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SubjectRe: 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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