/// @returns the 64-bit value of this constant if its active bits number is
/// not greater than 64, otherwise, just return the given uint64_t number.
/// @brief Get the constant's value if possible.
/// @returns the 64-bit value of this constant if its active bits number is
/// not greater than 64, otherwise, just return the given uint64_t number.
/// @brief Get the constant's value if possible.