lib/libm/noieee_src/n_tan.c

   1 /*      $NetBSD: n_tan.c,v 1.5 2003/08/07 16:44:52 agc Exp $    */
   2 /*
   3  * Copyright (c) 1987, 1993
   4  *      The Regents of the University of California.  All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 3. Neither the name of the University nor the names of its contributors
  15  *    may be used to endorse or promote products derived from this software
  16  *    without specific prior written permission.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  28  * SUCH DAMAGE.
  29  */
  30
  31 #ifndef lint
  32 #if 0
  33 static char sccsid[] = "@(#)tan.c       8.1 (Berkeley) 6/4/93";
  34 #endif
  35 #endif /* not lint */
  36
  37 #include "mathimpl.h"
  38 #include "trig.h"
  39 double
  40 tan(double x)
  41 {
  42         double a,z,ss,cc,c;
  43         int k;
  44
  45         if(!finite(x))          /* tan(NaN) and tan(INF) must be NaN */
  46                 return x-x;
  47         x = drem(x,PI);                 /* reduce x into [-PI/2, PI/2] */
  48         a = copysign(x,__one);          /* ... = abs(x) */
  49         if (a >= PIo4) {
  50                 k = 1;
  51                 x = copysign(PIo2-a,x);
  52         }
  53         else {
  54                 k = 0;
  55                 if (a < __small) {
  56                         z=__big+a;
  57                         return x;
  58                 }
  59         }
  60         z = x*x;
  61         cc = cos__C(z);
  62         ss = sin__S(z);
  63         z *= __half;                    /* Next get c = cos(x) accurately */
  64         c = (z >= thresh ? __half-((z-__half)-cc) : __one-(z-cc));
  65         if (k == 0)
  66                 return x+(x*(z-(cc-ss)))/c;     /* ... sin/cos */
  67 #ifdef national
  68         else if (x == __zero)
  69                 return copysign(fmax,x);        /* no inf on 32k */
  70 #endif  /* national */
  71         else
  72                 return c/(x+x*ss);              /* ... cos/sin */
  73 }