How to get same hits for equally Weighted Distribution?

SystemVerilog
1

dear All,
i trying to understand the dist constraints for weighted distribution.
i thought that dist will help me in assigning equal dist (equal hits for each value) but the fact is that the total hits “approximately” equal as shown in the below histogram results. so i need to know how can i force the simulation to hit equally for each value, and how many repeats value to get that results.

code:

class Weighted;
  rand int val;
  constraint c_dist {val dist {1:= 1, 2:= 1, 3:= 1, 5:= 1, 8:= 1};}
endclass

module testclass;
Weighted w;

initial begin
  int count[9], maxx[$];
  w = new();
  repeat (2000) begin
  assert(w.randomize());
  count[w.val]++; // Count the number of hits
  end
  maxx = count.max(); // Get largest value in count
// Print histogram of count
$display(count.max);
foreach(count[i])
  if (count[i]) begin  
  $write("count[%0d]=%5d ", i, count[i]);
  repeat (count[i]*40/maxx[0]) $write("*");
  $display;
end
end
endmodule

results:

count[1]= 427 ****************************************

count[2]= 399 *************************************

count[3]= 391 ************************************

count[5]= 403 *************************************

count[8]= 380 ***********************************

thanks in advance.

2

In reply to moustafaali:

As you approach an infinite number of repeats, the count will approach an equally infinite number of counts.

The only way to force an equal number of hits is to use the randc modifier. That cycles through the all values 1,2,3,5 and 8 in a random order and then repeats the values in a different random order.

3

In reply to dave_59:

excellent, thanks a lot

count[1]= 400 ****************************************

count[2]= 400 ****************************************

count[3]= 400 ****************************************

count[5]= 400 ****************************************

count[8]= 400 ****************************************