A Fast, Compact Approximation of the Exponential Function (double precision)

fastexp.cpp

// A Fast, Compact Approximation of the Exponential Function
// http://www.schraudolph.org/pubs/Schraudolph99.pdf
inline double fast_exp(double y) {
    double d;
    *(reinterpret_cast<int*>(&d) + 0) = 0;
    *(reinterpret_cast<int*>(&d) + 1) = static_cast<int>(1512775 * y + 1072632447);
    return d;
}