era.mi/src/era/mi/logic/Bit.java

   1 package era.mi.logic;
   2
   3 public enum Bit
   4 {
   5         ONE, ZERO, Z, X;
   6
   7         public static Bit and(Bit a, Bit b)
   8         {
   9                 return a.and(b);
  10         }
  11
  12         public Bit and(Bit other)
  13         {
  14                 if (equals(Bit.ZERO) || other.equals(Bit.ZERO))
  15                         return Bit.ZERO;
  16                 else if (equals(other) && equals(Bit.ONE))
  17                         return Bit.ONE;
  18                 else
  19                         return Bit.X;
  20         }
  21
  22         public static Bit or(Bit a, Bit b)
  23         {
  24                 return a.or(b);
  25         }
  26
  27         public Bit or(Bit other)
  28         {
  29                 if (equals(Bit.ONE) || other.equals(Bit.ONE))
  30                         return Bit.ONE;
  31                 else if (equals(other) && equals(Bit.ZERO))
  32                         return Bit.ZERO;
  33                 else
  34                         return Bit.X;
  35         }
  36
  37         public static Bit xor(Bit a, Bit b)
  38         {
  39                 return a.xor(b);
  40         }
  41
  42         public Bit xor(Bit other)
  43         {
  44                 // I'm uncertain how this should behave for cases where one value is neither 1 nor 0.
  45                 // TODO: Implement xor
  46                 return Bit.X;
  47         }
  48
  49         public Bit not()
  50         {
  51                 switch (this)
  52                         {
  53                         case ONE:
  54                                 return Bit.ZERO;
  55                         case ZERO:
  56                                 return Bit.ONE;
  57                         default:
  58                                 return Bit.X;
  59                         }
  60         }
  61
  62         /**
  63          * Rules for two bits that get directly connected<br>
  64          * <code><table>
  65          * <tbody>
  66          * <tr><td><td>X<td>0<td>1<td>Z</tr>
  67          * <tr><td>X<td>X<td>X<td>X<td>X</tr>
  68          * <tr><td>0<td>X<td>0<td>X<td>0</tr>
  69          * <tr><td>1<td>X<td>X<td>1<td>1</tr>
  70          * <tr><td>Z<td>X<td>0<td>1<td>Z</tr>
  71          * </tbody>
  72          * </table><code>
  73          *
  74          * @return the result according to the table
  75          *
  76          * @author Christian Femers
  77          */
  78         public Bit combineWith(Bit other)
  79         {
  80                 if (this == other)
  81                         return this;
  82                 if (this == X || other == X)
  83                         return X;
  84                 if (other == Z)
  85                         return this;
  86                 if (this == Z)
  87                         return other;
  88                 return X;
  89         }
  90
  91         public static Bit combine(Bit a, Bit b)
  92         {
  93                 return a.combineWith(b);
  94         }
  95 }