minix/lib/math/pow.c
2009-11-09 10:26:00 +00:00

54 lines
1 KiB
C

/*
* (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;
}