Compile time float binary representation

[Jeremie Pelletier]

Andrei Alexandrescu Wrote:

> Jeremie Pelletier wrote:
> > Is there a way to convert a float (or double/real) to an integral number without changing its binary representation at compile time?
> > 
> > I need to extract the sign, exponent and mantissa yet I cant use bit shifting.
> > "Error: 'R' is not of integral type, it is a real" is the error I get.
> > 
> > The usual *cast(uint*)&value wont work either at compile time.
> > 
> > Any suggestions?
> 
> I got this to work, would it be applicable to your need?
> 
> void main(string[] args)
> {
>      union A
>      {
>          double x;
>          int y;
>      }
>      enum A a = A(0.3);
>      writeln(a.x);
>      writeln(a.y);
> }
> 
> 
> Andrei

Good suggestion, however it doesnt work the way I need it:

---
template FloatParts(real R) {
    union A {
        real theReal;
        struct {
            ushort hi;
            ulong lo;
        }
    }
    
    A a = cast(A)R; // Error: cannot cast real to immutable(A)
    enum A a = A(R); // members cannot be used at runtime
}
---

I need to gather .sign, .exp and .mantissa among others (possibly a .radix too) and use them at compile time (generic metaprogramming, or else i would just fallback to runtime).

Unless there are arithmetic methods to get these, I dont see how it can be done without changes in the compiler first.

To Walter: is this something possible for DMD2.32?