17 Operators: Equality and Case Equality

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
//SystemVerilogShow.com - Show a key difference between the equality and case equality operators.
// "=="   Equality operator       - returns 0,1,x
// "==="  Case Equality operator  - returns 0,1


module top;

  logic array1[3:0] = '{'b1, 'b0, 'bx, 'bz};  
  logic array2[3:0] = '{'b1, 'b0, 'bx, 'bz};  
  logic equality_result;
  logic case_equality_result;

  function void show();
    $display("  INPUTS             RESULTS");
    foreach (array1[iii]) begin
      foreach (array2[jjj]) begin
        equality_result      = (array1[iii] ==  array2[jjj]);
        case_equality_result = (array1[iii] === array2[jjj]);
        $write("(%1b vs. %1b) return (== %1b)  (=== %1b)",
                 array1[iii], array2[jjj],equality_result, case_equality_result);

        if (equality_result !== case_equality_result) begin
          $display("   --- DIFFER");
        end else begin
          $display("");
        end 
      end   
     end
  endfunction

  initial begin
    show();
    $finish();
  end
endmodule

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
  INPUTS             RESULTS
(1 vs. 1) return (== 1)  (=== 1)
(1 vs. 0) return (== 0)  (=== 0)
(1 vs. x) return (== x)  (=== 0)   --- DIFFER
(1 vs. z) return (== x)  (=== 0)   --- DIFFER
(0 vs. 1) return (== 0)  (=== 0)
(0 vs. 0) return (== 1)  (=== 1)
(0 vs. x) return (== x)  (=== 0)   --- DIFFER
(0 vs. z) return (== x)  (=== 0)   --- DIFFER
(x vs. 1) return (== x)  (=== 0)   --- DIFFER
(x vs. 0) return (== x)  (=== 0)   --- DIFFER
(x vs. x) return (== x)  (=== 1)   --- DIFFER
(x vs. z) return (== x)  (=== 0)   --- DIFFER
(z vs. 1) return (== x)  (=== 0)   --- DIFFER
(z vs. 0) return (== x)  (=== 0)   --- DIFFER
(z vs. x) return (== x)  (=== 0)   --- DIFFER
(z vs. z) return (== x)  (=== 1)   --- DIFFER
Simulation complete via $finish(1) at time 0 FS + 0