55 lines
1.1 KiB
C
55 lines
1.1 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
|
|
*/
|
|
/* $Id$ */
|
|
|
|
#include <float.h>
|
|
#include <math.h>
|
|
#include <errno.h>
|
|
#include "localmath.h"
|
|
|
|
double
|
|
tanh(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[] = {
|
|
-0.16134119023996228053e+4,
|
|
-0.99225929672236083313e+2,
|
|
-0.96437492777225469787e+0
|
|
};
|
|
static double q[] = {
|
|
0.48402357071988688686e+4,
|
|
0.22337720718962312926e+4,
|
|
0.11274474380534949335e+3,
|
|
1.0
|
|
};
|
|
int negative = x < 0;
|
|
|
|
if (__IsNan(x)) {
|
|
errno = EDOM;
|
|
return x;
|
|
}
|
|
if (negative) x = -x;
|
|
|
|
if (x >= 0.5*M_LN_MAX_D) {
|
|
x = 1.0;
|
|
}
|
|
#define LN3D2 0.54930614433405484570e+0 /* ln(3)/2 */
|
|
else if (x > LN3D2) {
|
|
x = 0.5 - 1.0/(exp(x+x)+1.0);
|
|
x += x;
|
|
}
|
|
else {
|
|
/* ??? avoid underflow ??? */
|
|
double g = x*x;
|
|
x += x * g * POLYNOM2(g, p)/POLYNOM3(g, q);
|
|
}
|
|
return negative ? -x : x;
|
|
}
|