1 /*
2 * Copyright (c) 1987, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * %sccs.include.redist.c%
6 */
7
8 #ifndef lint
9 static char sccsid[] = "@(#)tan.c 8.1 (Berkeley) 06/04/93";
10 #endif /* not lint */
11
12 #include "trig.h"
13 double
tan(x)14 tan(x)
15 double x;
16 {
17 double a,z,ss,cc,c;
18 int k;
19
20 if(!finite(x)) /* tan(NaN) and tan(INF) must be NaN */
21 return x-x;
22 x = drem(x,PI); /* reduce x into [-PI/2, PI/2] */
23 a = copysign(x,one); /* ... = abs(x) */
24 if (a >= PIo4) {
25 k = 1;
26 x = copysign(PIo2-a,x);
27 }
28 else {
29 k = 0;
30 if (a < small) {
31 big+a;
32 return x;
33 }
34 }
35 z = x*x;
36 cc = cos__C(z);
37 ss = sin__S(z);
38 z *= half; /* Next get c = cos(x) accurately */
39 c = (z >= thresh ? half-((z-half)-cc) : one-(z-cc));
40 if (k == 0)
41 return x+(x*(z-(cc-ss)))/c; /* ... sin/cos */
42 #ifdef national
43 else if (x == zero)
44 return copysign(fmax,x); /* no inf on 32k */
45 #endif /* national */
46 else
47 return c/(x+x*ss); /* ... cos/sin */
48 }
49