From: Johan Råde (rade_at_[hidden])
Date: 2006-08-02 11:24:14
Paul A Bristow wrote:
> Does anyone have a ***portable*** version of macro signbit (C99)
>
> or can we combine versions that work on each compiler/hardware/endian...
>
> or an equivalent C++ function, perhaps called is_negative?
>
> (This would just test the signbit for the type(s)).
>
> There are several places where this would be useful in dealing properly with
> NaNs and zero and infinity etc.
Or how about this
template<class T>
bool is_negative(const T& x)
{
return x < T(0);
}
template<>
bool is_negative(const float& x)
{
const float one = 1;
const float neg_one = -1;
const int one_bits = reinterpret_cast<const int&>(one);
const int neg_one_bits = reinterpret_cast<const int&>(neg_one);
const int sign_mask = one_bits ^ neg_one_bits;
return reinterpret_cast<const int&>(x) & sign_mask;
}
template<>
bool is_negative(const double& x)
{
return is_negative(static_cast<float>(x));
}
template<>
bool is_negative(const long double& x)
{
return is_negative(static_cast<float>(x));
}
--Johan Råde