Inverse Square Root

Hello-

I was wondering if it is possible to include the quake fast inverse square
root function in ruby?  I think all you would have to do is add the
following method to math.c

/*
 *  call-seq:
 *     Math.isqrt(numeric)    => float
 *
 *  Returns the inverse square root of <i>numeric</i>.
 */
static VALUE
math_isqrt(obj, y)
    VALUE obj, y;
{
    float x;

    Need_Float(y);
    x = (float) RFLOAT(y)->value;
    float xhalf = 0.5f*x;
    int i = *(int*)&x;
    i = 0x5f3759df - (i >> 1);
    x = *(float*)&i;
    x = x*(1.5f - xhalf*x*x);
    return rb_float_new(x);
}

Then, further down, add the following:

    rb_define_module_function(rb_mMath, "isqrt", math_isqrt, 1);


I added the code to my local source copy of 1.8.6 then ran make and make
install.  Finally, I ran the following ruby script:

#!/usr/bin/ruby -w
for i in 0..20
  print i
  print " - "
  puts Math.isqrt(i)
end

Which gave the following results (which seem correct):

0 - 1.98177537096858e+19
1 - 0.998307168483734
2 - 0.706930041313171
3 - 0.576846837997437
4 - 0.499153584241867
5 - 0.447141021490097
6 - 0.407681375741959
7 - 0.377444177865982
8 - 0.353465020656586
9 - 0.332953214645386
10 - 0.315685778856277
11 - 0.301036149263382
12 - 0.288423418998718
13 - 0.277312487363815
14 - 0.267214089632034
15 - 0.25775083899498
16 - 0.249576792120934
17 - 0.242388844490051
18 - 0.235677853226662
19 - 0.229414582252502
20 - 0.223570510745049

Cheers,

-Dave