Mostly thanks to this reddit discussion, I have updated my pow() approximation for C / C++. I have now two different versions:
inline double fastPow(double a, double b) {
union {
double d;
int x[2];
} u = { a };
u.x[1] = (int)(b * (u.x[1] - 1072632447) + 1072632447);
u.x[0] = 0;
return u.d;
}


