131 lines
2.7 KiB
C
131 lines
2.7 KiB
C
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/* @(#)z_tan.c 1.0 98/08/13 */
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/******************************************************************
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* The following routines are coded directly from the algorithms
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* and coefficients given in "Software Manual for the Elementary
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* Functions" by William J. Cody, Jr. and William Waite, Prentice
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* Hall, 1980.
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******************************************************************/
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/*
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FUNCTION
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<<tan>>, <<tanf>>---tangent
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INDEX
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tan
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INDEX
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tanf
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SYNOPSIS
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#include <math.h>
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double tan(double <[x]>);
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float tanf(float <[x]>);
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DESCRIPTION
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<<tan>> computes the tangent of the argument <[x]>.
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Angles are specified in radians.
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<<tanf>> is identical, save that it takes and returns <<float>> values.
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RETURNS
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The tangent of <[x]> is returned.
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PORTABILITY
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<<tan>> is ANSI. <<tanf>> is an extension.
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*/
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/******************************************************************
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* Tangent
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*
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* Input:
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* x - floating point value
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*
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* Output:
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* tangent of x
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*
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* Description:
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* This routine calculates the tangent of x.
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*
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*****************************************************************/
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#include "fdlibm.h"
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#include "zmath.h"
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#ifndef _DOUBLE_IS_32BITS
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static const double TWO_OVER_PI = 0.63661977236758134308;
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static const double p[] = { -0.13338350006421960681,
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0.34248878235890589960e-2,
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-0.17861707342254426711e-4 };
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static const double q[] = { -0.46671683339755294240,
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0.25663832289440112864e-1,
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-0.31181531907010027307e-3,
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0.49819433993786512270e-6 };
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double
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_DEFUN (tan, (double),
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double x)
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{
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double y, f, g, XN, xnum, xden, res;
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int N;
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/* Check for special values. */
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switch (numtest (x))
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{
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case NAN:
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errno = EDOM;
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return (x);
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case INF:
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errno = EDOM;
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return (z_notanum.d);
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}
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y = fabs (x);
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/* Check for values that are out of our range. */
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if (y > 105414357.0)
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{
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errno = ERANGE;
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return (y);
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}
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if (x < 0.0)
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N = (int) (x * TWO_OVER_PI - 0.5);
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else
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N = (int) (x * TWO_OVER_PI + 0.5);
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XN = (double) N;
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f = x - N * __PI_OVER_TWO;
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/* Check for values that are too small. */
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if (-z_rooteps < f && f < z_rooteps)
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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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/* Calculate the polynomial. */
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else
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{
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g = f * f;
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xnum = f * ((p[2] * g + p[1]) * g + p[0]) * g + f;
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xden = (((q[3] * g + q[2]) * g + q[1]) * g + q[0]) * g + 1.0;
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}
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if (N & 1)
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{
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xnum = -xnum;
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res = xden / xnum;
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}
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else
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{
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res = xnum / xden;
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}
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return (res);
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}
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#endif /* _DOUBLE_IS_32BITS */
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