SignedMagnitudeToTwosComplement.hpp

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#include <type_traits>

namespace duds { namespace general {

template <unsigned B, typename T>
inline typename std::make_signed<T>::type SignedMagnitudeToTwosComplement(
    const T x
) {
    // one sign bit and one magnitude bit is the minimum requirement for this
    // operation to make sense
    static_assert(
        B > 1,
        "At least 2 bits are required for signed magnitude input."
    );
    // the sign bit must be inside the integer type
    static_assert(
        B <= (sizeof(T) * 8),
        "The signed magnitude input must fit within the integer type."
    );
    struct {
        typename std::make_signed<T>::type x:B;
    } s;
    s.x = (typename std::make_signed<T>::type)x;
    if (s.x < 0) {
        s.x = (~(1 << (B - 1)) & s.x) * -1;
    }
    return s.x;
}

} }