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     FUNCTION
  10       Calculates the angle of a given number representing the tangent
  11       of that angle. The angle will be in radians.
  12
  13
  14     RESULT
  15       IEEE single precision floating point number
  16
  17     NOTES
  18
  19     EXAMPLE
  20
  21     BUGS
  22
  23     SEE ALSO
  24
  25     INTERNALS
  26
  27     HISTORY
  28 */
  29
  30 AROS_LH1(float, IEEESPAtan,
  31     AROS_LHA(float, y, D0),
  32     struct Library *, MathIeeeSingTransBase, 5, MathIeeeSingTrans
  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 */