rom/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     FUNCTION
  10         Calculate the sum of two IEEE single precision numbers
  11
  12     RESULT
  13         sum of y and z
  14
  15         Flags:
  16           zero     : result is zero
  17           negative : result is negative
  18           overflow : result is too large or too small for IEEESP format
  19
  20     NOTES
  21
  22     EXAMPLE
  23
  24     BUGS
  25
  26     SEE ALSO
  27
  28
  29     INTERNALS
  30
  31     HISTORY
  32 */
  33
  34 AROS_LH2(float, IEEESPAdd,
  35     AROS_LHA(float, y, D0),
  36     AROS_LHA(float, z, D1),
  37     struct LibHeader *, MathIeeeSingBasBase, 11, Mathieeesingbas
  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 }