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65 lines
2.7 KiB
C
65 lines
2.7 KiB
C
/*
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* IBM Accurate Mathematical Library
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* written by International Business Machines Corp.
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* Copyright (C) 2001, 2011 Free Software Foundation
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation; either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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/**********************************************************************/
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/* MODULE_NAME:mptan.c */
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/* */
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/* FUNCTION: mptan */
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/* */
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/* FILES NEEDED: endian.h mpa.h */
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/* mpa.c sincos32.c branred.c */
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/* */
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/* Multi-Precision tan() function subroutine, for p=32. It is based */
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/* on the routines mpranred() and c32(). mpranred() performs range */
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/* reduction of a double number x into a multiple precision number */
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/* y, such that y=x-n*pi/2, abs(y)<pi/4, n=0,+-1,+-2,.... c32() */
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/* computes both sin(y), cos(y). tan(x) is either sin(y)/cos(y) */
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/* or -cos(y)/sin(y). The precision of the result is of about 559 */
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/* significant bits. */
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/* */
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/**********************************************************************/
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#include "endian.h"
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#include "mpa.h"
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#ifndef SECTION
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# define SECTION
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#endif
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int __mpranred(double, mp_no *, int);
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void __c32(mp_no *, mp_no *, mp_no *, int);
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void
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SECTION
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__mptan(double x, mp_no *mpy, int p) {
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static const double MONE = -1.0;
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int n;
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mp_no mpw, mpc, mps;
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n = __mpranred(x, &mpw, p) & 0x00000001; /* negative or positive result */
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__c32(&mpw, &mpc, &mps, p); /* computing sin(x) and cos(x) */
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if (n) /* second or fourth quarter of unit circle */
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{ __dvd(&mpc,&mps,mpy,p);
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mpy->d[0] *= MONE;
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} /* tan is negative in this area */
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else __dvd(&mps,&mpc,mpy,p);
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return;
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}
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