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     FUNCTION
  10       Calculate hyperbolic tangens of the ffp number
  11
  12     RESULT
  13       Motorola fast 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      <code>
  30
  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, SPTanh,
  42     AROS_LHA(float, fnum1, D0),
  43     struct Library *, MathTransBase, 12, MathTrans
  44 )
  45 {
  46     AROS_LIBFUNC_INIT
  47
  48     ULONG Res;
  49     LONG tmp;
  50
  51     tmp = (fnum1 & FFPExponent_Mask) - 0x41;
  52
  53     if ( tmp >= 3  &&  (fnum1 & FFPMantisse_Mask) >= 0x90000000 )
  54     {
  55         /*
  56             tanh( x > 9 ) =  1
  57             tanh( x <-9 ) = -1
  58         */
  59         return (one | ( fnum1 & FFPSign_Mask ));
  60     }
  61
  62     /* tanh(-x) = -tanh(x) */
  63     Res = SPExp(fnum1 & (FFPMantisse_Mask + FFPExponent_Mask ));
  64     Res = SPDiv
  65     (
  66         SPAdd(Res, SPDiv(Res, one)),
  67         SPAdd(Res, (ULONG)SPDiv(Res, one) | FFPSign_Mask )
  68     );
  69
  70     /* Result is zero */
  71     if (0 == Res )
  72     {
  73         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  74         return 0;
  75     }
  76
  77     /* Argument is negative -> result is negative */
  78     if ( (char) fnum1 < 0)
  79     {
  80         SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  81         return (Res | FFPSign_Mask );
  82     }
  83
  84     return Res;
  85
  86     AROS_LIBFUNC_EXIT
  87 }