dq_rsqrt

Implements fast algorithm for approximation 1/Sqrt(x) from Quake III Arena. Useful for normalization of vectors, e.g.

uses
  dq_rsqrt;

...

  R := q_rsqrt(Sqr(X) + Sqr(Y) + Sqr(Z));
  X := X * R;
  Y := Y * R;
  Z := Z * R;