[sldev] getting serious about software.

[Callum Lerwick]

On Sat, 2007-06-23 at 15:28 +0200, Nicholaz Beresford wrote:
> Just for the fun of it, here's my version
> (it's exactly the same behavior as the float
> version, not rounding up numbers that are already
> powers of two).

> +S32 next_power_of_two(S32 n)
> +{
> +	S32 res = (n<(1<<15)) ? (1<<15) : (1<<30);
> +
> +	while (res>=n) {
> +		res>>= 1;
> +	}
> +
> +	return (res<<1);
> +}

This is a little over twice as fast on my Athlon 64, about a third
faster on my PIII, and a quarter faster on my G3 iMac:

int next_power_of_two2(int v){
   v--;
   v |= v >> 1;
   v |= v >> 2;
   v |= v >> 4;
   v |= v >> 8;
   v |= v >> 16;
   v++;

   return v;
}

(Snagged from here:
http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2Float )

At any rate, the existing version is reeeally slow. Please Jira this.
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