louis HAMEL <jlhamel@club-internet.fr>
To: gimpwin-users@egroups.com
Subject: [gimpwin-users] Bug in strncasecmp routine (glib source)
Date: Wed, 05 Jul 2000 21:54:31 +0200

Hi,

I have found a bug in the routine "strncasecmp()" which stays in the
file "gstrfuncs.c" from the glib stuff. It affects the Windows version
and some Unix lacking of a native version of this routine.

Here is a part of this routine:

  while (n-- && *s1 && *s2)
    {
      /* According to A. Cox, some platforms have islower's that
       * don't work right on non-uppercase
       */
      c1 = isupper ((guchar)*s1) ? tolower ((guchar)*s1) : *s1;
      c2 = isupper ((guchar)*s2) ? tolower ((guchar)*s2) : *s2;
      if (c1 != c2)
	return (c1 - c2);
      s1++; s2++;
    }
  if (n) /* <============= WRONG, should be if(++n) */
    return (((gint)(guchar) *s1) - ((gint)(guchar) *s2));
  else
    return 0;

If the while loop exits on n = 0, n is postdecremented and takes the -1
value, and the test "if (n)" does not not work correctly, leading to a
wrong result. As an example:
	strncasecmp("AB", "ABC", 2)
gives a non null result.

Correction: replace "if(n)" by "if(++n)".

The correction should be applied soon, since this bug produces errors
difficult to find...

I have found this bug when, after having successfully compiled the
guash-2.2.3 plugin (from the TML's source snapshot), I tried to
understand why this guash version attempted always to rebuild all the
thumbnails, even when they already existed. Looking at the program
source, I found that this behavior came from a wrong result of an
strncasecmp() call.

					JLH