Randomize dynamic array with unique values

SystemVerilog
, , , ,
1

I have been asked to randomize a dynamic array with unique values with following conditions

  1. Unique key word can’t be used
  2. Use pre and post randomize functions
  3. Can not use foreach or any other loops in constraint
2

In reply to bachan21:

class A;
  typedef bit [2:0] number_t;
  rand number_t number;
  number_t recent_numbers[$];
  bit add;
  
  function void post_randomize();
    add = 1;
    foreach (recent_numbers[i]) begin
      if (recent_numbers[i] == number) begin
        add = 0;
        break;
      end else begin
        add = 1;
      end
    end
    if (add == 1) begin
      recent_numbers.push_front(number);
    end
    if (recent_numbers.size() > 5)
       void'(recent_numbers.pop_back());
  endfunction
endclass : A


module top();
  A a = new();
  initial begin
    repeat(10) begin
    if(!a.randomize()) $display("Please look into randomization issue");
    if (a.recent_numbers.size() == 5) begin
      $display("recent_numbers = %p",a.recent_numbers);
    end
    end
  end

endmodule : top
3

In reply to megamind:

Hi,
Can you explain your code, because I cant find the declaration of any dynamic array

4

In reply to bachan21:

I have used queue , instead of dynamic array , if you use dynamic array then syntax will change for adding elements , nothing much in the logic should change. Does it make sense ?

5

In reply to megamind:

Actually it is better to use queue, to handle element addition.

6

In reply to megamind:

Yeah I got your logic.
You are randomizing the value and adding to the queue by randomizing for 10 times.
But can we modify the logic such that a dynamic array can be used instead of queue?

7

In reply to bachan21:

class A;

  typedef bit [2:0] number_t;
  number_t recent_numbers[];
  
  function void post_randomize();
    recent_numbers = new[5];
    foreach (recent_numbers[i]) begin
      recent_numbers[i] = i;
    end
  endfunction : post_randomize

endclass : A


module top();

  A a = new();

  initial begin
    repeat(1) begin
    if(!a.randomize()) $display("Please look into randomization issue");
      $display("----->> recent_numbers = %p \n",a.recent_numbers);
    end
  end

endmodule : top
8

In reply to megamind:

class A;

  typedef bit [31:0] number_t;
  number_t recent_numbers[];
  bit [16:0] random_num;
  
  function void post_randomize();
    recent_numbers = new[5];
    foreach (recent_numbers[i]) begin
      recent_numbers[i] = i;
    end
    recent_numbers.shuffle();
    random_num = $urandom();
    $display("random_num = %0d ",random_num);
    foreach (recent_numbers[i]) begin
      recent_numbers[i] = recent_numbers[i] + random_num;
    end
  endfunction : post_randomize

endclass : A


module top();

  A a = new();

  initial begin
    repeat(10) begin
    if(!a.randomize()) $display("Please look into randomization issue");
      $display(" >>> Recent_numbers = %p \n\n",a.recent_numbers);
    end
  end

endmodule : top
1 Like
9 
class packet;
  rand bit [4:0] valid[];
   constraint valid_c {
     valid.size() == 15;
   }
   function void post_randomize();
     bit [4:0] tmp;
     valid[0] = $random;
     for(int i=1; i<valid.size(); i=i+1) begin//{
       bit flag=0;
       while(flag==0) begin//{
         tmp = $random;
         for(int j=0; j<i; j++) begin//{
           if(tmp == valid[j] ) begin//{
              flag=0; break;
           end//}
            flag=1;
         end//}
       end//}
       valid[i] = tmp;
     end//}
   endfunction

endclass

module tb;
initial begin
packet pkt;
pkt = new();

$display("------------------------------------");
  if(!pkt.randomize()) $fatal(1, "Randomize Failed");
  foreach(pkt.valid[i]) $display("valid[%0d] = %d ", i, pkt.valid[i]);
$display("------------------------------------");

end
endmodule