workbench/libs/mathieeesingbas/ieeespadd.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, IEEESPAdd,
  13
  14 /*  SYNOPSIS */
  15         AROS_LHA(float, y, D0),
  16         AROS_LHA(float, z, D1),
  17
  18 /*  LOCATION */
  19         struct LibHeader *, MathIeeeSingBasBase, 11, Mathieeesingbas)
  20
  21 /*  FUNCTION
  22         Calculate the sum of two IEEE single precision numbers
  23
  24     INPUTS
  25
  26     RESULT
  27         sum of y and z
  28
  29         Flags:
  30           zero     : result is zero
  31           negative : result is negative
  32           overflow : result is too large or too small for IEEESP format
  33
  34     BUGS
  35
  36     INTERNALS
  37
  38 *****************************************************************************/
  39 {
  40     AROS_LIBFUNC_INIT
  41
  42     LONG Res;
  43     LONG Mant1, Mant2;
  44     LONG Shift;
  45     LONG Exponent;
  46
  47     SetSR(0, Zero_Bit | Overflow_Bit | Negative_Bit );
  48
  49     Shift = ((y & IEEESPExponent_Mask) -
  50            (z & IEEESPExponent_Mask)) >> 23;
  51
  52     if (y != 0 && y != IEEESPSign_Mask )
  53     {
  54         Mant1 = (y & IEEESPMantisse_Mask) | 0x00800000;
  55     }
  56     else
  57     {
  58         Mant1 = 0;
  59     }
  60
  61     if (z != 0 && z != IEEESPSign_Mask )
  62     {
  63         Mant2 = (z & IEEESPMantisse_Mask) | 0x00800000;
  64     }
  65     else
  66     {
  67         Mant2 = 0;
  68     }
  69
  70     if (Shift > 0)
  71     {
  72         Mant2 >>= Shift;
  73         Exponent = (y & IEEESPExponent_Mask);
  74     }
  75     else
  76     {
  77         Mant1 >>= (-Shift);
  78         Exponent = (z & IEEESPExponent_Mask);
  79     }
  80
  81     /* sign(fnum1) == sign(fnum2)
  82     ** simple addition
  83     ** 0.25 <= res < 1
  84     */
  85     if ( (z & IEEESPSign_Mask) - ( y & IEEESPSign_Mask) == 0)
  86     {
  87         Res = y & IEEESPSign_Mask;
  88         Mant1 += Mant2;
  89         if ( (Mant1 & 0x01000000) != 0)
  90         {
  91             Exponent += 0x00800000;
  92             Mant1 >>= 1;
  93         }
  94         Mant1 &= IEEESPMantisse_Mask;
  95     }
  96     /* second case: sign(fnum1) != sign(fnum2)
  97     **   -1 <= res < 1
  98     */
  99     else
 100     {
 101         if ( y < 0)
 102         {
 103             Mant1 = Mant2 - Mant1;
 104         }
 105         else /* fnum2 < 0 */
 106         {
 107             Mant1 = Mant1 - Mant2;
 108         }
 109         /*if the result is below zero */
 110         if (  Mant1 < 0)
 111         {
 112             Res = IEEESPSign_Mask;
 113             Mant1 =-Mant1;
 114             SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
 115         }
 116         else
 117         {
 118             Res = 0;
 119         }
 120
 121         if (0 == Mant1)
 122         {
 123             SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
 124             return 0;
 125         }
 126         else
 127         {
 128             /* normalize the mantisse */
 129             while ( (Mant1 & 0x00800000) == 0)
 130             {
 131                 Mant1 += Mant1;  /*one bit to the left. */
 132                 Exponent -= 0x00800000;
 133             }
 134             Mant1 &= IEEESPMantisse_Mask;
 135         } /* else */
 136
 137     } /* else */
 138
 139     if ( Exponent < 0)
 140     {
 141         SetSR(Overflow_Bit, Zero_Bit | Overflow_Bit);
 142         /* do NOT change Negative_Bit! */
 143         return (Res | (IEEESPMantisse_Mask | IEEESPExponent_Mask));
 144     }
 145
 146     Res |= Mant1 | Exponent;
 147     return Res;
 148
 149     AROS_LIBFUNC_EXIT
 150 }