sysdeps/generic/tan.c

   1 /*
   2  * Copyright (c) 1987, 1993
   3  *      The Regents of the University of California.  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       8.1 (Berkeley) 6/4/93";
  36 #endif /* not lint */
  37
  38 #include "trig.h"
  39 double
  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 }