69 lines
1.3 KiB
C
69 lines
1.3 KiB
C
/*
|
|
* (c) copyright 1989 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 <errno.h>
|
|
|
|
extern int errno;
|
|
extern double ldexp();
|
|
|
|
double
|
|
exp(x)
|
|
double x;
|
|
{
|
|
/* Algorithm and coefficients from:
|
|
"Software manual for the elementary functions"
|
|
by W.J. Cody and W. Waite, Prentice-Hall, 1980
|
|
*/
|
|
|
|
static double p[] = {
|
|
0.25000000000000000000e+0,
|
|
0.75753180159422776666e-2,
|
|
0.31555192765684646356e-4
|
|
};
|
|
|
|
static double q[] = {
|
|
0.50000000000000000000e+0,
|
|
0.56817302698551221787e-1,
|
|
0.63121894374398503557e-3,
|
|
0.75104028399870046114e-6
|
|
};
|
|
double xn, g;
|
|
int n;
|
|
int negative = x < 0;
|
|
|
|
if (x <= M_LN_MIN_D) {
|
|
if (x < M_LN_MIN_D) errno = ERANGE;
|
|
return M_MIN_D;
|
|
}
|
|
if (x >= M_LN_MAX_D) {
|
|
if (x > M_LN_MAX_D) errno = ERANGE;
|
|
return M_MAX_D;
|
|
}
|
|
if (negative) x = -x;
|
|
|
|
/* ??? avoid underflow ??? */
|
|
|
|
n = x * M_LOG2E + 0.5; /* 1/ln(2) = log2(e), 0.5 added for rounding */
|
|
xn = n;
|
|
{
|
|
double x1 = (long) x;
|
|
double x2 = x - x1;
|
|
|
|
g = ((x1-xn*0.693359375)+x2) - xn*(-2.1219444005469058277e-4);
|
|
}
|
|
if (negative) {
|
|
g = -g;
|
|
n = -n;
|
|
}
|
|
xn = g * g;
|
|
x = g * POLYNOM2(xn, p);
|
|
n += 1;
|
|
return (ldexp(0.5 + x/(POLYNOM3(xn, q) - x), n));
|
|
}
|