Re: [PATCH] Add "is_power_of_2" checking to log2.h.

On Thu, 1 Feb 2007, [email protected] wrote:

> On Thu, 01 Feb 2007 13:39:15 +0100, Tim Schmielau said:
> > #define is_power_of_4(x) (is_power_of_2_or_zero(x) \
> >                           && (x & ((typeof(x))0x55555555)))
> 
> Those 5's are going to need more magic if x is a 64-bit typeof?

Yeah, I can't count. Make that

#define is_power_of_2_or_zero(x) ((x & (x-1))==0)
#define is_power_of_4(x) (is_power_of_2_or_zero(x) \
                          && (x & ((typeof(x))0x5555555555555555ull)))

of course.

Thanks,
Tim
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References:
- [PATCH] Add "is_power_of_2" checking to log2.h.
  - From: "Robert P. J. Day" <[email protected]>
- Re: [PATCH] Add "is_power_of_2" checking to log2.h.
  - From: David Howells <[email protected]>
- Re: [PATCH] Add "is_power_of_2" checking to log2.h.
  - From: Tim Schmielau <[email protected]>
- Re: [PATCH] Add "is_power_of_2" checking to log2.h.
  - From: [email protected]

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