tasks a-s

Task/Nth-root/C/nth-root.c

@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <float.h>
+
+inline double abs_(double x) { return x >= 0 ? x : -x; }
+double pow_(double x, int e)
+{
+	double ret = 1;
+	for (ret = 1; e; x *= x, e >>= 1)
+		if ((e & 1)) ret *= x;
+	return ret;
+}
+
+double root(double a, int n)
+{
+	double d, x = 1;
+	if (!a) return 0;
+	if (n < 1 || (a < 0 && !(n&1))) return 0./0.; /* NaN */
+
+	do {	d = (a / pow_(x, n - 1) - x) / n;
+		x+= d;
+	} while (abs_(d) >= abs_(x) * (DBL_EPSILON * 10));
+
+	return x;
+}
+
+int main()
+{
+	double x = pow_(-3.14159, 15);
+	printf("root(%g, 15) = %g\n", x, root(x, 15));
+	return 0;
+}