74 lines
2.5 KiB
C
74 lines
2.5 KiB
C
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/* $NetBSD: n_tan.c,v 1.5 2003/08/07 16:44:52 agc Exp $ */
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/*
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* Copyright (c) 1987, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#ifndef lint
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#if 0
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static char sccsid[] = "@(#)tan.c 8.1 (Berkeley) 6/4/93";
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#endif
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#endif /* not lint */
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#include "mathimpl.h"
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#include "trig.h"
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double
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tan(double x)
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{
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double a,z,ss,cc,c;
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int k;
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if(!finite(x)) /* tan(NaN) and tan(INF) must be NaN */
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return x-x;
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x = drem(x,PI); /* reduce x into [-PI/2, PI/2] */
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a = copysign(x,__one); /* ... = abs(x) */
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if (a >= PIo4) {
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k = 1;
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x = copysign(PIo2-a,x);
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}
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else {
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k = 0;
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if (a < __small) {
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z=__big+a;
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return x;
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}
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}
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z = x*x;
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cc = cos__C(z);
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ss = sin__S(z);
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z *= __half; /* Next get c = cos(x) accurately */
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c = (z >= thresh ? __half-((z-__half)-cc) : __one-(z-cc));
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if (k == 0)
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return x+(x*(z-(cc-ss)))/c; /* ... sin/cos */
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#ifdef national
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else if (x == __zero)
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return copysign(fmax,x); /* no inf on 32k */
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#endif /* national */
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else
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return c/(x+x*ss); /* ... cos/sin */
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}
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