Home | History | Annotate | Line # | Download | only in noieee_src 
      1 /*	$NetBSD: n_tan.c,v 1.5 2003/08/07 16:44:52 agc Exp $	*/
      2 /*
      3  * Copyright (c) 1987, 1993
      4  *	The Regents of the University of California.  All rights reserved.
      5  *
      6  * Redistribution and use in source and binary forms, with or without
      7  * modification, are permitted provided that the following conditions
      8  * are met:
      9  * 1. Redistributions of source code must retain the above copyright
     10  *    notice, this list of conditions and the following disclaimer.
     11  * 2. Redistributions in binary form must reproduce the above copyright
     12  *    notice, this list of conditions and the following disclaimer in the
     13  *    documentation and/or other materials provided with the distribution.
     14  * 3. Neither the name of the University nor the names of its contributors
     15  *    may be used to endorse or promote products derived from this software
     16  *    without specific prior written permission.
     17  *
     18  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     28  * SUCH DAMAGE.
     29  */
     30 
     31 #ifndef lint
     32 #if 0
     33 static char sccsid[] = "@(#)tan.c	8.1 (Berkeley) 6/4/93";
     34 #endif
     35 #endif /* not lint */
     36 
     37 #include "mathimpl.h"
     38 #include "trig.h"
     39 double
     40 tan(double x)
     41 {
     42 	double a,z,ss,cc,c;
     43 	int k;
     44 
     45 	if(!finite(x))		/* tan(NaN) and tan(INF) must be NaN */
     46 		return x-x;
     47 	x = drem(x,PI);			/* reduce x into [-PI/2, PI/2] */
     48 	a = copysign(x,__one);		/* ... = abs(x) */
     49 	if (a >= PIo4) {
     50 		k = 1;
     51 		x = copysign(PIo2-a,x);
     52 	}
     53 	else {
     54 		k = 0;
     55 		if (a < __small) {
     56 			z=__big+a;
     57 			return x;
     58 		}
     59 	}
     60 	z = x*x;
     61 	cc = cos__C(z);
     62 	ss = sin__S(z);
     63 	z *= __half;			/* Next get c = cos(x) accurately */
     64 	c = (z >= thresh ? __half-((z-__half)-cc) : __one-(z-cc));
     65 	if (k == 0)
     66 		return x+(x*(z-(cc-ss)))/c;	/* ... sin/cos */
     67 #ifdef national
     68 	else if (x == __zero)
     69 		return copysign(fmax,x);	/* no inf on 32k */
     70 #endif	/* national */
     71 	else
     72 		return c/(x+x*ss);		/* ... cos/sin */
     73 }
     74