workbench/libs/mathffp/spmul.c

   1 /*
   2     Copyright © 1995-2004, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 #include "mathffp_intern.h"
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11
  12         AROS_LH2(float, SPMul,
  13
  14 /*  SYNOPSIS */
  15         AROS_LHA(float, fnum1, D1),
  16         AROS_LHA(float, fnum2, D0),
  17
  18 /*  LOCATION */
  19         struct LibHeader *, MathBase, 13, Mathffp)
  20
  21 /*  FUNCTION
  22         Multiply two ffp numbers
  23         fnum = fnum1 * fnum2;
  24
  25     INPUTS
  26
  27     RESULT
  28         FFP number
  29
  30         Flags:
  31           zero     : result is zero
  32           negative : result is negative
  33           overflow : result is out of range
  34
  35     BUGS
  36
  37     INTERNALS
  38
  39 *****************************************************************************/
  40 {
  41     AROS_LIBFUNC_INIT
  42
  43     char Exponent = ((char) fnum1 & FFPExponent_Mask)
  44                   + ((char) fnum2 & FFPExponent_Mask) - 0x41;
  45     ULONG Mant1H = ( (ULONG) (fnum1 & FFPMantisse_Mask)) >> 20;
  46     ULONG Mant2H = ( (ULONG) (fnum2 & FFPMantisse_Mask)) >> 20;
  47     ULONG Mant1L = (((ULONG) (fnum1 & FFPMantisse_Mask)) >> 8) & 0x00000fff;
  48     ULONG Mant2L = (((ULONG) (fnum2 & FFPMantisse_Mask)) >> 8) & 0x00000fff;
  49     LONG Res;
  50
  51     Res  =  (Mant1H * Mant2H) <<  8;
  52     Res += ((Mant1H * Mant2L) >>  4);
  53     Res += ((Mant1L * Mant2H) >>  4);
  54     Res += ((Mant1L * Mant2L) >> 16);
  55     Res &= FFPMantisse_Mask;
  56
  57     /* Bit 32 is not set */
  58     if ((LONG)Res > 0)
  59     {
  60         Res <<= 1; /* rotate the mantisse by one bit to the left */
  61     }
  62     else
  63     {
  64         Exponent ++;
  65     }
  66
  67     if (0 == Res)
  68     {
  69         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  70         return 0;
  71     }
  72
  73     Res |= ((fnum1 & FFPSign_Mask) ^ (fnum2 & FFPSign_Mask) );
  74
  75     /* overflow? */
  76     if ((char) Exponent < 0 || (char) Exponent == 0x7f)
  77     {
  78         SetSR(Overflow_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  79         D(kprintf("SPMul(%x * %x) = %x\n",fnum1,fnum2,Res));
  80         return (Res | (FFPMantisse_Mask + FFPExponent_Mask));
  81     }
  82
  83     Res |= Exponent;
  84
  85     if ((char) Res < 0)
  86     {
  87         SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  88     }
  89
  90     D(kprintf("SPMul(%x * %x) = %x\n", fnum1, fnum2, Res));
  91
  92     return Res;
  93
  94     AROS_LIBFUNC_EXIT
  95 }