61 lines
1.8 KiB
C
61 lines
1.8 KiB
C
/*
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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 provided
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* that: (1) source distributions retain this entire copyright notice and
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* comment, and (2) distributions including binaries display the following
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* acknowledgement: ``This product includes software developed by the
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* University of California, Berkeley and its contributors'' in the
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* documentation or other materials provided with the distribution and in
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* all advertising materials mentioning features or use of this software.
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* Neither the name of the University nor the names of its contributors may
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* be used to endorse or promote products derived from this software without
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* specific prior written permission.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
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* WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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*/
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#ifndef lint
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static char sccsid[] = "@(#)tan.c 5.5 (Berkeley) 10/9/90";
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#endif /* not lint */
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#include "trig.h"
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double
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tan(x)
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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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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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