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n_tan.c revision 1.2 
      1 /*	$NetBSD: n_tan.c,v 1.2 1998/08/22 12:49:09 ragge 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. All advertising materials mentioning features or use of this software
     15  *    must display the following acknowledgement:
     16  *	This product includes software developed by the University of
     17  *	California, Berkeley and its contributors.
     18  * 4. Neither the name of the University nor the names of its contributors
     19  *    may be used to endorse or promote products derived from this software
     20  *    without specific prior written permission.
     21  *
     22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     32  * SUCH DAMAGE.
     33  */
     34 
     35 #ifndef lint
     36 #if 0
     37 static char sccsid[] = "@(#)tan.c	8.1 (Berkeley) 6/4/93";
     38 #endif
     39 #endif /* not lint */
     40 
     41 #include "mathimpl.h"
     42 #include "trig.h"
     43 double
     44 tan(x)
     45 double x;
     46 {
     47 	double a,z,ss,cc,c;
     48 	int k;
     49 
     50 	if(!finite(x))		/* tan(NaN) and tan(INF) must be NaN */
     51 		return x-x;
     52 	x = drem(x,PI);			/* reduce x into [-PI/2, PI/2] */
     53 	a = copysign(x,one);		/* ... = abs(x) */
     54 	if (a >= PIo4) {
     55 		k = 1;
     56 		x = copysign(PIo2-a,x);
     57 	}
     58 	else {
     59 		k = 0;
     60 		if (a < small) {
     61 			z=big+a;
     62 			return x;
     63 		}
     64 	}
     65 	z = x*x;
     66 	cc = cos__C(z);
     67 	ss = sin__S(z);
     68 	z *= half;			/* Next get c = cos(x) accurately */
     69 	c = (z >= thresh ? half-((z-half)-cc) : one-(z-cc));
     70 	if (k == 0)
     71 		return x+(x*(z-(cc-ss)))/c;	/* ... sin/cos */
     72 #ifdef national
     73 	else if (x == zero)
     74 		return copysign(fmax,x);	/* no inf on 32k */
     75 #endif	/* national */
     76 	else
     77 		return c/(x+x*ss);		/* ... cos/sin */
     78 }
     79