27 lines
438 B
C
27 lines
438 B
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 <errno.h>
|
|
|
|
double
|
|
tanh(x)
|
|
double x;
|
|
{
|
|
extern double exp();
|
|
|
|
if (x <= 0.5*M_LN_MIN_D) {
|
|
return -1;
|
|
}
|
|
if (x >= 0.5*M_LN_MAX_D) {
|
|
return 1;
|
|
}
|
|
x = exp(x + x);
|
|
return (x - 1.0)/(x + 1.0);
|
|
}
|