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#include <stdio.h>
#include <math.h>
 
float cbrt_(float x) {
	static const float T[7] = { 0.545253866f, 0.594603558f, 0.648419777f, 0.707106781f, 0.771105413f, 0.840896415f, 0.917004043f };
	static const float C0[3][8] = {
		{1.655867887f, 1.608728542f, 1.562931164f, 1.518437547f, 1.475210578f, 1.433214196f, 1.392413370f, 1.352774064f },
		{1.314263213f, 1.276848690f, 1.240499287f, 1.205184680f, 1.170875412f, 1.137542861f, 1.105159224f, 1.073697486f },
		{1.043131403f, 1.013435477f, 0.984584936f, 0.956555714f, 0.929324430f, 0.902868367f, 0.877165458f, 0.852194260f },
	};
	static const float C1[3][8] = {
		{-0.792419094f, -0.705965155f, -0.628943451f, -0.560324915f, -0.499192748f, -0.444730180f, -0.396209547f, -0.352982577f },
		{-0.628943451f, -0.560324915f, -0.499192748f, -0.444730180f, -0.396209547f, -0.352982577f, -0.314471726f, -0.280162457f },
		{-0.499192748f, -0.444730180f, -0.396209547f, -0.352982577f, -0.314471726f, -0.280162457f, -0.249596374f, -0.222365090f },
	};
 
	if (x < 0.f) {
		return -cbrt_(-x);
	}
 
	int e;
	float f = frexpf(x, &e);
	int e_div_3 = (e + 150) / 3 - 50;
	int e_mod_3 = e - e_div_3 * 3;
	int n = 3;
	int m = 4;
	for (int i = 0; i < 3; i++) {
		if (f < T[n]) {
			m >>= 1;
			n -= m;
		}
		else {
			m = (m + 1 >> 1);
			n += m;
		}
	}
	x = C0[e_mod_3][n] + C1[e_mod_3][n] * f;
	f = ldexpf(f, e_mod_3);
	x += (1.f / 3.f) * (x - f * (x * x) * (x * x));
	return ldexpf(f * (x * x), e_div_3);
}
 
int main() {
	float TABLE1[] = { 0.958102574f, 0.99999994f, 1.f };
	float TABLE2[] = { .5f, 0.545253866f, 0.594603558f, 0.648419777f, 0.707106781f, 0.771105413f, 0.840896415f, 0.917004043f };
	float TABLE3[] = { 0.125f, 0.25f, 0.5f, 1.f, 2.f, 4.f, 8.f, 16.f, 32.f, -1.f, -2.f, -4.f };
	for (float x3 : TABLE3) {
		for (float x2 : TABLE2) {
			for (float x1 : TABLE1) {
				float x = x1 * x2 * x3;
				float y1 = cbrt_(x);
				float y0 = cbrt(x);
				printf("%e\n", (double)y1 / (double)y0 - 1.);
			}
		}
	}
	return 0;
}

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Success #stdin #stdout 0s 5448KB

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Standard input is empty

stdout

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