/*

 * Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/* __ieee754_cosh(x)

 * Method :

 * mathematically cosh(x) if defined to be (exp(x)+exp(-x))/2

 *      1. Replace x by |x| (cosh(x) = cosh(-x)).

 *      2.

 *                                                      [ exp(x) - 1 ]^2

 *          0        <= x <= ln2/2  :  cosh(x) := 1 + -------------------

 *                                                         2*exp(x)

 *

 *                                                exp(x) +  1/exp(x)

 *          ln2/2    <= x <= 22     :  cosh(x) := -------------------

 *                                                        2

 *          22       <= x <= lnovft :  cosh(x) := exp(x)/2

 *          lnovft   <= x <= ln2ovft:  cosh(x) := exp(x/2)/2 * exp(x/2)

 *          ln2ovft  <  x           :  cosh(x) := huge*huge (overflow)

 *

 * Special cases:

 *      cosh(x) is |x| if x is +INF, -INF, or NaN.

 *      only cosh(0)=1 is exact for finite x.

 */

#include "fdlibm.h"

#ifdef __STDC__

static const double one = 1.0, half=0.5, huge = 1.0e300;

#else

static double one = 1.0, half=0.5, huge = 1.0e300;

#endif

#ifdef __STDC__

        double __ieee754_cosh(double x)

#else

        double __ieee754_cosh(x)

        double x;

#endif

{

        double t,w;

        int ix;

        unsigned lx;

    /* High word of |x|. */

        ix = __HI(x);

        ix &= 0x7fffffff;

    /* x is INF or NaN */

        if(ix>=0x7ff00000) return x*x;

    /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */

        if(ix<0x3fd62e43) {

            t = expm1(fabs(x));

            w = one+t;

            if (ix<0x3c800000) return w;        /* cosh(tiny) = 1 */

            return one+(t*t)/(w+w);

        }

    /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */

        if (ix < 0x40360000) {

                t = __ieee754_exp(fabs(x));

                return half*t+half/t;

        }

    /* |x| in [22, log(maxdouble)] return half*exp(|x|) */

        if (ix < 0x40862E42)  return half*__ieee754_exp(fabs(x));

    /* |x| in [log(maxdouble), overflowthresold] */

        lx = *( (((*(unsigned*)&one)>>29)) + (unsigned*)&x);

        if (ix<0x408633CE ||

              ((ix==0x408633ce)&&(lx<=(unsigned)0x8fb9f87d))) {

            w = __ieee754_exp(half*fabs(x));

            t = half*w;

            return t*w;

        }

    /* |x| > overflowthresold, cosh(x) overflow */

        return huge*huge;

}