134127Sbostic /*
2*61282Sbostic * Copyright (c) 1987, 1993
3*61282Sbostic * The Regents of the University of California. All rights reserved.
434127Sbostic *
542653Sbostic * %sccs.include.redist.c%
631930Szliu */
731930Szliu
831930Szliu #ifndef lint
9*61282Sbostic static char sccsid[] = "@(#)tan.c 8.1 (Berkeley) 06/04/93";
1034127Sbostic #endif /* not lint */
1131930Szliu
1231930Szliu #include "trig.h"
1331930Szliu double
tan(x)1431930Szliu tan(x)
1531930Szliu double x;
1631930Szliu {
1731930Szliu double a,z,ss,cc,c;
1831930Szliu int k;
1931930Szliu
2031930Szliu if(!finite(x)) /* tan(NaN) and tan(INF) must be NaN */
2131930Szliu return x-x;
2231930Szliu x = drem(x,PI); /* reduce x into [-PI/2, PI/2] */
2331930Szliu a = copysign(x,one); /* ... = abs(x) */
2431930Szliu if (a >= PIo4) {
2531930Szliu k = 1;
2631930Szliu x = copysign(PIo2-a,x);
2731930Szliu }
2831930Szliu else {
2931930Szliu k = 0;
3031930Szliu if (a < small) {
3131930Szliu big+a;
3231930Szliu return x;
3331930Szliu }
3431930Szliu }
3531930Szliu z = x*x;
3631930Szliu cc = cos__C(z);
3731930Szliu ss = sin__S(z);
3831930Szliu z *= half; /* Next get c = cos(x) accurately */
3931930Szliu c = (z >= thresh ? half-((z-half)-cc) : one-(z-cc));
4031930Szliu if (k == 0)
4131930Szliu return x+(x*(z-(cc-ss)))/c; /* ... sin/cos */
4231930Szliu #ifdef national
4331930Szliu else if (x == zero)
4431930Szliu return copysign(fmax,x); /* no inf on 32k */
4531930Szliu #endif /* national */
4631930Szliu else
4731930Szliu return c/(x+x*ss); /* ... cos/sin */
4831930Szliu }
49