workbench/libs/mathieeesingbas/ieeespmul.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_LH2(float, IEEESPMul,
  13
  14 /*  SYNOPSIS */
  15         AROS_LHA(float, y, D0),
  16         AROS_LHA(float, z, D1),
  17
  18 /*  LOCATION */
  19         struct LibHeader *, MathIeeeSingBasBase, 13, Mathieeesingbas)
  20
  21 /*  FUNCTION
  22         Multiply two IEEE single precision numbers
  23         res = 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
  37 *****************************************************************************/
  38 {
  39     AROS_LIBFUNC_INIT
  40
  41     ULONG Mant1H = ((y & 0x00fff000) >> 12 ) | 0x00000800;
  42     ULONG Mant2H = ((z & 0x00fff000) >> 12 ) | 0x00000800;
  43     ULONG Mant1L = y & 0x00000fff;
  44     ULONG Mant2L = z & 0x00000fff;
  45     LONG Res;
  46     LONG Exponent = ((( y & IEEESPExponent_Mask))
  47                   + (( z & IEEESPExponent_Mask)) - 0x3f800000 );
  48
  49     if (0 == y || 0 == z)
  50     {
  51         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  52         return ((y & IEEESPSign_Mask) ^ (z & IEEESPSign_Mask) );
  53     }
  54
  55     Res  =  (Mant1H * Mant2H) <<  8;
  56     Res += ((Mant1H * Mant2L) >>  4);
  57     Res += ((Mant1L * Mant2H) >>  4);
  58     Res += ((Mant1L * Mant2L) >> 16);
  59
  60     /* Bit 32 is not set */
  61     if ((LONG)Res > 0) Res += Res;
  62     else               Exponent += 0x00800000;
  63
  64     /* Correction for precision */
  65     if ((char) Res < 0) Res += 0x100;
  66
  67     Res >>= 8;
  68     Res &= IEEESPMantisse_Mask;
  69
  70     Res |= ((y & IEEESPSign_Mask) ^ (z & IEEESPSign_Mask) );
  71
  72     if ( Exponent < 0)
  73     {
  74         SetSR(Overflow_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  75         return (0x7f800000 | (Res & IEEESPSign_Mask) );
  76     }
  77
  78     Res |= Exponent;
  79
  80     if ( Res < 0) SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  81
  82     return Res;
  83
  84     AROS_LIBFUNC_EXIT
  85 }