[Mesa-dev] [PATCH] faster util_next_power_of_two() function

[Roland Scheidegger]

Am 05.06.2011 03:55, schrieb Benjamin Bellec:
> Le 05/06/2011 03:05, Matt Turner a écrit :
>> On Sat, Jun 4, 2011 at 7:14 PM, Benjamin Bellec <b.bellec at gmail.com> wrote:
>>> Le 03/06/2011 06:09, Matt Turner a écrit :
>>>> Also, if you want to check if the value is already a power-of-two,
>>>> instead of a case statement for every POT (including 0), just do the
>>>> standard is-power-of-two check:
>>>>
>>>> (x & (x - 1)) == 0
>>>
>>> My own tests (on a Core2) shows that it's less efficient to do that, at
>>> least with -O2 optimization enabled. With -O0, it's equal.
>>
>> For what input set? Powers of two?
> Both, my test case loops with 29 POT and 6 NPOT.
> I'm doing this because the OpenGL games that I have tested call the
> function more often with "good" values.
> 
>>
>> Doesn't really matter, since the function isn't a hot path or
>> anything, but I'd suppose that the Linux kernel has its
>> is_power_of_2() function for a reason--that it's pretty ugly to have
>> lots of case statements like powers of two.
>>
>> Matt
> Ok, so here is a v3 patch which replace the switch statement.

I like this one better too.
Do we actually need the x == 0 special case or would it be ok if we just
remove that (which will return 0)?

Roland