newlib/libm/mathfp/s_atan.c

   1
   2 /* @(#)z_atan.c 1.0 98/08/13 */
   3
   4 /*
   5 FUNCTION
   6         <<atan>>, <<atanf>>---arc tangent
   7
   8 INDEX
   9    atan
  10 INDEX
  11    atanf
  12
  13 SYNOPSIS
  14         #include <math.h>
  15         double atan(double <[x]>);
  16         float atanf(float <[x]>);
  17
  18 DESCRIPTION
  19
  20 <<atan>> computes the inverse tangent (arc tangent) of the input value.
  21
  22 <<atanf>> is identical to <<atan>>, save that it operates on <<floats>>.
  23
  24 RETURNS
  25 @ifnottex
  26 <<atan>> returns a value in radians, in the range of -pi/2 to pi/2.
  27 @end ifnottex
  28 @tex
  29 <<atan>> returns a value in radians, in the range of $-\pi/2$ to $\pi/2$.
  30 @end tex
  31
  32 PORTABILITY
  33 <<atan>> is ANSI C.  <<atanf>> is an extension.
  34
  35 */
  36
  37 /******************************************************************
  38  * Arctangent
  39  *
  40  * Input:
  41  *   x - floating point value
  42  *
  43  * Output:
  44  *   arctan of x
  45  *
  46  * Description:
  47  *   This routine returns the arctan of x.
  48  *
  49  *****************************************************************/
  50
  51 #include "fdlibm.h"
  52 #include "zmath.h"
  53
  54 #ifndef _DOUBLE_IS_32BITS
  55
  56 double
  57 atan (double x)
  58 {
  59   switch (numtest (x))
  60     {
  61       case NAN:
  62         errno = EDOM;
  63         return (x);
  64       case INF:
  65         /* this should check to see if neg NaN or pos NaN... */
  66         return (__PI_OVER_TWO);
  67       case 0:
  68         return (0.0);
  69       default:
  70         return (atangent (x, 0, 0, 0));
  71     }
  72 }
  73
  74 #endif /* _DOUBLE_IS_32BITS */