https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121615
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Or just use hypot(real, imag) for integer types, which will promote them to
double that way instead.
// 26.2.7/3 abs(__z): Returns the magnitude of __z.
#if _GLIBCXX_USE_C99_COMPLEX
inline float
__complex_abs(__complex__ float __z) { return __builtin_cabsf(__z); }
inline double
__complex_abs(__complex__ double __z) { return __builtin_cabs(__z); }
inline long double
__complex_abs(const __complex__ long double& __z)
{ return __builtin_cabsl(__z); }
template<typename _Tp>
inline _Tp
abs(const complex<_Tp>& __z) { return hypot(__z.real(), __z.imag()); }
#else
template<typename _Tp>
inline
typename __gnu_cxx::__enable_if<!__is_integer<_Tp>::__value, _Tp>::__type
abs(const complex<_Tp>& __z)
{
_Tp __x = __z.real();
_Tp __y = __z.imag();
const _Tp __s = std::max(abs(__x), abs(__y));
if (__s == _Tp()) // well ...
return __s;
__x /= __s;
__y /= __s;
return __s * sqrt(__x * __x + __y * __y);
}
template<typename _Tp>
inline
typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value, _Tp>::__type
abs(const complex<_Tp>& __z) { return hypot(__z.real(), __z.imag()); }
#endif
