workbench/libs/mathieeesingtrans/ieeespatan.c

   1 /*
   2     Copyright © 1995-2003, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 #include "mathieeesingtrans_intern.h"
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11
  12         AROS_LH1(float, IEEESPAtan,
  13
  14 /*  SYNOPSIS */
  15         AROS_LHA(float, y, D0),
  16
  17 /*  LOCATION */
  18         struct Library *, MathIeeeSingTransBase, 5, MathIeeeSingTrans)
  19
  20 /*  FUNCTION
  21         Calculates the angle of a given number representing the tangent
  22         of that angle. The angle will be in radians.
  23
  24     INPUTS
  25
  26     RESULT
  27         IEEE single precision floating point number
  28
  29     BUGS
  30
  31     INTERNALS
  32
  33 *****************************************************************************/
  34 {
  35     AROS_LIBFUNC_INIT
  36
  37     LONG yabs = y & (IEEESPMantisse_Mask | IEEESPExponent_Mask);
  38     LONG ysquared, ycubed;
  39
  40     /* check for +- infinity -> output: +-pi/2 */
  41     if (IEEESP_Pinfty == yabs) return (pio2 | (y & IEEESPSign_Mask));
  42
  43     /* atan(0) = 0 */
  44     if (0 == yabs)
  45     {
  46         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  47         return 0;
  48     }
  49
  50     /* atan(x >= 128) = pi/2 - 1/x */
  51     if ( (yabs & IEEESPExponent_Mask) >= 0x43000000)
  52     {
  53         if (yabs == y) /* arg has ppositive sign */
  54         {
  55             SetSR(0, Zero_Bit | Negative_Bit | Overflow_Bit);
  56             return IEEESPSub(pio2,IEEESPDiv(one,yabs));
  57         }
  58         else
  59         {
  60             SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  61             return (IEEESPSub(pio2,IEEESPDiv(one,yabs))) | IEEESPSign_Mask;
  62         }
  63     }
  64
  65     /* atan(x >= 64) = pi/2 - 1/x +1/(3*x^3) */
  66
  67     ysquared = IEEESPMul(yabs, yabs);
  68
  69     if( (yabs & IEEESPExponent_Mask) >= 0x42000000)
  70     {
  71         ycubed   = IEEESPMul(yabs, ysquared);
  72
  73         /* pi/2 - 1/x + 1/(3*x^3) = pi/2 + (1-3*x^2)/(3*x^3)*/
  74         if (yabs == y) /* arg has positive sign */
  75         {
  76             SetSR(0, Zero_Bit | Negative_Bit | Overflow_Bit);
  77             return IEEESPAdd
  78             (
  79                 pio2, IEEESPDiv
  80                 (
  81                     IEEESPAdd
  82                     (
  83                         IEEESPMul(three, ysquared) | IEEESPSign_Mask, one
  84                     ),
  85                     IEEESPMul(three, ycubed)
  86                 )
  87             );
  88         }
  89         else
  90         {
  91             SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  92             return IEEESPAdd
  93             (
  94                 pio2, IEEESPDiv
  95                 (
  96                     IEEESPAdd
  97                     (
  98                         IEEESPMul(three, ysquared) | IEEESPSign_Mask, one
  99                     ),
 100                     IEEESPMul(three, ycubed)
 101                 )
 102             ) | IEEESPSign_Mask;
 103         }
 104     }
 105
 106     /* atan(x <= 64) */
 107     return IEEESPAsin(IEEESPDiv(y,IEEESPSqrt(IEEESPAdd(one,ysquared))));
 108
 109     AROS_LIBFUNC_EXIT
 110 } /* IEEESPAtan */