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 41 int __mpranred(double, mp_no *, int); 42 void __c32(mp_no *, mp_no *, mp_no *, int); 43 44 void __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