SystemVerilog Array Manipulation

There are many built-in methods in SystemVerilog to help in array searching and ordering.

Array manipulation methods simply iterate through the array elements and each element is used to evaluate the expression specified by the with clause. The iterator argument specifies a local variable that can be used within the with expression to refer to the current element in the iteration. If an argument is not provided, item is the name used by default.

Array Locator Methods

The with clause and expresison is mandatory for some of these methods and for some others its optional.

Mandatory 'with' clause

These methods are used to filter out certain elements from an existing array based on a given expression. All such elements that satisfy the given expression is put into an array and returned. Hence the with clause is mandatory for the following methods.

module tb;
  int array[9] = '{4, 7, 2, 5, 7, 1, 6, 3, 1};
  int res[$];
  
  initial begin
    res = array.find(x) with (x > 3);
    $display ("find(x)         : %p", res);
    
    res = array.find_index with (item == 4);
    $display ("find_index      : res[%0d] = 4", res[0]);
    
    res = array.find_first with (item < 5 & item >= 3);
    $display ("find_first      : %p", res);
    
    res = array.find_first_index(x) with (x > 5);
    $display ("find_first_index: %p", res);
    
    res = array.find_last with (item <= 7 & item > 3);
    $display ("find_last       : %p", res);
    
    res = array.find_last_index(x) with (x < 3);
    $display ("find_last_index : %p", res);
  end
endmodule

ncsim> run
find(x)         : '{4, 7, 5, 7, 6}
find_index      : res[0] = 4
find_first      : '{4}
find_first_index: '{1}
find_last       : '{6}
find_last_index : '{8}
ncsim: *W,RNQUIE: Simulation is complete.

Optional 'with' clause

module tb;
  int array[9] = '{4, 7, 2, 5, 7, 1, 6, 3, 1};
  int res[$];
  
  initial begin   
    res = array.min();
    $display ("min          : %p", res);
    
    res = array.max();
    $display ("max          : %p", res);
    
    res = array.unique();
    $display ("unique       : %p", res);
    
    res = array.unique(x) with (x < 3);
    $display ("unique       : %p", res);
    
    res = array.unique_index;
    $display ("unique_index : %p", res);
  end
endmodule

ncsim> run
min          : '{1}
max          : '{7}
unique       : '{4, 7, 2, 5, 1, 6, 3}
unique       : '{4, 2}
unique_index : '{0, 1, 2, 3, 5, 6, 7}
ncsim: *W,RNQUIE: Simulation is complete.

Array Ordering Methods

These methods operate and alter the array directly.

Example

module tb;
  int array[9] = '{4, 7, 2, 5, 7, 1, 6, 3, 1};
  
  initial begin   
    array.reverse();
    $display ("reverse  : %p", array);
    
    array.sort();
    $display ("sort     : %p", array);
    
    array.rsort();
    $display ("rsort    : %p", array);
    
    for (int i = 0; i < 5; i++) begin
    	array.shuffle();
      $display ("shuffle Iter:%0d  = %p", i, array);
    end
  end
endmodule

ncsim> run
reverse  : '{1, 3, 6, 1, 7, 5, 2, 7, 4}
sort     : '{1, 1, 2, 3, 4, 5, 6, 7, 7}
rsort    : '{7, 7, 6, 5, 4, 3, 2, 1, 1}
shuffle Iter:0  = '{6, 7, 1, 7, 3, 2, 1, 4, 5}
shuffle Iter:1  = '{5, 1, 3, 4, 2, 7, 1, 7, 6}
shuffle Iter:2  = '{3, 1, 7, 4, 6, 7, 1, 2, 5}
shuffle Iter:3  = '{6, 4, 7, 3, 1, 7, 5, 2, 1}
shuffle Iter:4  = '{3, 6, 2, 5, 4, 7, 7, 1, 1}
ncsim: *W,RNQUIE: Simulation is complete.

Using array ordering on classes

class Register;
  string name;
  rand bit [3:0] rank;
  rand bit [3:0] pages;
  
  function new (string name);
    this.name = name;
  endfunction
  
  function void print();
    $display("name=%s rank=%0d pages=%0d", name, rank, pages);
  endfunction
  
endclass

module tb;
  Register rt[4];
  string name_arr[4] = '{"alexa", "siri", "google home", "cortana"};
  
  initial begin
    $display ("
-------- Initial Values --------");
    foreach (rt[i]) begin
      rt[i] = new (name_arr[i]);
      rt[i].randomize();
      rt[i].print();
    end
    
    $display ("
--------- Sort by name ------------");
    
    rt.sort(x) with (x.name);
    foreach (rt[i]) rt[i].print();
    
    $display ("
--------- Sort by rank, pages -----------");
    
    rt.sort(x) with ( {x.rank, x.pages});
    foreach (rt[i]) rt[i].print();
  end
endmodule

ncsim> run

-------- Initial Values --------
name=alexa rank=12 pages=13
name=siri rank=6 pages=12
name=google home rank=12 pages=13
name=cortana rank=7 pages=11

--------- Sort by name ------------
name=alexa rank=12 pages=13
name=cortana rank=7 pages=11
name=google home rank=12 pages=13
name=siri rank=6 pages=12

--------- Sort by rank, pages -----------
name=siri rank=6 pages=12
name=cortana rank=7 pages=11
name=alexa rank=12 pages=13
name=google home rank=12 pages=13
ncsim: *W,RNQUIE: Simulation is complete.

Array Reduction Methods

module tb;
  int array[4] = '{1, 2, 3, 4};
  int res[$];
  
  initial begin
    $display ("sum     = %0d", array.sum());    
    $display ("product = %0d", array.product());    
    $display ("and     = 0x%0h", array.and());
    $display ("or      = 0x%0h", array.or());    
    $display ("xor     = 0x%0h", array.xor());   
  end
endmodule

ncsim> run
sum     = 10
product = 24
and     = 0x0
or      = 0x7
xor     = 0x4
ncsim: *W,RNQUIE: Simulation is complete.