workbench/libs/mathieeesingbas/ieeespflt.c

   1 /*
   2     Copyright © 1995-2004, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 #include "mathieeesingbas_intern.h"
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11
  12         AROS_LH1(float, IEEESPFlt,
  13
  14 /*  SYNOPSIS */
  15         AROS_LHA(LONG, y, D0),
  16
  17 /*  LOCATION */
  18         struct LibHeader *, MathIeeeSingBasBase, 6, Mathieeesingbas)
  19
  20 /*  FUNCTION
  21
  22     INPUTS
  23
  24     RESULT
  25         Flags:
  26           zero     : result is zero
  27           negative : result is negative
  28           overflow : IEEE single precision number is not exactly the integer
  29
  30     BUGS
  31
  32     INTERNALS
  33
  34 *****************************************************************************/
  35 {
  36     AROS_LIBFUNC_INIT
  37
  38     LONG Exponent = 0;
  39     LONG TestMask = 0xFFFFFFFF;
  40     LONG Res = 0;
  41
  42     if (y == 0)
  43     {
  44         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  45         return 0;
  46     }
  47
  48     if (y < 0)
  49     {
  50         Res = IEEESPSign_Mask;
  51         y= -y;
  52     }
  53     /* find out which is the number of the highest set bit */
  54     while (TestMask & y)
  55     {
  56         Exponent ++;
  57         TestMask <<= 1;
  58     }
  59
  60     if (Exponent >= 26) y >>= (Exponent - 25) & IEEESPMantisse_Mask;
  61     else                y <<= (25 - Exponent) & IEEESPMantisse_Mask;
  62
  63     if ((char) (y & 1) != 0)
  64     {
  65         y ++;
  66         if (0x02000000 == y) Exponent++;
  67     }
  68
  69     y >>= 1;
  70     y &= IEEESPMantisse_Mask;
  71
  72     Exponent += 0x7E;
  73
  74     /* adapt Exponent to IEEESP-Format */
  75     Exponent <<= 23;
  76     Res |= y | Exponent;
  77
  78     if (Res < 0) SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  79
  80     /* The resulting IEEESP is lacking precision */
  81     if (Exponent > 0x4c800000)
  82     {
  83         SetSR(Overflow_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  84     }
  85
  86     return Res;
  87
  88     AROS_LIBFUNC_EXIT
  89 }