Question

I have a project that I am working on where I require a data type that doesn’t exist in the .NET BCL – an Unsigned Int24. For calculations that I am doing, the 4th byte in an int32, even when set to all zeroes, screws up my results.

EDIT:
I’m doing bitwise circular shifts on a 24bit integer space that is limited to only 24bits. If the rotation is performed at 24bit level on a 32bit number the result is wildly incorrect.

Does anyone know of any third party implementations of this data type that are available?

Thanks!

Answer 1

Implementing Int24 isn’t hard (honest!). But we need to know more about why you need to implement it. @nneonneo wonders if you’re trying to interface with a native library that uses 24-bit integers. If that’s the case then you can be done by doing something like this:

[StructLayout(LayoutKind.Sequential)]
public struct UInt24 {
    private Byte _b0;
    private Byte _b1;
    private Byte _b2;

    public UInt24(UInt32 value) {
        _b0 = (byte)( (value      ) & 0xFF );
        _b1 = (byte)( (value >>  8) & 0xFF ); 
        _b2 = (byte)( (value >> 16) & 0xFF );
    }

    public unsafe Byte* Byte0 { get { return &_b0; } }

    public UInt32 Value { get { return _b0 | ( _b1 << 8 ) | ( _b2 << 16 ); } }
}

// Usage:

[DllImport("foo.dll")]
public static unsafe void SomeImportedFunction(byte* uint24Value);

UInt24 uint24 = new UInt24( 123 );
SomeImportedFunction( uint24.Byte0 );

Modifying the class for big-endian or signed Int24 is an exercise left up to the reader.