Random number distribution

SystemVerilog
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3

In reply to dave_59:

Hi Dave, I randomized the array 100 times, and when I saw the value for the sum its always 50 or 510. Can you explain why the sum is only 50 or 510?


// This is the class that we will randomize.
class my_item;
 
  rand bit [2:0] rand_val;
  rand bit[3:0] arr[];

  // Randomization constraints.
  constraint c {

    arr.size()==510;
    arr.sum with (int'(item)) dist {[1:50]:/90,[51:510]:/10};
    //rand_val dist {0:/10 , 1 :/ 45 , 2 :/ 45};
  }
  
  // Print out the items.
  function void print();
    //$display("rand_val: %0d", rand_val);
    $display("arr_sum: %0d", arr.sum with (int'(item)));
  endfunction
  
endclass

module automatic test;
  
  function void run;
    my_item item = new();
    for (int i = 0; i < 200; i++) begin
      item.randomize();
      item.print();
    end
    
  endfunction
  
  initial run();
  
endmodule