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//===========================================================================

//

//      e_cosh.c

//

//      Part of the standard mathematical function library

//

//===========================================================================

//####ECOSGPLCOPYRIGHTBEGIN####

// -------------------------------------------

// This file is part of eCos, the Embedded Configurable Operating System.

// Copyright (C) 1998, 1999, 2000, 2001, 2002 Red Hat, Inc.

//

// eCos is free software; you can redistribute it and/or modify it under

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// or inline functions from this file, or you compile this file and link it

// with other works to produce a work based on this file, this file does not

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//####ECOSGPLCOPYRIGHTEND####

//===========================================================================

//#####DESCRIPTIONBEGIN####

//

// Author(s):   jlarmour

// Contributors:  jlarmour

// Date:        1998-02-13

// Purpose:     

// Description: 

// Usage:       

//

//####DESCRIPTIONEND####

//

//===========================================================================

// CONFIGURATION

#include <pkgconf/libm.h>   // Configuration header

// Include the Math library?

#ifdef CYGPKG_LIBM     

// Derived from code with the following copyright

/* @(#)e_cosh.c 1.3 95/01/18 */

/*

 * ====================================================

 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.

 *

 * Developed at SunSoft, a Sun Microsystems, Inc. business.

 * Permission to use, copy, modify, and distribute this

 * software is freely granted, provided that this notice

 * is preserved.

 * ====================================================

 */

/* __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 "mathincl/fdlibm.h"

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

        double __ieee754_cosh(double x)

{

        double t,w;

        int ix;

        unsigned lx;

    /* High word of |x|. */

        ix = CYG_LIBM_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;

}

#endif // ifdef CYGPKG_LIBM     

// EOF e_cosh.c