Initial revision

lib/math/pow.c

@@ -0,0 +1,54 @@
+/*
+ * (c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
+ * See the copyright notice in the ACK home directory, in the file "Copyright".
+ *
+ * Author: Ceriel J.H. Jacobs
+ */
+/* $Header$ */
+
+#include	<math.h>
+#include	<float.h>
+#include	<errno.h>
+#include	"localmath.h"
+
+double
+pow(double x, double y)
+{
+	/*	Simple version for now. The Cody and Waite book has
+		a very complicated, much more precise version, but
+		this version has machine-dependent arrays A1 and A2,
+		and I don't know yet how to solve this ???
+	*/
+	double dummy;
+	int	result_neg = 0;
+
+	if ((x == 0 && y == 0) ||
+	    (x < 0 && modf(y, &dummy) != 0)) {
+		errno = EDOM;
+		return 0;
+	}
+
+	if (x == 0) return x;
+
+	if (x < 0) {
+		if (modf(y/2.0, &dummy) != 0) {
+			/* y was odd */
+			result_neg = 1;
+		}
+		x = -x;
+	}
+	x = log(x);
+
+	if (x < 0) {
+		x = -x;
+		y = -y;
+	}
+	/* Beware of overflow in the multiplication */
+	if (x > 1.0 && y > DBL_MAX/x) {
+		errno = ERANGE;
+		return result_neg ? -HUGE_VAL : HUGE_VAL;
+	}
+
+	x = exp(x * y);
+	return result_neg ? -x : x;
+}