workbench/libs/mathieeesingbas/ieeespdiv.c

   1 /*
   2     Copyright © 1995-2014, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 #include "mathieeesingbas_intern.h"
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11
  12         AROS_LH2(float, IEEESPDiv,
  13
  14 /*  SYNOPSIS */
  15         AROS_LHA(float, y, D0),
  16         AROS_LHA(float, z, D1),
  17
  18 /*  LOCATION */
  19         struct LibHeader *, MathIeeeSingBasBase, 14, Mathieeesingbas)
  20
  21 /*  FUNCTION
  22         Divide two IEEE single precision floating point numbers
  23         x = y / z;
  24
  25     INPUTS
  26
  27     RESULT
  28         Flags:
  29           zero     : result is zero
  30           negative : result is negative
  31           overflow : result is out of range
  32
  33     BUGS
  34
  35     INTERNALS
  36         ALGORITHM:
  37         Check if fnum2 == 0: result = 0;
  38         Check if fnum1 == 0: result = overflow;
  39         The further algorithm comes down to a pen & paper division.
  40
  41 *****************************************************************************/
  42 {
  43     AROS_LIBFUNC_INIT
  44
  45     LONG Res = 0;
  46     LONG Exponent = (y & IEEESPExponent_Mask)
  47                   - (z & IEEESPExponent_Mask) + 0x3f800000;
  48
  49     LONG Mant2 = ((y & IEEESPMantisse_Mask) | 0x00800000) << 8;
  50     LONG Mant1 = ((z & IEEESPMantisse_Mask) | 0x00800000) << 8;
  51     ULONG Bit_Mask = 0x80000000;
  52
  53     if (0 == z && 0 == y) return 0x7f880000;
  54
  55     /* check if the dividend is zero */
  56     if (0 == z)
  57     {
  58         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  59         return (IEEESPExponent_Mask | ((y & IEEESPSign_Mask) ^ (z & IEEESPSign_Mask)));
  60     }
  61
  62     /* check for division by zero */
  63     if (0 == y)
  64     {
  65         SetSR(Overflow_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  66         return (y & IEEESPSign_Mask) ^ (z & IEEESPSign_Mask);
  67     }
  68
  69     while (Bit_Mask >= 0x40 && Mant2 != 0)
  70     {
  71         if (Mant2 - Mant1 >= 0)
  72         {
  73             Mant2 -= Mant1;
  74             Res |= Bit_Mask;
  75
  76             while (Mant2 > 0)
  77             {
  78                 Mant2 <<= 1;
  79                 Bit_Mask >>= 1;
  80             }
  81
  82             while (Mant1 > 0)
  83             {
  84                 Mant1 <<=1;
  85                 Bit_Mask <<=1;
  86             }
  87         } /* if */
  88         else
  89         {
  90             Mant1 = (ULONG) Mant1 >> 1;
  91             Bit_Mask >>= 1;
  92         }
  93     } /* while */
  94
  95     /* normalize the mantisse */
  96     while (Res > 0)
  97     {
  98         if (Res >= 0x40000000)
  99             Res = Res - 0x80000000;
 100         Res += Res;
 101         Exponent -=0x00800000;
 102     }
 103
 104     if ((char) Res < 0) Res += 0x00000100;
 105     Res >>= 8;
 106
 107     Res &= IEEESPMantisse_Mask;
 108     Res |= Exponent;
 109     Res |= (y & IEEESPSign_Mask) ^ (z & IEEESPSign_Mask);
 110
 111     if (Res < 0) SetSR(Negative_Bit, Zero_Bit | Overflow_Bit | Negative_Bit);
 112     if (Exponent < 0) SetSR(Overflow_Bit, Negative_Bit | Overflow_Bit);
 113
 114     return Res;
 115
 116     AROS_LIBFUNC_EXIT
 117 }