1
2/*
3 * IBM Accurate Mathematical Library
4 * written by International Business Machines Corp.
5 * Copyright (C) 2001 Free Software Foundation
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU Lesser General Public License as published by
9 * the Free Software Foundation; either version 2.1 of the License, or
10 * (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
20 */
21/**********************************************************************/
22/* MODULE_NAME:mptan.c                                                */
23/*                                                                    */
24/* FUNCTION: mptan                                                    */
25/*                                                                    */
26/* FILES NEEDED: endian.h  mpa.h                                      */
27/*               mpa.c  sincos32.c branred.c                          */
28/*                                                                    */
29/* Multi-Precision tan() function subroutine, for p=32.  It is based  */
30/* on the routines mpranred() and c32(). mpranred() performs range    */
31/* reduction of a double number x into a multiple precision number    */
32/* y, such that y=x-n*pi/2, abs(y)<pi/4, n=0,+-1,+-2,....  c32()      */
33/* computes both sin(y), cos(y).  tan(x) is either sin(y)/cos(y)      */
34/* or -cos(y)/sin(y). The precision of the result is of about 559     */
35/* significant bits.                                                  */
36/*                                                                    */
37/**********************************************************************/
38#include "endian.h"
39#include "mpa.h"
40
41int __mpranred(double, mp_no *, int);
42void __c32(mp_no *, mp_no *, mp_no *, int);
43
44void __mptan(double x, mp_no *mpy, int p) {
45
46  static const double MONE = -1.0;
47
48  int n;
49  mp_no mpw, mpc, mps;
50
51  n = __mpranred(x, &mpw, p) & 0x00000001; /* negative or positive result */
52  __c32(&mpw, &mpc, &mps, p);              /* computing sin(x) and cos(x) */
53  if (n)                     /* second or fourth quarter of unit circle */
54  { __dvd(&mpc,&mps,mpy,p);
55    mpy->d[0] *= MONE;
56  }                          /* tan is negative in this area */
57  else  __dvd(&mps,&mpc,mpy,p);
58
59  return;
60}
61