98 lines
2.6 KiB
C
98 lines
2.6 KiB
C
/* tan.c - math routines */
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/* Copyright 1992-1993 Wind River Systems, Inc. */
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/*
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modification history
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--------------------
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01f,05feb93,jdi doc changes based on kdl review.
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01e,02dec92,jdi doc tweaks.
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01d,28oct92,jdi documentation cleanup.
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01c,21sep92,smb changed function header for mg.
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01b,20sep92,smb documentation additions
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01a,08jul92,smb documentation.
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*/
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/*
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DESCRIPTION
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* Copyright (c) 1987 Regents of the University of California.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms are permitted
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* provided that the above copyright notice and this paragraph are
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* duplicated in all such forms and that any documentation,
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* advertising materials, and other materials related to such
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* distribution and use acknowledge that the software was developed
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* by the University of California, Berkeley. The name of the
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* University may not be used to endorse or promote products derived
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* from this software without specific prior written permission.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
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* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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*
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* All recipients should regard themselves as participants in an ongoing
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* research project and hence should feel obligated to report their
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* experiences (good or bad) with these elementary function codes, using
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* the sendbug(8) program, to the authors.
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*
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SEE ALSO: American National Standard X3.159-1989
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NOMANUAL
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*/
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#include "vxWorks.h"
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#include "math.h"
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#include "private/trigP.h"
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/*******************************************************************************
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*
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* tan - compute a tangent (ANSI)
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*
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* This routine computes the tangent of <x> in double precision.
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* The angle <x> is expressed in radians.
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*
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* INCLUDE FILES: math.h
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*
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* RETURNS: The double-precision tangent of <x>.
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*
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* SEE ALSO: mathALib
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*/
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double tan
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(
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double x /* angle in radians */
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)
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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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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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