Simulating an ALU in java?

Question

Hi-
I am trying to simulate an ALU in java, i have written methods to do +,-,!,&&,||,^. I have different opcodes for each of the operations, I was wondering how i could use a simulated mux to pick between the different operations. I have written an 8 to 1 mux to do it, but am not sure how i would go along picking each of the operations. Also i was wondering how to do multiplication. I have each operand represented in a boolean array.
/***  ADDITION:       000
     *  SUBTRACTION:    001
     *  MULTIPLICATION: 010
     *  DIVISION:       011
     *  NOT:            100
     *  AND:            101
     *  OR:             110
     *  XOR:            111
     OPCODES
public boolean[] calc(boolean[] opcode, boolean[] left, boolean[] right) {
          boolean[] result = new boolean[WIDTH];
          boolean[] add= eightBitAdd(left,right);
          boolean[] subtract=subtract(left,right);
          boolean[] not=not(left);
          boolean[] and=and(left,right);
          boolean[] or=or(left,right);
          boolean[] xor=xor(left,right);
          System.out.println(opcode[0]+" "+opcode[1]+" "+opcode[2]+" ");
          return result; //want to set result to the array picked by the opcode, not using if statements
//two to one mux
public static boolean  twoToOne(boolean  a, boolean b, boolean s) {
          return((a&&!s)||(b&&s));
// four to one mux     
public static boolean fourToOne(boolean a, boolean b,
                        boolean c, boolean d,
                        boolean s0, boolean s1){
          return(twoToOne(twoToOne(a,b,s0),twoToOne(c,d,s0),s1));
//eight to one mux
public static boolean eightToOne(boolean a, boolean b, boolean c, boolean d,
                         boolean e, boolean f, boolean g, boolean h, boolean s0,
                        boolean s1, boolean s2){
          return(twoToOne(fourToOne(a,b,c,d,s0,s1),fourToOne(e,f,g,h,s0,s1),s2));
}Edited by: ak47 on Oct 5, 2009 7:37 PM

Answer 1

This is just an attempt, I could be wrong
Okay, I am assuming that the opcode is actually you select line data.
An 8:1 Mux has 3 select lines S0,S1,S2.
In case of multiplexer?s, if say select line data is
S2 S1 S0
1 0 0 //4and input line data is
I7 I6 I5 I4 I3 I2 I1 I0
0 1 0 1 0 0 0 1 ,then whatever is at input line I4 will propagate to the o/p. In the above case o/p = 1.
Now, as per your requirement, you want an o/p high for select line data from 000 to 111, So you need to tie up all the input data lines to logic high or Vcc. [Refer Fig|http://i34.tinypic.com/16a5vs4.jpg]
The Truth Table is as follows,
(MSB) (LSB)
S2 S1 S0 Y
0 0 0 1
0 0 1 1
0 1 0 1
0 1 1 1
1 0 0 1
1 0 1 1
1 1 0 1
1 1 1 1
Ask the user to enter the opcode (binary) as input.
Convert the input from string to int, i.e obtain the decimal equivalent of the binary input. Use Integer.parseInt(strOpcode,2) or define your
own method.
Write a switch case ( case 0 to case 7 and a default case). In every case invoke the corresponding arithmetic operation (function call) and it
is in the function that you must ask the user to enter the operand?s.