9 Associative Arrays +1

A continuing introduction to associative arrays, reviewing setting default values and using some built-in methods (exists(), first(), next()).

If a non-initialized index is read the default value for the data type will be returned.
A default may be specified in the structure literal which is used to initialize the associative array.

bc. integer aa [bit [15:0]];
aa = '{2:5, 6:55, 7:3, 16'hFFFE:-6, default:0};

Some methods that can be used for traversing associative arrays.

//returns 1 if it element at index exists, else 0
function int exists(input index);

//returns 1 if it there is a first index (i.e. any existent index means there is a first), else 0
//sets index to the value of the first element (where first is the smallest index)
function int first(ref index);

//returns 1 if it there is a next index (where the next index is greater than value of index when function is called, i.e. passed in as the ref index), else 0
//updates index to the value of the next element
function int next(ref index);

//returns 1 if it there is a previous index (less than the passed in ref index), else 0
//updates index to the value of the previous element (next smallest index, starting from the input ref index)
function int prev(ref index);

//returns 1 if it there is a last index (i.e. any existent index means there is a last), else 0
//sets index to the value of the last element (where last is the largest index)
function int last(ref index);

example code

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
module aa;
   integer aa [bit [15:0]];
   bit [15:0] ii,iii;      

   initial begin
      aa  = '{2:5, 6:55, 7:3, 16'hFFFE:-6, default:0};
      show();
      $display(" >>%0d",aa[88]);
      show();
      if (aa.exists(6)) begin
     aa[6]  = 6;
     show();
      end // if (aa.exists(6))
      // first, last, next, prev
      if (aa.first(ii)) begin
     void'(aa.next(iii));
     void'(aa.next(iii));
     $display(" aa[%0d]=%0d, aa[%0d]=%0d", ii, aa[ii], iii, aa[iii]);
     aa[ii]  = aa[iii];  
     show();     
      end
   end

   function void show();
      foreach (aa[i]) begin
     $write("aa[%4h]=%0d, ",i,aa[i]);    
      end
      $display("");   
      $display(" aa size =%0d",aa.size());      
   endfunction   

endmodule // aa

.
//run command

1
irun -sv aa.sv

NOTA BENE: See Comments section for an explanation of my mistake in using next() in two consecutive calls to reach the second value.