Re: [Algorithms] How to get 3dvector largest coordinate index?

[Jon W. <jw...@gm...>]

Sylvain G. Vignaud wrote:
> I didn't need such function before, so I'm not sure if this is
> considered fast or slow. Do you guys have something faster?
>   

What hardware are you running on? Does it have conditional moves? Is it 
in-order or out-of-order? Does it have memory pre-fetch?

In general, I would guess that there just won't be a measurable 
difference compared to the time spent waiting for the normal to arrive 
out of DRAM.
My code to do the same thing does:

  float x = fabsf(n.x);
  float y = fabsf(n.y);
  float z = fabsf(n.z);
  return (x > y) ? (x > z) ? 0 : 2 : (y > z) ? 1 : 2;

I've never found this to show up in any profile, and on x86, I believe a 
competent compiler generates cmov.
I guess you could even do it with ints where you mask away the top bit, 
if I knew that type aliasing wouldn't kill me.

Sincerely,

jw