// reverse byte order (16-bit)
public static UInt16 ReverseBytes(UInt16 value)
{
  return (UInt16)((value & 0xFFU) << 8 | (value & 0xFF00U) >> 8);
}

// reverse byte order (32-bit)
public static UInt32 ReverseBytes(UInt32 value)
{
  return (value & 0x000000FFU) << 24 | (value & 0x0000FF00U) << 8 |
         (value & 0x00FF0000U) >> 8 | (value & 0xFF000000U) >> 24;
}

// reverse byte order (64-bit)
public static UInt64 ReverseBytes(UInt64 value)
{
  return (value & 0x00000000000000FFUL) << 56 | (value & 0x000000000000FF00UL) << 40 |
         (value & 0x0000000000FF0000UL) << 24 | (value & 0x00000000FF000000UL) << 8 |
         (value & 0x000000FF00000000UL) >> 8 | (value & 0x0000FF0000000000UL) >> 24 |
         (value & 0x00FF000000000000UL) >> 40 | (value & 0xFF00000000000000UL) >> 56;
}