/*
 * Copyright (c) 1987 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * All recipients should regard themselves as participants in an ongoing
 * research project and hence should feel obligated to report their
 * experiences (good or bad) with these elementary function codes, using
 * the sendbug(8) program, to the authors.
 */

#ifndef lint
static char sccsid[] = "@(#)tan.c	5.3 (Berkeley) 6/30/88";
#endif /* not lint */

#include "trig.h"
double
tan(x) 
double x;
{
	double a,z,ss,cc,c;
	int k;

	if(!finite(x))		/* tan(NaN) and tan(INF) must be NaN */
		return x-x;
	x = drem(x,PI);			/* reduce x into [-PI/2, PI/2] */
	a = copysign(x,one);		/* ... = abs(x) */
	if (a >= PIo4) {
		k = 1;
		x = copysign(PIo2-a,x);
	}
	else {
		k = 0;
		if (a < small) {
			big+a;
			return x;
		}
	}
	z = x*x;
	cc = cos__C(z);
	ss = sin__S(z);
	z *= half;			/* Next get c = cos(x) accurately */
	c = (z >= thresh ? half-((z-half)-cc) : one-(z-cc));
	if (k == 0)
		return x+(x*(z-(cc-ss)))/c;	/* ... sin/cos */
#ifdef national
	else if (x == zero)
		return copysign(fmax,x);	/* no inf on 32k */
#endif	/* national */
	else
		return c/(x+x*ss);		/* ... cos/sin */
}