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/* @(#)z_tanf.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.
******************************************************************/
/******************************************************************
* Tangent
*
* Input:
* x - floating point value
*
* Output:
* tangent of x
*
* Description:
* This routine calculates the tangent of x.
*
*****************************************************************/
#include "fdlibm.h"
#include "zmath.h"
static const float TWO_OVER_PI = 0.6366197723;
static const float p[] = { -0.958017723e-1 };
static const float q[] = { -0.429135777,
0.971685835e-2 };
float
_DEFUN (tanf, (float),
float x)
{
float y, f, g, XN, xnum, xden, res;
int N;
/* Check for special values. */
switch (numtestf (x))
{
case NAN:
errno = EDOM;
return (x);
case INF:
errno = EDOM;
return (z_notanum_f.f);
}
y = fabsf (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 = (float) N;
f = x - N * __PI_OVER_TWO;
/* Check for values that are too small. */
if (-z_rooteps_f < f && f < z_rooteps_f)
{
xnum = f;
xden = 1.0;
}
/* Calculate the polynomial. */
else
{
g = f * f;
xnum = f * (p[0] * g) + f;
xden = (q[1] * g + q[0]) * g + 1.0;
}
/* Check for odd or even values. */
if (N & 1)
{
xnum = -xnum;
res = xden / xnum;
}
else
{
res = xnum / xden;
}
return (res);
}
#ifdef _DOUBLE_IS_32BITS
double tan (double x)
{
return (double) tanf ((float) x);
}
#endif /* _DOUBLE_IS_32BITS */
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