Re: [Bug c/37609] New: Pointer arithmetic yields strange result

[Andrew Thomas Pinski <pinskia at gmail dot com>]

Sent from my iPhone

On Sep 21, 2008, at 9:00 AM, "john dot spelis at 3dlabs dot com" <gcc-bugzilla@gcc.gnu.org 
> wrote:

> An expression using ptr arithmetic yields an unusual result
> unless a cast is applied;
> The problematic expression;
> MaxTimings = ((EDIDDetailed *) &pExt->checksum) - pDTD;

That is a signed division while the below is unsigned.

> works only when cast as;
> MaxTimings = (((uintptr_t) &pExt->checksum) - ((uintptr_t)
> pDTD))/sizeof(*pDTD);
>
> This occurs on compilers back to 3.0.3 when testing on a x86. It's  
> also present
> in a cross compiler built using 4.3.0 source
> Works on a Sun/Solaris compiler.
> A test program is attached
>
>
> --
>           Summary: Pointer arithmetic yields strange result
>           Product: gcc
>           Version: 4.3.0
>            Status: UNCONFIRMED
>          Severity: normal
>          Priority: P3
>         Component: c
>        AssignedTo: unassigned at gcc dot gnu dot org
>        ReportedBy: john dot spelis at 3dlabs dot com
> GCC build triplet: i686-pc-linux-gnu
>  GCC host triplet: i686-pc-linux-gnu
> GCC target triplet: i686-pc-linux-gnu
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37609