Mine

    public struct FloorTile
    {
        public byte Prop1;
        public byte Prop2;
        public byte Prop3;
        public byte Prop4;

        public uint Orientation
        {
            get
            {
                return 0;
            }
        }
        public uint SubIndex
        {
            get
            {
                if(this.Prop1 == 1)
                    return this.Prop2;

                return 0;
            }
        }
        public uint MainIndex
        {
            get
            {
                if (this.Prop1 == 1)
                    return ((uint)this.Prop3 / 16) + (((uint)this.Prop4 & 0x0F) * 16);

                return 0;
            }
        }
    }