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