Unexpected Behaviour From Xilinx Vivado?

SystemVerilog
1

Hi,

I was trying to learn some array methods when I encountered a strange phenomena when trying calculate an array’s sum based on a iterator condition using a “with” clause

To give context, here’s the code

module tb_array_methods;
    function void disp_msg(input string tag, input string msg);
        $display($sformatf("[%0t][%0s]: %0s", $time, tag, msg));
    endfunction
    int arr[$] = {21,33,42,20,20,42,11,24,33};
    longint res;
    int arr_loc[$];
    int res_2;


    bit b_array[] = '{1,0,0,1,0,1};



    // ====================================== //
    // Array Locator Methods
    // All array locator methods return the results as a queue of type "int" and not "integer"
    initial begin



        // How about we combine some boolean functions with locators?
        //int arr[$] = {21,33,42,20,20,42,11,24,33};
        res_2 = arr.sum() with (item>34); 
        // Returns sum({0,0,1,0,0,1,0,0,0}) = 2; 
        // This can be used to find the count of certain values        
        disp_msg("Block 3", $sformatf("res_2 = %0d", res_2));


        res_2 = arr.sum() with (item * (item>34)); 
        // Returns sum({0,0,42,0,0,42,0,0,0}) = 84;


        res_2 = arr.sum() with (item > 34? item:0);
        // Returns 84
        disp_msg("Block 3", $sformatf("res_2 = %0d", res_2));
        
    end
endmodule

When I ran this code, I got this result

image

But I was expecting a sum of 2. Instead I got a 565641244.

Could anyone please tell me what’s wrong here?

Also when i use

res_2 = arr.sum(x) with (x>34);

I get

res_2 = 111067408

PS: I also noticed that Xilinx says compile issues when i use queues with product() and and(). Is that a xilinx issue? Because in chris spear, he uses them with queues

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image632×169 12 KB

2

The code you have shown does not match the output you’re getting. Your code only calls disp_msg() twice, yet your output looks like it was called five times. And we can’t help with your compile issues unless you show us the error messages.

res_2 = arr.sum(x) with (x>34);

Has a problem: the expression inside the with clause is a relational operator whose result is a single bit. So its output can only be 0 or 1. If you want a count of elements greater than 34, you would write:

res_2 = arr.sum(x) with (int'(x>34));