HandleMap.cs

public class HandleMap
{
    // Map between environments
    public IntPtr To32(ushort handle16)
    public ushort To16(IntPtr handle32)

    // Remove destroyed handles
    public void Destroy32(IntPtr handle32);
    public void Destroy16(ushort handle16);
    
    // Check if a handle is known
    public bool IsValid16(ushort handle16)

    // The map
    Dictionary<IntPtr, ushort> _map32to16 = new Dictionary<IntPtr, ushort>();
    Dictionary<ushort, IntPtr> _map16to32 = new Dictionary<ushort, IntPtr>();
    
    // Next unused handle
    ushort _nextHandle = 32;
}