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/* @(#)z_atan.c 1.0 98/08/13 */

/*

FUNCTION

        <<atan>>, <<atanf>>---arc tangent

INDEX

   atan

INDEX

   atanf

ANSI_SYNOPSIS

        #include <math.h>

        double atan(double <[x]>);

        float atanf(float <[x]>);

TRAD_SYNOPSIS

        #include <math.h>

        double atan(<[x]>);

        double <[x]>;

        float atanf(<[x]>);

        float <[x]>;

DESCRIPTION

<<atan>> computes the inverse tangent (arc tangent) of the input value.

<<atanf>> is identical to <<atan>>, save that it operates on <<floats>>.

RETURNS

@ifnottex

<<atan>> returns a value in radians, in the range of -pi/2 to pi/2.

@end ifnottex

@tex

<<atan>> returns a value in radians, in the range of $-\pi/2$ to $\pi/2$.

@end tex

PORTABILITY

<<atan>> is ANSI C.  <<atanf>> is an extension.

*/

/******************************************************************

 * Arctangent

 *

 * Input:

 *   x - floating point value

 *

 * Output:

 *   arctan of x

 *

 * Description:

 *   This routine returns the arctan of x.

 *

 *****************************************************************/

#include "fdlibm.h"

#include "zmath.h"

#ifndef _DOUBLE_IS_32BITS

double

_DEFUN (atan, (double),

        double x)

{

  switch (numtest (x))

    {

      case NAN:

        errno = EDOM;

        return (x);

      case INF:

        /* this should check to see if neg NaN or pos NaN... */

        return (__PI_OVER_TWO);

      case 0:

        return (0.0);

      default:

        return (atangent (x, 0, 0, 0));

    }

}

#endif /* _DOUBLE_IS_32BITS */