86 lines
2.1 KiB
C
Executable File
86 lines
2.1 KiB
C
Executable File
/* tancotf.c: Computes tan or cot of a 32-bit float as outlined in [1]
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Copyright (C) 2001, 2002 Jesus Calvino-Fraga, jesusc@ieee.org
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library 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 GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
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/* [1] William James Cody and W. M. Waite. _Software manual for the
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elementary functions_, Englewood Cliffs, N.J.:Prentice-Hall, 1980. */
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/* Version 1.0 - Initial release */
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#include "math.h"
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#include <errno.h>
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#define P0 0.100000000E+1
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#define P1 -0.958017723E-1
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#define Q0 0.100000000E+1
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#define Q1 -0.429135777E+0
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#define Q2 0.971685835E-2
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#define C1 1.5703125
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#define C2 4.83826794897E-4
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#define P(f,g) (P1*g*f+f)
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#define Q(g) ((Q2*g+Q1)*g+Q0)
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//A reasonable choice for YMAX is the integer part of B**(t/2)*PI/2:
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#define YMAX 6433.0
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float tancotf(const float x, const int iscotan)
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{
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float f, g, xn, xnum, xden;
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int n;
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if (fabsf(x) > YMAX)
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{
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errno = ERANGE;
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return 0.0;
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}
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/*Round x*2*PI to the nearest integer*/
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n=(x*TWO_O_PI+(x>0.0?0.5:-0.5)); /*works for +-x*/
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xn=n;
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xnum=(int)x;
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xden=x-xnum;
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f=((xnum-xn*C1)+xden)-xn*C2;
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if (fabsf(f) < EPS)
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{
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xnum = f;
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xden = 1.0;
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}
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else
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{
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g = f*f;
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xnum = P(f,g);
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xden = Q(g);
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}
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if(n&1)
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//xn is odd
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{
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if(iscotan) return (-xnum/xden);
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else return (-xden/xnum);
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}
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else
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{
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if(iscotan) return (xden/xnum);
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else return (xnum/xden);
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}
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}
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