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/* @(#)w_acosh.c 5.1 93/09/24 */

/*

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

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

 *

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

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

 * software is freely granted, provided that this notice

 * is preserved.

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

 *

 */

/*

FUNCTION

<<acosh>>, <<acoshf>>---inverse hyperbolic cosine

INDEX

acosh

INDEX

acoshf

ANSI_SYNOPSIS

        #include <math.h>

        double acosh(double <[x]>);

        float acoshf(float <[x]>);

TRAD_SYNOPSIS

        #include <math.h>

        double acosh(<[x]>)

        double <[x]>;

        float acoshf(<[x]>)

        float <[x]>;

DESCRIPTION

<<acosh>> calculates the inverse hyperbolic cosine of <[x]>.

<<acosh>> is defined as

@ifinfo

. log(<[x]> + sqrt(<[x]>*<[x]>-1))

@end ifinfo

@tex

$$ln\Bigl(x + \sqrt{x^2-1}\Bigr)$$

@end tex

<[x]> must be a number greater than or equal to 1.

<<acoshf>> is identical, other than taking and returning floats.

RETURNS

<<acosh>> and <<acoshf>> return the calculated value.  If <[x]>

less than 1, the return value is NaN and <<errno>> is set to <<EDOM>>.

You can change the error-handling behavior with the non-ANSI

<<matherr>> function.

PORTABILITY

Neither <<acosh>> nor <<acoshf>> are ANSI C.  They are not recommended

for portable programs.

QUICKREF ANSI SVID POSIX RENTRANT

 acos    n,n,n,m

 acosf   n,n,n,m

MATHREF

 acosh, NAN,   arg,DOMAIN,EDOM

 acosh, < 1.0, NAN,DOMAIN,EDOM

 acosh, >=1.0, acosh(arg),,,

MATHREF

 acoshf, NAN,   arg,DOMAIN,EDOM

 acoshf, < 1.0, NAN,DOMAIN,EDOM

 acoshf, >=1.0, acosh(arg),,,

*/

/*

 * wrapper acosh(x)

 */

#include "fdlibm.h"

#include <errno.h>

#ifndef _DOUBLE_IS_32BITS

#ifdef __STDC__

        double acosh(double x)          /* wrapper acosh */

#else

        double acosh(x)                 /* wrapper acosh */

        double x;

#endif

{

#ifdef _IEEE_LIBM

        return __ieee754_acosh(x);

#else

        double z;

        struct exception exc;

        z = __ieee754_acosh(x);

        if(_LIB_VERSION == _IEEE_ || isnan(x)) return z;

        if(x<1.0) {

            /* acosh(x<1) */

            exc.type = DOMAIN;

            exc.name = "acosh";

            exc.err = 0;

            exc.arg1 = exc.arg2 = x;

            exc.retval = 0.0/0.0;

            if (_LIB_VERSION == _POSIX_)

               errno = EDOM;

            else if (!matherr(&exc)) {

               errno = EDOM;

            }

            if (exc.err != 0)

               errno = exc.err;

            return exc.retval;

        } else

            return z;

#endif

}

#endif /* defined(_DOUBLE_IS_32BITS) */