How to get the bits of a “double” as a “long”

Question

I would like to manipulate the bitwise representation of floating-point numbers in C#. BinaryWriter and BinaryReader do it this way:

public virtual unsafe void W         


        

Answer 1

Another way is to use a custom struct with explicit layout that defines both a long and a double at offset 0. This is equivalent to a union in C.

Something like this:

using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Explicit)]
struct DoubleLongUnion
{
    [FieldOffset(0)] 
    public long Long;
    [FieldOffset(0)] 
    public double Double;
}

Then use this:

var union = new DoubleLongUnion();
union.Double = 1.234d;
var longBytes = union.Long;

This will avoid any unsafe code and should perform pretty fast too as you perform the conversion on the stack.

I haven't tried/compiled this but I reckon it should work :)

EDIT

I just tried this and it works. The value of longBytes above is 4608236261112822104.

Some other values:

0d              -> 0L
double.NaN      -> -2251799813685248L
double.MinValue -> -4503599627370497L
double.MaxValue -> 9218868437227405311L

Here's a method that does what you want:

public static long DoubleToLong(double d)
{
    return new DoubleLongUnion { Double = d }.Long;
}