From Newsgroup: comp.lang.c++

Similar to nextafter, but much faster:

template<typename Fp>
template<bool Up>
constexpr Fp fp_tools<Fp>::next( Fp v ) noexcept
{
using namespace std;
constexpr Fp Min = numeric_limits<Fp>::denorm_min();
sword sBin = bit_cast<word>( v );
word uBin = sBin & ~Sign;
if( !uBin ) [[unlikely]]
return Up ? Min : -Min;
sword mxDiff = uBin - Exp;
if( mxDiff > 0 ) [[unlikely]]
return v;
bool toInf = Up ? sBin >= 0 : sBin < 0;
if( !mxDiff && toInf ) [[unlikely]]
return v;
sBin += toInf ? 1 : -1;
word exp = sBin & Exp;
if( exp == Exp || !exp ) [[unlikely]]
{
feraiseexcept( FE_INEXACT | (exp == Exp ? FE_OVERFLOW : FE_UNDERFLOW) );
errno = ERANGE;
return v;
}
return bit_cast<Fp>( sBin );
}
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