0 is not a power of 2

[Zoadian via Digitalmars-d]

On Tuesday, 19 May 2015 at 18:04:49 UTC, Marco Leise wrote:
> Am Mon, 18 May 2015 22:16:47 -0700
> schrieb Andrei Alexandrescu <SeeWebsiteForEmail at erdani.org>:
>
>> But that has branches in it. So I came up with:
>> 
>> bool isPowerOf2(uint x)
>> {
>>      return (x & (x - 1) | !x) == 0;
>> }
>> 
>> which has no branches at least with dmd, see 
>> http://goo.gl/TVkCwc.
>> 
>> Any ideas for faster code?
>> 
>> 
>> Thanks,
>> 
>> Andrei
>
> Any faster ?! This is already minimal assembly code with
> pretty looks!
>
> While you are at it, you might also need "round pointer up to"
> and "round pointer down to", which can be implemented with bit
> ops for power-of-2 multiples.
>
> Its the kind of stuff that's not really a std.algorithm
> candidate, but still somewhat common in memory management code.
> Often these and other little helpers end up in everyones
> stdlib_extensions.d which I suppose don't look all that
> different. Who has some of these in their code?:
>
> - isPowerOf2, nextLargerPowerOf2
> - roundUp/Down to multiple of X
> - increment with wraparound at X
> - clamp value (low, high or both ends)
> - check if numerical value is in between two others
> - compile time "iota"
> - format an argument as it would appear in source code
>   (i.e. add quotes around strings)

+1 ;)
all except the last one