cosh.c revision 25c28e83beb90e7c80452a7c818c5e6f73a07dc8
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright 2011 Nexenta Systems, Inc. All rights reserved.
*/
/*
* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/* INDENT OFF */
/*
* cosh(x)
* Code originated from 4.3bsd.
* Modified by K.C. Ng for SUN 4.0 libm.
* Method :
* 1. Replace x by |x| (cosh(x) = cosh(-x)).
* 2.
* [ exp(x) - 1 ]^2
* 0 <= x <= 0.3465 : cosh(x) := 1 + -------------------
* 2*exp(x)
*
* exp(x) + 1/exp(x)
* 0.3465 <= x <= 22 : cosh(x) := -------------------
* 2
* 22 <= x <= lnovft : cosh(x) := exp(x)/2
* lnovft <= x < INF : cosh(x) := scalbn(exp(x-1024*ln2),1023)
*
* Note: .3465 is a number near one half of ln2.
*
* Special cases:
* cosh(x) is |x| if x is +INF, -INF, or NaN.
* only cosh(0)=1 is exact for finite x.
*/
/* INDENT ON */
#include "libm.h"
static const double
ln2 = 6.93147180559945286227e-01,
ln2hi = 6.93147180369123816490e-01,
ln2lo = 1.90821492927058770002e-10,
lnovft = 7.09782712893383973096e+02;
double
cosh(double x) {
double t, w;
w = fabs(x);
if (!finite(w))
return (w * w);
if (w < 0.3465) {
t = expm1(w);
w = 1.0 + t;
if (w != 1.0)
w = 1.0 + (t * t) / (w + w);
return (w);
} else if (w < 22.0) {
t = exp(w);
return (0.5 * (t + 1.0 / t));
} else if (w <= lnovft) {
return (0.5 * exp(w));
} else {
if (w >= ln2)
return (_SVID_libm_err(x, x, 5));
else
}
}