e的快速幂算法

#include 


double exp_double(double y)
{
	double d = 0.0;
	*((int*)(&d) + 0) = 0;
	*((int*)(&d) + 1) = (int)(1512775 * y + 1072632447);
	return d;
}


static float exp_coef[10][16] = {
 { 1.0f, 1.00024f, 1.00049f, 1.00073f, 1.00098f, 1.00122f, 1.00147f, 1.00171f, 1.00196f, 1.0022f, 1.00244f, 1.00269f, 1.00293f, 1.00318f, 1.00342f, 1.00367f },
 { 1.0f, 1.00391f, 1.00784f, 1.01179f, 1.01575f, 1.01972f, 1.02371f, 1.02772f, 1.03174f, 1.03578f, 1.03984f, 1.04391f, 1.04799f, 1.05209f, 1.05621f, 1.06034f },
 { 1.0f, 1.06449f, 1.13315f, 1.20623f, 1.28403f, 1.36684f, 1.45499f, 1.54883f, 1.64872f, 1.75505f, 1.86825f, 1.98874f, 2.117f, 2.25353f, 2.39888f, 2.55359f },
 { 1.0f, 2.71828f, 7.38906f, 20.0855f, 54.5981f, 148.413f, 403.429f, 1096.63f, 2980.96f, 8103.08f, 22026.5f, 59874.1f, 162755.0f, 442413.0f, 1.2026e+006f, 3.26902e+006f },
 { 1.0f, 8.88611e+006f, 7.8963e+013f, 7.01674e+020f, 6.23515e+027f, 5.54062e+034f, 5.54062e+034f, 5.54062e+034f, 5.54062e+034f, 5.54062e+034f, 5.54062e+034f, 5.54062e+034f, 5.54062e+034f, 5.54062e+034f, 5.54062e+034f, 5.54062e+034f },
 { 1.0f, 0.999756f, 0.999512f, 0.999268f, 0.999024f, 0.99878f, 0.998536f, 0.998292f, 0.998049f, 0.997805f, 0.997562f, 0.997318f, 0.997075f, 0.996831f, 0.996588f, 0.996345f },
 { 1.0f, 0.996101f, 0.992218f, 0.98835f, 0.984496f, 0.980658f, 0.976835f, 0.973027f, 0.969233f, 0.965455f, 0.961691f, 0.957941f, 0.954207f, 0.950487f, 0.946781f, 0.94309f },
 { 1.0f, 0.939413f, 0.882497f, 0.829029f, 0.778801f, 0.731616f, 0.687289f, 0.645649f, 0.606531f, 0.569783f, 0.535261f, 0.502832f, 0.472367f, 0.443747f, 0.416862f, 0.391606f },
 { 1.0f, 0.367879f, 0.135335f, 0.0497871f, 0.0183156f, 0.00673795f, 0.00247875f, 0.000911882f, 0.000335463f, 0.00012341f, 4.53999e-005f, 1.67017e-005f, 6.14421e-006f, 2.26033e-006f, 8.31529e-007f, 3.05902e-007f },
 { 1.0f, 1.12535e-007f, 1.26642e-014f, 1.42516e-021f, 1.60381e-028f, 1.80485e-035f, 2.03048e-042f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f }
};

float exp_int(int value)
{
	value = value << 12;
	if (value & 0x80000000)
	{
		value = ~value + 0x00000001;
		return exp_coef[5][value & 0x0000000F] * exp_coef[6][(value >> 4) & 0x0000000F] * exp_coef[7][(value >> 8) & 0x0000000F] * exp_coef[8][(value >> 12) & 0x0000000F] * exp_coef[9][(value >> 16) & 0x0000000F];
	}
	else
	{
		return exp_coef[0][value & 0x0000000F] * exp_coef[1][(value >> 4) & 0x0000000F] * exp_coef[2][(value >> 8) & 0x0000000F] * exp_coef[3][(value >> 12) & 0x0000000F] * exp_coef[4][(value >> 16) & 0x0000000F];
	}
}


int main()
{
	std::cout << exp_double(1.2) << std::endl;
	std::cout << exp(1.2) << std::endl;

	std::cout << exp_int(2) << std::endl;
	std::cout << exp(2) << std::endl;

	return 0;
}