linux-kernel - Re: Problems (a bug?) with UINT

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Message-ID: <4665AD01.6030003@zytor.com>
Date:	Tue, 05 Jun 2007 11:35:45 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Richard Purdie <richard@...nedhand.com>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problems (a bug?) with UINT_MAX from kernel.h

Richard Purdie wrote:
> The kernel uses UINT_MAX defined from kernel.h in a variety of places.
> 
> While looking at the behaviour of the LZO code, I noticed it seemed to
> think an int was 8 bytes large on my 32 bit i386 machine. It isn't but
> why did it think that?
> 
> kernel.h says:
> 
> #define INT_MAX		((int)(~0U>>1))
> #define INT_MIN		(-INT_MAX - 1)
> #define UINT_MAX	(~0U)
> #define LONG_MAX	((long)(~0UL>>1))
> #define LONG_MIN	(-LONG_MAX - 1)
> #define ULONG_MAX	(~0UL)
> #define LLONG_MAX	((long long)(~0ULL>>1))
> #define LLONG_MIN	(-LLONG_MAX - 1)
> #define ULLONG_MAX	(~0ULL)
> 
> If I try to compile the code fragment below, I see the error:
> 
> #define UINT_MAX	(~0U)
> #if (0xffffffffffffffff == UINT_MAX)
>   #error argh
> #endif
> 
> I've tested this on several systems with a variety of gcc versions with
> the same result. I've tried various other ways of testing this all with
> the same conclusion, UINT_MAX is wrong.
> 

C99 states that all arithmetic in the preprocessor is done in
(u)intmax_t, regardless of prefixes or suffixes.

	-hpa
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