Re: Inverse Square Root

Yes they are.  I remembered (after the fact) that it is an approximation
algorithm and probably doesn't make sense to include in Ruby.  To get more
accurate results you would have to run the following line a couple times:

x = x*(1.5f - xhalf*x*x);

But still...the results will be incorrect or rough.  It is actually slower
too (at least the way I coded it):

When calculating the inverse square root with my Math.isqrt(), the value was
0.999995648860931 and it took  4.0E-6 seconds
When calculating the inverse square root with 1.0/Math.sqrt(), the value was
1.0 and it took  3.0E-6 seconds

I guess the fast inverse square root would only make sense to include iff
someone needed an approximation that didn't rely on division.

Thanks,

-Dave

On 8/24/07, Nobuyoshi Nakada <[e-mail]> wrote:
>
> Hi,
>
> At Fri, 24 Aug 2007 15:28:26 +0900,
> Dave Pederson wrote in [ruby-core:11981]:
> > Which gave the following results (which seem correct):
> >
> > 1 - 0.998307168483734
> > 4 - 0.499153584241867
> > 9 - 0.332953214645386
> > 16 - 0.249576792120934
>
> Seem incorrect or quite rough.
>
> --
> Nobu Nakada
>
>