在systemverilog中与“ with”运算符唯一

Question

I am a new SystemVerilog user and I have faced a strange (from my point of view) behavior of combination of unique method called for fixed array with with operator.

module test();
  int arr[12] = '{1,2,1,2,3,4,5,8,9,10,10,8};
  int q[$]
  initial begin
    q = arr.unique() with (item > 5 ? item : 0);
    $display("the result is %p",q);
  end

I've expected to get queue {8,9,10} but instead I have got {1,8,9,10}.

Why there is a one at the index 0 ?

Answer 1

You are trying to combine the operation of the find method with unique . Unfortunately, it does not work the way you expect. unique returns the element, not the expression in the with clause, which is 0 for elements 1,2,3,4 and 5. The simulator could have chosen any of those elements to represent the unique value for 0(and different simulators do pick different values)

You need to write them separately:

module test();
  int arr[$] = '{1,2,1,2,3,4,5,8,9,10,10,8};
  int q[$]
  initial begin
    arr = arr.find() with (item > 5);
    q = arr.unique();
    $display("the result is %p",q);
  end

Update explaining the original results

The with clause generates a list of values to check for uniqueness

'{0,0,0,0,0,0,0,8,9,10,10,8};
  ^.            ^ ^ ^

Assuming the simulator chooses the first occurrence of a replicated value to remain, then it returns {arr[0], arr[7], arr[8], arr[9]} from the original array, which is {1,8,9,10}