On 02/23/2015 06:59 AM, Markus Armbruster wrote: > Alexey Kardashevskiy <a...@ozlabs.ru> writes: > >> This adds a helper to get closest bigger power-of-two value. >>
>
> Here's how I'd do these functions:
>
> int64_t pow2floor(int64_t value)
> {
> assert(value > 0);
> return 0x8000000000000000u >> clz64(value);
> }
Needs to be 0x8000000000000000ull for 32-bit machines to compile correctly.
Why is the parameter int64_t? Wouldn't it be more useful to have:
uint64_t pow2floor(uint64_t value)
>
> int64_t pow2ceil(int64_t value)
> {
Again, why allow signed inputs?
> assert(value <= 0x4000000000000000)
> if (value <= 1)
> return 1;
In particular, this slams all negative values to a result of 1, which
doesn't necessarily make sense.
> return 0x8000000000000000u >> (clz64(value - 1) - 1);
> }
>
>
>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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