数值的整数次方.cc

double Pow_int(double _X, int _Y)
{
	unsigned int _N;
	if (_Y >= 0)
		_N = (unsigned int)_Y;
	else
		_N = (unsigned int)(-_Y);
	for (double _Z = double(1);; _X *= _X)
	{
		if ((_N & 1) != 0)
			_Z *= _X;
		if ((_N >>= 1) == 0)
			return (_Y < 0 ? double(1) / _Z : _Z);
	}
}