Re: egcs, warning patch for missing initializers in xsys-protos.h

["Kaveh R. Ghazi" <ghazi at caip dot rutgers dot edu>]

 > From: Richard Henderson <rth@cygnus.com>
 > 
 > On Sat, Sep 19, 1998 at 09:01:55AM -0400, Kaveh R. Ghazi wrote:
 > > 	IMHO, you can't safely cast ctype function arguments in the
 > > ctype macros.  This was partially discussed last February starting with:
 > > http://www.cygnus.com/ml/egcs/1998-Feb/0643.html.  It became clear, in
 > > that discussion, that casting to int was bad.
 > 
 > What I see in that thread are a lot of what-ifs.  I ask those
 > involved the last time round: are there any actual systems that
 > display actual problems?


	Yes, see below.



 > 
 > > The warning is pointing
 > > out something valid, the fact that char is often signed and when you
 > > evaluate character values > 127, you get negative results.  Ctype macros
 > > are often defined as lookups in an array, thus the negative index is
 > > bogus. 
 > 
 > Not necessarily.  For instance glibc defines things like this
 > 
 > 	static unsigned short ctype_b[128+256] = {...}
 > 	unsigned short *__ctype_b = &ctype_b[128];
 > 
 > which means that negative values do work.  Do actual implementations
 > really get this wrong?  Virtually all systems define EOF as -1 and
 > so must do something like this anyway.
 > r~



	I believe linux is the exception here.  I wrote a small
program to test this.  (Feel free to point out to me if the test
program is bogus, if it is in fact so.)



 > #include <stdio.h>
 > #include <ctype.h>
 > 
 > int main()
 > {
 >   int i;
 >   signed char sc;
 >   unsigned char uc;
 >   
 >   for (i=128; i<256; i++)
 >     {
 >       sc = uc = i;
 >       if (isalpha(sc) != isalpha(uc))
 > 	printf("(isalpha(%c)[%d]=%d) != (isalpha(%c)[%d]=%d)\n",
 > 	       sc, sc, isalpha(sc), uc, uc, isalpha(uc));
 >     }
 > 
 >   return 0;
 > }

	If signed vs unsigned chars passed to ctype functions doesn't
matter, then the program should produce no output.  Here are the
actual results.

sparc-sun-sunos4.1.4			FAILED
sparc-sun-solaris2.5			FAILED
alphaev5-dec-osf4.0b			FAILED
powerpc-ibm-aix4.1.4.0			PASS
mips-sgi-irix4.0.5			core dumped
mips-sgi-irix6.2			FAILED
sparc-unknown-linux-gnulibc1		PASS

	As you can see, most of the platforms failed.

		--Kaveh
--
Kaveh R. Ghazi			Engagement Manager / Project Services
ghazi@caip.rutgers.edu		Icon CMT Corp.