workbench/libs/mathieeesingtrans/ieeesptanh.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 hyperbolic tangens of the IEEE single precision number
  11
  12     RESULT
  13       IEEE single precision floating point number
  14
  15       flags:
  16         zero     : result is zero
  17         negative : result is negative
  18         overflow : (not possible)
  19
  20     NOTES
  21
  22     EXAMPLE
  23
  24     BUGS
  25
  26     SEE ALSO
  27
  28     INTERNALS
  29
  30       <code>
  31                 ( e^x - e^(-x) )
  32      tanh(x) =  ----------------
  33                 ( e^x + e^(-x) )
  34
  35      tanh( |x| >= 9 ) = 1
  36       </code>
  37
  38     HISTORY
  39 */
  40
  41 AROS_LH1(float, IEEESPTanh,
  42     AROS_LHA(float, y, D0),
  43     struct Library *, MathIeeeSingTransBase, 12, MathIeeeSingTrans
  44 )
  45 {
  46     AROS_LIBFUNC_INIT
  47
  48     LONG Res;
  49     LONG y2 = y & (IEEESPMantisse_Mask + IEEESPExponent_Mask );
  50     LONG tmp;
  51
  52     if ( y2 >= 0x41100000 )
  53     /*
  54         tanh( x > 9 ) =  1
  55         tanh( x <-9 ) = -1
  56     */
  57     return (one | ( y & IEEESPSign_Mask ));
  58
  59     /* tanh(-x) = -tanh(x) */
  60     Res = IEEESPExp(y2);
  61     tmp = IEEESPDiv(one, Res);
  62     Res = IEEESPDiv
  63     (
  64         IEEESPAdd(Res, (tmp | IEEESPSign_Mask) ),
  65         IEEESPAdd(Res, tmp)
  66     );
  67
  68     /* Result is zero */
  69     if (0 == Res )
  70     {
  71         if (y < 0)
  72         {
  73             SetSR(Zero_Bit | Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  74         }
  75         else
  76         {
  77             SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  78         }
  79
  80         return (y & IEEESPSign_Mask);
  81     }
  82
  83     /* Argument is negative -> result is negative */
  84     if ( y < 0)
  85     {
  86         SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  87         return (Res | IEEESPSign_Mask );
  88     }
  89
  90     return Res;
  91
  92     AROS_LIBFUNC_EXIT
  93 }