workbench/libs/mathieeesingtrans/ieeesppow.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       Calculate y raised to the x power (y^x)
  11
  12     RESULT
  13       IEEE single precision floating point number
  14
  15
  16       flags:
  17         zero     : result is zero
  18         negative : result is negative
  19         overflow : result is too big
  20
  21     NOTES
  22
  23     EXAMPLE
  24
  25     BUGS
  26
  27     SEE ALSO
  28
  29     INTERNALS
  30
  31     HISTORY
  32 */
  33
  34 AROS_LH2(float, IEEESPPow,
  35     AROS_LHA(float, x, D1),
  36     AROS_LHA(float, y, D0),
  37     struct Library *, MathIeeeSingTransBase, 15, MathIeeeSingTrans
  38 )
  39 {
  40     AROS_LIBFUNC_INIT
  41
  42     /*
  43         a ^ b  = e^(b * ln a )
  44         y ^ x  = e^(x * ln y )
  45     */
  46     LONG Res;
  47
  48     /* y^x is illegal if y<0 and x is not an integer-value */
  49     if (y < 0 && x != IEEESPCeil(x) ) return 0;
  50
  51     Res = IEEESPLog( y & (IEEESPMantisse_Mask + IEEESPExponent_Mask) );
  52     Res = IEEESPMul(Res, x);
  53     Res = IEEESPExp(Res);
  54
  55     /*
  56         if y < 0 and x was and even integer, the result is positive, otherwise
  57         it is negative.
  58     */
  59     if (y < 0 && TRUE == intern_IEEESPisodd(x) ) Res |= IEEESPSign_Mask;
  60
  61     if (0 == Res)
  62     {
  63         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  64         return 0;
  65     }
  66
  67     SetSR(0, Zero_Bit | Negative_Bit | Overflow_Bit);
  68
  69     if ( Res < 0)
  70     {
  71         SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  72     }
  73
  74     if ( IEEESP_Pinfty == (Res & (IEEESPMantisse_Mask + IEEESPExponent_Mask)) )
  75     {
  76         /* don`t touch the Negative_Bit now!*/
  77         SetSR(Overflow_Bit, Zero_Bit | Overflow_Bit);
  78     }
  79
  80     return Res;
  81
  82     AROS_LIBFUNC_EXIT
  83 }