Checking if an Integer is an Exact Binary Power

[Marco Leise via Digitalmars-d]

Am Sat, 23 Apr 2016 20:34:52 +0000
schrieb Nordlöw <per.nordlow at gmail.com>:

> On Saturday, 23 April 2016 at 17:28:21 UTC, Andrei Alexandrescu 
> wrote:
> >> Yah, that's the canonical. I forgot why I chose (x & -x) > (x 
> >> - 1) over
> >> it. -- Andrei  
> 
> So is there a way to check if popcnt builtin is available on 
> current platform?

We argued in another, unrelated thread ("Any usable SIMD
implementation?") for compile-time information on the target.
That would include __traits("hasTargetFeature", "popcnt")
A runtime check requires at least a read of a global variable
and I doubt it is faster than `x & (x-1)`.

-- 
Marco