Definitions

   The factorial of   0   (zero)   is defined as being   1   (unity).
   The   Factorial Function   of a positive integer,    n,    is defined as the product of the sequence:
                 n,   n-1,   n-2,   ...   1 



Task

Write a function to return the factorial of a number.

Solutions can be iterative or recursive.

Support for trapping negative    n    errors is optional.



Related task

   Primorial numbers


module main;
 
  function automatic [7:0] factorial;
    input [7:0] i_Num; 
    begin
      if (i_Num == 1)
        factorial = 1; 
      else
        factorial = i_Num * factorial(i_Num-1);
    end
  endfunction
 
  initial
    begin
      $display("Factorial of 1 = %d", factorial(1));
      $display("Factorial of 2 = %d", factorial(2));
      $display("Factorial of 3 = %d", factorial(3));
      $display("Factorial of 4 = %d", factorial(4));
      $display("Factorial of 5 = %d", factorial(5));
    end
endmodule