Re: Quick inverse square root

[AdaMagica <christ-usch.grein@t-online.de>]

> with INTERFACES; use INTERFACES;
> generic 
> type F is digits <>; 
> type U is mod <>;
> with function SHIFT_RIGHT( n : U; amount : NATURAL ) return U; 
> function G_QUICK_INVERSE_SQRT( a : F ) return F; 
> 
> function G_QUICK_INVERSE_SQRT( a : F ) return F is 

  pragma Assert (F'Base'Size = U'Modulus);

> magic : constant U := U(1.5 * 2.0**(F'Machine_Mantissa - 1) * (F(F'Machine_Emax - 1) - 0.043));
> y : F := a; 
> i : U; 
> for i'Address use y'Address; 
> begin 
> i := magic - shift_right( i, 1 ); 
> return y * (1.5 - (0.5 * a * y * y));
> end G_QUICK_INVERSE_SQRT;