/************************************************************************
 *                                                                      *
 *                              N O T I C E                             *
 *                                                                      *
 *                      Copyright Abandoned, 1987, Fred Fish            *
 *                                                                      *
 *      This previously copyrighted work has been placed into the       *
 *      public domain by the author (Fred Fish) and may be freely used  *
 *      for any purpose, private or commercial.  I would appreciate     *
 *      it, as a courtesy, if this notice is left in all copies and     *
 *      derivative works.  Thank you, and enjoy...                      *
 *                                                                      *
 *      The author makes no warranty of any kind with respect to this   *
 *      product and explicitly disclaims any implied warranties of      *
 *      merchantability or fitness for any particular purpose.          *
 *                                                                      *
 ************************************************************************
 */

/*
 *  FUNCTION
 *
 *      acosh   double precision hyperbolic arc cosine
 *
 *  KEY WORDS
 *
 *      acosh
 *      machine independent routines
 *      math libraries
 *
 *  DESCRIPTION
 *
 *      Returns double precision hyperbolic arc cosine of double precision
 *      floating point number.
 *
 *  USAGE
 *
 *      double acosh (x)
 *      double x;
 *
 *  RESTRICTIONS
 *
 *      The range of the ACOSH function is all real numbers greater
 *      than or equal to 1.0 however large arguments may cause
 *      overflow in the x squared portion of the function evaluation.
 *
 *      For precision information refer to documentation of the
 *      floating point library primatives called.
 *      
 *  PROGRAMMER
 *
 *      Fred Fish
 *
 *  INTERNALS
 *
 *      Computes acosh(x) from:
 *
 *              1.      If x < 1.0 then report illegal
 *                      argument and return zero.
 *
 *              2.      If x > sqrt(MAXDOUBLE) then
 *                      set x = sqrt(MAXDOUBLE and
 *                      continue after reporting overflow.
 *
 *              3.      acosh(x) = log [x+sqrt(x**2 - 1)]
 *
 */

#include <stdio.h>
#include "pml.h"

static char funcname[] = "acosh";

double acosh (x)
double x;
{
    struct exception xcpt;
    extern double log ();
    extern double sqrt ();

    DBUG_ENTER (funcname);
    DBUG_3 ("acoshin", "arg %le", x);
    if (x < 1.0) {
        xcpt.type = DOMAIN;
        xcpt.name = funcname;
        xcpt.arg1 = x;
        if (!matherr (&xcpt)) {
            fprintf (stderr, "%s: DOMAIN error\n", funcname);
            errno = ERANGE;
            xcpt.retval = 0.0;
        }
    } else if (x > SQRT_MAXDOUBLE) {
        xcpt.type = OVERFLOW;
        xcpt.name = funcname;
        xcpt.arg1 = x;
        if (!matherr (&xcpt)) {
            fprintf (stderr, "%s: OVERFLOW error\n", funcname);
            errno = ERANGE;
            x = SQRT_MAXDOUBLE;
            xcpt.retval = log (2* SQRT_MAXDOUBLE);
        }
    } else {
        xcpt.retval = log (x + sqrt (x*x - 1.0));
    }
    DBUG_3 ("acoshout", "result %le", xcpt.retval);
    DBUG_RETURN (xcpt.retval);
}