/************************************************************************
 *                                                                      *
 *                              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
 *
 *      tan   Double precision tangent
 *
 *  KEY WORDS
 *
 *      tan
 *      machine independent routines
 *      trigonometric functions
 *      math libraries
 *
 *  DESCRIPTION
 *
 *      Returns tangent of double precision floating point number.
 *
 *  USAGE
 *
 *      double tan (x)
 *      double x;
 *
 *  INTERNALS
 *
 *      Computes the tangent from tan(x) = sin(x) / cos(x).
 *
 *      If cos(x) = 0 and sin(x) >= 0, then returns largest
 *      floating point number on host machine.
 *
 *      If cos(x) = 0 and sin(x) < 0, then returns smallest
 *      floating point number on host machine.
 *
 *  REFERENCES
 *
 *      Fortran IV plus user's guide, Digital Equipment Corp. pp. B-8
 *
 */

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

static char funcname[] = "tan";

double 
tan (x)
        double x;
{
    double sinx;
    double cosx;
    struct exception xcpt;
    extern double sin ();
    extern double cos();

    sinx = sin (x);
    cosx = cos (x);
    if (cosx == 0.0) {
                xcpt.type = OVERFLOW;
                xcpt.name = funcname;
                xcpt.arg1 = x;
                if (!matherr (&xcpt)) {
                        fprintf (stderr, "%s: OVERFLOW error\n", funcname);
                        errno = ERANGE;
                        if (sinx >= 0.0) {
                                xcpt.retval = MAXDOUBLE;
                        } 
                        else {
                                xcpt.retval = -MAXDOUBLE;
                        }
                }
    } 
        else {
                xcpt.retval = sinx / cosx;
    }
        return( xcpt.retval );
}