Messages in this thread | | | Date | Fri, 3 Nov 2006 20:08:24 +0100 | From | Adrian Bunk <> | Subject | Re: New filesystem for Linux |
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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 <akpm@osdl.org> > > >> > > >>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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