jehanne/sys/src/lib/jehanne/port/tanh.c

35 lines
849 B
C

/*
* This file is part of the UCB release of Plan 9. It is subject to the license
* terms in the LICENSE file found in the top-level directory of this
* distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
* part of the UCB release of Plan 9, including this file, may be copied,
* modified, propagated, or distributed except according to the terms contained
* in the LICENSE file.
*/
#include <u.h>
#include <libc.h>
/*
jehanne_tanh(arg) computes the hyperbolic tangent of its floating
point argument.
sinh and cosh are called except for large arguments, which
would cause overflow improperly.
*/
double
jehanne_tanh(double arg)
{
if(arg < 0) {
arg = -arg;
if(arg > 21)
return -1;
return -jehanne_sinh(arg)/jehanne_cosh(arg);
}
if(arg > 21)
return 1;
return jehanne_sinh(arg)/jehanne_cosh(arg);
}