/************************************************************************
 *                                                                      *
 *                              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
 *
 *      asin   double precision arc sine
 *
 *  KEY WORDS
 *
 *      asin
 *      machine independent routines
 *      trigonometric functions
 *      math libraries
 *
 *  DESCRIPTION
 *
 *      Returns double precision arc sine of double precision
 *      floating point argument.
 *
 *      If argument is less than -1.0 or greater than +1.0, calls
 *      matherr with a DOMAIN error.  If matherr does not handle
 *      the error then prints error message and returns 0.
 *
 *  USAGE
 *
 *      double asin (x)
 *      double x;
 *
 *  REFERENCES
 *
 *      Fortran IV-plus user's guide, Digital Equipment Corp. pp B-2.
 *
 *  RESTRICTIONS
 *
 *      For precision information refer to documentation of the floating
 *      point library primatives called.
 *      
 *  PROGRAMMER
 *
 *      Fred Fish
 *
 *  INTERNALS
 *
 *      Computes arcsine(x) from:
 *
 *              (1)     If x < -1.0 or x > +1.0 then
 *                      call matherr and return 0.0 by default.
 *
 *              (2)     If x = 0.0 then asin(x) = 0.0
 *
 *              (3)     If x = 1.0 then asin(x) = PI/2.
 *
 *              (4)     If x = -1.0 then asin(x) = -PI/2
 *
 *              (5)     If -1.0 < x < 1.0 then
 *                      asin(x) = atan(y)
 *                      y = x / sqrt[1-(x**2)]
 *
 */

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

static char funcname[] = "asin";

double asin (x)
double x;
{
    extern double atan ();
    extern double sqrt ();
    struct exception xcpt;

    DBUG_ENTER (funcname);
    DBUG_3 ("asinin", "arg %le", x);
    if ( x > 1.0 || x < -1.0) {
        xcpt.type = DOMAIN;
        xcpt.name = funcname;
        xcpt.arg1 = x;
        if (!matherr (&xcpt)) {
            fprintf (stderr, "%s: DOMAIN error\n", funcname);
            errno = EDOM;
            xcpt.retval = 0.0;
        }
    } else if (x == 0.0) {
        xcpt.retval = 0.0;
    } else if (x == 1.0) {
        xcpt.retval = HALFPI;
    } else if (x == -1.0) {
        xcpt.retval = -HALFPI;
    } else {
        xcpt.retval = atan ( x / sqrt (1.0 - (x * x)) );
    }
    DBUG_3 ("asinout", "result %le", xcpt.retval);
    DBUG_RETURN (xcpt.retval);
}