On Fri, Nov 03, 2006 at 06:36:09PM +0100, Oleg Verych wrote:
> On Fri, Nov 03, 2006 at 06:09:39PM +0100, Mikulas Patocka wrote:
> > >In gmane.linux.kernel, you wrote:
> > >[]
> > >>From: Andrew Morton <[email protected]>
> > >>
> > >>As Mikulas points out, (1 << anything) won't be evaluating to zero.
> > >
> > >How about integer overflow ?
> >
> > C standard defines that shifts by more bits than size of a type are
> > undefined (in fact 1<<32 produces 1 on i386, because processor uses only 5
> > bits of a count).
> ,--
> |#include <stdio.h>
> |int main(void) {
> | unsigned int b = 1;
> |
> | printf("%u\n", (1 << 33));
> | printf("%u\n", (b << 33));
> | return 0;
> |}
> |$ gcc bit.c && ./a.out
> `--
>
> There *is* difference, isn't it?
It's undefined, and the results with your example depend on the gcc
version and optimization level.
E.g. with gcc 4.1, there is *no* difference any more if you turn on
optimization.
cu
Adrian
--
"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed
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