D equivalent of C++ reinterpret cast?

[Steven Schveighoffer]

On Sun, 19 Sep 2010 13:39:38 -0400, Bradley Mitchell  
<abstractant1 at gmail.com> wrote:

> Hello,
>
> I'm trying to implement the Quake 3 fast inverse square root algorithm  
> which
> requires casting from int to float without modifying the stored bits. A  
> C++
> reinterpret cast seems to accomplish this just fine but so far I have  
> had no
> success in D after trying quite a few different things. Here is the C++  
> I've
> written that currently works:
>
> #include <iostream>
>
> float fastInvSqrt( float x )
> {
>     const int INV_SQRT_N = 1597292357;
>     const float MULT = 1.000363245811462f;
>
>     float const mx = 0.5f * MULT * x;
>     int xi = *reinterpret_cast<int *>( &x );

Note the use of pointers and address above?

>     xi = INV_SQRT_N - (xi >> 1);
>     x = *reinterpret_cast<float *>( &xi );
>     return x * (1.5f * MULT - mx * x * x);
> }
>
> int main()
> {
>     float a = fastInvSqrt( 9.0f );
>     std::cout << a << std::endl;
> }
>
> And here is my D code that doesn't work yet:
>
> module test;
>
> import std.stdio;
>
> float fastInvSqrt( float x )
> {
>     const int INV_SQRT_N = 1597292357;
>     const float MULT = 1.000363245811462f;
>
>     float mx = 0.5f * MULT * x;
>     int xi = cast(int)cast(void*)x;

You forgot that here...

int xi = *cast(int *)(&x);

rule of thumb -- if you want to do a reinterpret cast, you usually must  
take the address first.  The compiler never tries anything tricky on  
pointer casts.

-Steve