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Re: 20040309-1.c vs overflow being undefined
- From: Falk Hueffner <falk at debian dot org>
- To: Andrew Pinski <pinskia at physics dot uc dot edu>
- Cc: gcc at gcc dot gnu dot org
- Date: Sun, 27 Nov 2005 18:18:02 +0100
- Subject: Re: 20040309-1.c vs overflow being undefined
- References: <200511271702.jARH2lb2016784@earth.phy.uc.edu>
Andrew Pinski <pinskia@physics.uc.edu> writes:
> If we look at this testcase, we have a function like:
> int foo(unsigned short x)
> {
> unsigned short y;
> y = x > 32767 ? x - 32768 : 0;
> return y;
> }
>
>
> x is promoted to a signed int by the front-end as the type
> of 32768 is signed. So when we pass 65535 to foo (like in the testcase),
> we get some large negative number for (signed int)x
That shouldn't happen. Promoting from unsigned short to int shouldn't
sign extend. If you see it happening, then that's a bug.
> Should the testcase have -fwrapv or change 32768 to 32768u?
I don't see any reason to.
--
Falk