internal static extern LONG_PTR GetWindowLongPtr(
     HWND hWnd,
     GetWindowLongOffsets nIndex
 );

        // SetWindowLongPtr does not exist on x86 platforms (it's a macro that resolves to SetWindowLong).
        // We need to detect if we are on x86 or x64 at runtime and call the correct function
        // (SetWindowLongPtr on x64 or SetWindowLong on x86). Fun!
        internal static IntPtr SetWindowLong(IntPtr handle, GetWindowLongOffsets item, IntPtr newValue)
        {
            // SetWindowPos defines its error condition as an IntPtr.Zero retval and a non-0 GetLastError.
            // We need to SetLastError(0) to ensure we are not detecting on older error condition (from another function).

            IntPtr retval = IntPtr.Zero;
            SetLastError(0);

            if (IntPtr.Size == 4)
                retval = new IntPtr(SetWindowLongInternal(handle, item, newValue.ToInt32()));
            else
                retval = SetWindowLongPtrInternal(handle, item, newValue);

            if (retval == IntPtr.Zero)
            {
                int error = Marshal.GetLastWin32Error();
                if (error != 0)
                    throw new PlatformException(String.Format("Failed to modify window border. Error: {0}", error));
            }

            return retval;
        }

 private static IntPtr SetWindowLongPtr(IntPtr hWnd, GetWindowLongOffsets nIndex, IntPtr dwNewLong);

 static extern ULONG GetWindowLongInternal(HWND hWnd, GetWindowLongOffsets nIndex);

 internal static IntPtr SetWindowLong_N(IntPtr handle, GetWindowLongOffsets item, IntPtr newValue)
 {
     return IntPtr.Size == 4 ? (IntPtr)SetWindowLong(handle, item, newValue.ToInt32()) :
         SetWindowLongPtr(handle, item, newValue);
 }

 internal static IntPtr SetWindowLong(IntPtr handle, GetWindowLongOffsets item, IntPtr newValue)
 {
     IntPtr num = IntPtr.Zero;
       Functions.SetLastError(0);
       num = IntPtr.Size != 4 ? Functions.SetWindowLongPtr(handle, item, newValue) : new IntPtr(Functions.SetWindowLong(handle, item, newValue.ToInt32()));
       if (num == IntPtr.Zero)
       {
     int lastWin32Error = Marshal.GetLastWin32Error();
     if (lastWin32Error != 0)
       throw new PlatformException(string.Format("Failed to modify window border. Error: {0}", (object) lastWin32Error));
       }
       return num;
 }

 static extern LONG_PTR SetWindowLongPtrInternal(HWND hWnd, GetWindowLongOffsets nIndex,
     [MarshalAs(UnmanagedType.FunctionPtr)]WindowProcedure dwNewLong);

 static extern IntPtr SetWindowLongPtr(IntPtr hWnd, GetWindowLongOffsets nIndex, IntPtr dwNewLong);

 internal static UIntPtr GetWindowLong(IntPtr handle, GetWindowLongOffsets index)
 {
     if (IntPtr.Size == 4)
     return (UIntPtr) Functions.GetWindowLongInternal(handle, index);
       else
     return Functions.GetWindowLongPtrInternal(handle, index);
 }

 static extern int SetWindowLong(IntPtr hWnd, GetWindowLongOffsets nIndex, int dwNewLong);

 static extern UIntPtr GetWindowLongPtr(IntPtr hWnd, GetWindowLongOffsets nIndex);

 static extern uint GetWindowLong(IntPtr hWnd, GetWindowLongOffsets nIndex);

 static extern LONG SetWindowLongInternal(HWND hWnd, GetWindowLongOffsets nIndex, LONG dwNewLong);

 private static uint GetWindowLongInternal(IntPtr hWnd, GetWindowLongOffsets nIndex);

 private static UIntPtr GetWindowLongPtrInternal(IntPtr hWnd, GetWindowLongOffsets nIndex);

        internal static UIntPtr GetWindowLong(IntPtr handle, GetWindowLongOffsets index)
        {
            if (IntPtr.Size == 4)
                return (UIntPtr)GetWindowLongInternal(handle, index);

            return GetWindowLongPtrInternal(handle, index);
        }

 static extern UIntPtr GetWindowLongPtrInternal(HWND hWnd, GetWindowLongOffsets nIndex);

 internal static UIntPtr GetWindowLong_N(IntPtr handle, GetWindowLongOffsets index)
 {
     return IntPtr.Size == 4 ? (UIntPtr)GetWindowLong(handle, index) : GetWindowLongPtr(handle, index);
 }