sysdeps/ieee754/dbl-64/mptan.c

   1 /*
   2  * IBM Accurate Mathematical Library
   3  * written by International Business Machines Corp.
   4  * Copyright (C) 2001-2014 Free Software Foundation, Inc.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU Lesser General Public License as published by
   8  * the Free Software Foundation; either version 2.1 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  18  */
  19 /**********************************************************************/
  20 /* MODULE_NAME:mptan.c                                                */
  21 /*                                                                    */
  22 /* FUNCTION: mptan                                                    */
  23 /*                                                                    */
  24 /* FILES NEEDED: endian.h  mpa.h                                      */
  25 /*               mpa.c  sincos32.c branred.c                          */
  26 /*                                                                    */
  27 /* Multi-Precision tan() function subroutine, for p=32.  It is based  */
  28 /* on the routines mpranred() and c32(). mpranred() performs range    */
  29 /* reduction of a double number x into a multiple precision number    */
  30 /* y, such that y=x-n*pi/2, abs(y)<pi/4, n=0,+-1,+-2,....  c32()      */
  31 /* computes both sin(y), cos(y).  tan(x) is either sin(y)/cos(y)      */
  32 /* or -cos(y)/sin(y). The precision of the result is of about 559     */
  33 /* significant bits.                                                  */
  34 /*                                                                    */
  35 /**********************************************************************/
  36 #include "endian.h"
  37 #include "mpa.h"
  38
  39 #ifndef SECTION
  40 # define SECTION
  41 #endif
  42
  43 void
  44 SECTION
  45 __mptan (double x, mp_no *mpy, int p)
  46 {
  47   int n;
  48   mp_no mpw, mpc, mps;
  49
  50   /* Negative or positive result.  */
  51   n = __mpranred (x, &mpw, p) & 0x00000001;
  52   /* Computing sin(x) and cos(x).  */
  53   __c32 (&mpw, &mpc, &mps, p);
  54   /* Second or fourth quarter of unit circle.  */
  55   if (n)
  56     {
  57       __dvd (&mpc, &mps, mpy, p);
  58       mpy->d[0] *= -1;
  59     }
  60   /* tan is negative in this area.  */
  61   else
  62     __dvd (&mps, &mpc, mpy, p);
  63 }