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

[Sylvain G. V. <vi...@ii...>]

Test is: uint(y>x) << uint(z>=y) - don't know why I let all these
useless fabs in the previous email.

If largest is:
* X: 0 << ? = 0 as y<x (and we don't care about the second test)
* Y: 1 << 0 = 1 as y>x and z<y
* Z: 1 << 1 = 2 as y is replaced with z, so the tests are z>x and z>=z

From: Matt J <mjo...@gm...>
> Hmm, I fail to see how this works:
> 
> If (y > x) == 0 then that means x <= y.

!!!WRONG!!! it means that x >= y


> So,
> 
> If x <= y and z < y then 0 << 0 = 0
> If x <= y and z >= y then 0 << 1 = 0
> 
> In the first case, y is the greatest component In the second case, 
> z is the
> greatest component.
> 
> Both are encoded as 0. Something I'm missing?
> 
> 
> Hi,
> >
> > I need to compute the index (not the actual value) of the largest
> > coordinate of a normal, for some space hashing.
> >
> > I'm not sure how fast you guys usually find this index, but I've 
> just> created the following trick which I think is quite fast:
> >
> > > inline uint LargestCoordinate(const Vector3d &v)
> > > {
> > >       const float x = fabs(v.x);
> > >       const float z = fabs(v.z);
> > >       const float y = Maths::max( fabs(v.y), z );
> > >       return uint(fabs(y)>fabs(x)) << uint(fabs(z)>=fabs(y));
> > > }
> >
>