How to constrain SystemVerilog queue to values in another queue?

Question

Is there a way to populate a queue using elements from another random queue in a constraint-based way? For example,

class some_class;
  
  rand bit [7:0] choices [$];
  rand bit [7:0] chosen [$];
  
  int num_choices = 20;
  int num_chosen = 5;
  
  function new();
  endfunction
  
  constraint choices_size_c { choices.size() == num_choices; }
  
  constraint chosen_c {
    chosen.size() == num_chosen;
    foreach (chosen[i]) {
      // check chosen[i] exists somewhere within choices
    }
  }
  
endclass

The idea is we have a number of valid choices that, for example, get programmed somewhere. Then we choose 5 of those valid choices for testing. Can this be done with constraints, or do I need to do this manually post-randomization?

dave_59 · Accepted Answer · 2022-10-12 04:40:26Z

1

Use the set membership operator inside

 constraint chosen_c {
    chosen.size() == num_chosen;
    foreach (chosen[i]) {
       chosen[i] inside {choices};
    }
  }

You can also add unique constraints to prevent repetition if that is a requirement you failed to mention

constraint uniq {
     unique {choices};
     unique {chosen};
}

edited Oct 12, 2022 at 4:40

answered Oct 12, 2022 at 2:17

dave_59

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