linux-kernel - Re: New filesystem for Linux

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Date:	Fri, 3 Nov 2006 19:14:59 +0100 (CET)
From:	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
To:	Oleg Verych <olecom@...wer.upol.cz>
Cc:	Andrew Morton <akpm@...l.org>,
	Gabriel C <nix.or.die@...glemail.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: New filesystem for Linux



On Fri, 3 Nov 2006, 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@...l.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?

The standard says that the result is undefined, so the compiler is 
standard-compliant. It could have returned any numbers and still be 
correct.

Mikulas
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