Checking if an Integer is an Exact Binary Power

[Iain Buclaw via Digitalmars-d]

On 25 April 2016 at 18:48, Lass Safin via Digitalmars-d
<digitalmars-d at puremagic.com> wrote:
> On Saturday, 23 April 2016 at 21:04:52 UTC, Nordlöw wrote:
>>
>> On Saturday, 23 April 2016 at 20:42:25 UTC, Lass Safin wrote:
>>>
>>> CPUID: https://en.wikipedia.org/wiki/CPUID.
>>> You can check for the presence of a lot of instructions with this
>>> instruction.
>>> However this will only work on x86 and only run-time.
>>
>>
>> Code you give a complete code example in D, please or point out a suitable
>> place in druntime/phobos?
>
>
> I just found this: https://dlang.org/phobos/core_cpuid.html#.hasPopcnt! It
> does exactly as it says: checks if the system has popcnt.
> Though read the top of https://dlang.org/phobos/core_cpuid.html before you
> use it:
>>
>> Bugs:
>> Currently only works on x86 and Itanium CPUs. Many processors have bugs in
>> their
>> microcode for the CPUID instruction, so sometimes the cache information
>> may be
>> incorrect.
>
>
> Example;
>
> import core.bitop;
> import core.cpuid;
>
> int count;
> if(hasPopcnt)
>     count = _popcnt; // Uses x86-instruction "popcnt".
> else
>     count = popcnt; // Phobos's software implementation.
>

version(X86)
{
  if (hasPopcnt)
    ...
}
else
{
  // API not guaranteed to be the same.
}