workbench/libs/mathtrans/sptanh.c

   1 /*
   2     Copyright © 1995-2003, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 #include "mathtrans_intern.h"
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11
  12         AROS_LH1(float, SPTanh,
  13
  14 /*  SYNOPSIS */
  15         AROS_LHA(float, fnum1, D0),
  16
  17 /*  LOCATION */
  18         struct Library *, MathTransBase, 12, MathTrans)
  19
  20 /*  FUNCTION
  21         Calculate hyperbolic tangens of the ffp number
  22
  23     INPUTS
  24
  25     RESULT
  26         Motorola fast floating point number
  27
  28         flags:
  29         zero     : result is zero
  30         negative : result is negative
  31         overflow : (not possible)
  32
  33     BUGS
  34
  35     INTERNALS
  36                    ( e^x - e^(-x) )
  37         tanh(x) =  ----------------
  38                    ( e^x + e^(-x) )
  39
  40         tanh( |x| > 9 ) = 1
  41
  42 *****************************************************************************/
  43 {
  44     AROS_LIBFUNC_INIT
  45
  46     ULONG Res;
  47     LONG tmp;
  48
  49     tmp = (fnum1 & FFPExponent_Mask) - 0x41;
  50
  51     if ( tmp >= 3  &&  (fnum1 & FFPMantisse_Mask) >= 0x90000000 )
  52     {
  53         /*
  54             tanh( x > 9 ) =  1
  55             tanh( x <-9 ) = -1
  56         */
  57         return (one | ( fnum1 & FFPSign_Mask ));
  58     }
  59
  60     /* tanh(-x) = -tanh(x) */
  61     Res = SPExp(fnum1 & (FFPMantisse_Mask + FFPExponent_Mask ));
  62     Res = SPDiv
  63     (
  64         SPAdd(Res, SPDiv(Res, one)),
  65         SPAdd(Res, (ULONG)SPDiv(Res, one) | FFPSign_Mask )
  66     );
  67
  68     /* Result is zero */
  69     if (0 == Res )
  70     {
  71         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  72         return 0;
  73     }
  74
  75     /* Argument is negative -> result is negative */
  76     if ( (char) fnum1 < 0)
  77     {
  78         SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  79         return (Res | FFPSign_Mask );
  80     }
  81
  82     return Res;
  83
  84     AROS_LIBFUNC_EXIT
  85 }