xref: /386bsd/usr/src/lib/libm/common/tan.c (revision a2142627)
1 /*
2  * Copyright (c) 1987 Regents of the University of California.
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  * 3. All advertising materials mentioning features or use of this software
14  *    must display the following acknowledgement:
15  *	This product includes software developed by the University of
16  *	California, Berkeley and its contributors.
17  * 4. Neither the name of the University nor the names of its contributors
18  *    may be used to endorse or promote products derived from this software
19  *    without specific prior written permission.
20  *
21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  */
33 
34 #ifndef lint
35 static char sccsid[] = "@(#)tan.c	5.5 (Berkeley) 10/9/90";
36 #endif /* not lint */
37 
38 #include "trig.h"
39 double
tan(x)40 tan(x)
41 double x;
42 {
43 	double a,z,ss,cc,c;
44 	int k;
45 
46 	if(!finite(x))		/* tan(NaN) and tan(INF) must be NaN */
47 		return x-x;
48 	x = drem(x,PI);			/* reduce x into [-PI/2, PI/2] */
49 	a = copysign(x,one);		/* ... = abs(x) */
50 	if (a >= PIo4) {
51 		k = 1;
52 		x = copysign(PIo2-a,x);
53 	}
54 	else {
55 		k = 0;
56 		if (a < small) {
57 			big+a;
58 			return x;
59 		}
60 	}
61 	z = x*x;
62 	cc = cos__C(z);
63 	ss = sin__S(z);
64 	z *= half;			/* Next get c = cos(x) accurately */
65 	c = (z >= thresh ? half-((z-half)-cc) : one-(z-cc));
66 	if (k == 0)
67 		return x+(x*(z-(cc-ss)))/c;	/* ... sin/cos */
68 #ifdef national
69 	else if (x == zero)
70 		return copysign(fmax,x);	/* no inf on 32k */
71 #endif	/* national */
72 	else
73 		return c/(x+x*ss);		/* ... cos/sin */
74 }
75