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/* @(#)z_asinef.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.
******************************************************************/
/******************************************************************
* Arcsine
*
* Input:
* x - floating point value
* acosine - indicates acos calculation
*
* Output:
* Arcsine of x.
*
* Description:
* This routine calculates arcsine / arccosine.
*
*****************************************************************/
#include "fdlibm.h"
#include "zmath.h"
static const float p[] = { 0.933935835, -0.504400557 };
static const float q[] = { 0.560363004e+1, -0.554846723e+1 };
static const float a[] = { 0.0, 0.785398163 };
static const float b[] = { 1.570796326, 0.785398163 };
float
_DEFUN (asinef, (float, int),
float x _AND
int acosine)
{
int flag, i;
int branch = 0;
float g, res, R, P, Q, y;
/* Check for special values. */
i = numtestf (x);
if (i == NAN || i == INF)
{
errno = EDOM;
if (i == NAN)
return (x);
else
return (z_infinity_f.f);
}
y = fabsf (x);
flag = acosine;
if (y > 0.5)
{
i = 1 - flag;
/* Check for range error. */
if (y > 1.0)
{
errno = ERANGE;
return (z_notanum_f.f);
}
g = (1 - y) / 2.0;
y = -2 * sqrt (g);
branch = 1;
}
else
{
i = flag;
if (y < z_rooteps_f)
res = y;
else
g = y * y;
}
if (y >= z_rooteps_f || branch == 1)
{
/* Calculate the Taylor series. */
P = (p[1] * g + p[0]) * g;
Q = (g + q[1]) * g + q[0];
R = P / Q;
res = y + y * R;
}
/* Calculate asine or acose. */
if (flag == 0)
{
res = (a[i] + res) + a[i];
if (x < 0.0)
res = -res;
}
else
{
if (x < 0.0)
res = (b[i] + res) + b[i];
else
res = (a[i] - res) + a[i];
}
return (res);
}
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