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sv array method sum()

arjuny

 Hi,

    I was going through the "sv for verification". I am trying to run the examples given in the book on IUS(9.2).

    As per LRM (array reduction methods),"sum() returns the sum of all the array elements or, if a with clause is specified, returns the sum of the values yielded by evaluating the expression for each array element." 

    But the following code generates values "0"(if item > 3) or "1"(if item > 2) when i tried to run the following example.

    As per my understanding with LRM, if (item > 3 ) the output should be "9" and if (item > 2) the output should be "12".

module test;
  bit[7:0] dyn[]='{1,2,3,4,5},cnt;
  initial begin
    foreach(dyn[i]) begin
      $display("dyn[%0d]=%0d",i,dyn[i]);
    end
    //check website
    //cnt = dyn.sum() with (item > 3); //returns "0"
    cnt = dyn.sum() with (item > 2); //returns "1"
    $display("dyn : %d",cnt);
  end
endmodule


How the tools is generating output "0" or "1"?

 Thanks & Regards,

Arjun.

  • Hi Arjun, As i know .sum() method is not safe to use.. Whatever expression you are giving as per the LRM it will result in the following expression like : For dyn.sum() with(item >3) will result in cnt = (1>3) + (2>3) + (3>3) + (4>3) + (5>3) And i am not sure what will be the output of this expression.

  • Explanation on values "0"(if item > 3) :

    cnt = (1>3) + (2>3) + (3>3) + (4>3) + (5>3) = F+F+F+T+T=0+0+0+1+1=single bit 0

    Explanation on values "1"(if item > 2) :

    cnt = (1>2) + (2>2) + (3>2) + (4>2) + (5>2) = F+F+T+T+T=0+0+1+1+1=single bit 1

    To get output  "9"  for  (item > 3 ) , rewrite the code as : 

    cnt = dyn.sum() with ((item > 3)?item:0)  //returns "9"

    To get output  "12"  for  (item > 2 ) , rewrite the code as : 

    cnt = dyn.sum() with ((item > 2)?item:0); //returns "12"

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