BSD 4_3_Reno release

[unix-history] / usr / src / lib / libm / common / tan.c

/*
* Copyright (c) 1987 Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms are permitted
* provided that: (1) source distributions retain this entire copyright
* notice and comment, and (2) distributions including binaries display
* the following acknowledgement:  ``This product includes software
* developed by the University of California, Berkeley and its contributors''
* in the documentation or other materials provided with the distribution
* and in all advertising materials mentioning features or use of this
* software. Neither the name of the University nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
* All recipients should regard themselves as participants in an ongoing
* research project and hence should feel obligated to report their
* experiences (good or bad) with these elementary function codes, using
* the sendbug(8) program, to the authors.
*/

#ifndef lint
static char sccsid[] = "@(#)tan.c       5.4 (Berkeley) 6/1/90";
#endif /* not lint */

#include "trig.h"
double
tan(x) 
double x;
{
       double a,z,ss,cc,c;
       int k;

       if(!finite(x))          /* tan(NaN) and tan(INF) must be NaN */
               return x-x;
       x = drem(x,PI);                 /* reduce x into [-PI/2, PI/2] */
       a = copysign(x,one);            /* ... = abs(x) */
       if (a >= PIo4) {
               k = 1;
               x = copysign(PIo2-a,x);
       }
       else {
               k = 0;
               if (a < small) {
                       big+a;
                       return x;
               }
       }
       z = x*x;
       cc = cos__C(z);
       ss = sin__S(z);
       z *= half;                      /* Next get c = cos(x) accurately */
       c = (z >= thresh ? half-((z-half)-cc) : one-(z-cc));
       if (k == 0)
               return x+(x*(z-(cc-ss)))/c;     /* ... sin/cos */
#ifdef national
       else if (x == zero)
               return copysign(fmax,x);        /* no inf on 32k */
#endif  /* national */
       else
               return c/(x+x*ss);              /* ... cos/sin */
}