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