Different Array Types and Queues in System Verilog
Dynamic Array:
- Usage of dynamic array when user to allocate its size for storage during run time.
- Dynamic array store a contiguous collection of data.
- The array indexing should be always integer type.
To allocate the size of a dynamic array, we have to use a new[] operator.
Example:
int dyn_arr [];
initial
begin
dyn_arr = new[10]; //Allocated 10 elements
end
How to resize a dynamic array?
Example:
initial
begin
dyn_arr = new[25](dyn_arr); //Resize the Array and Copy
end
Dynamic Array Methods:
- function int size()
- Returns the current size of the array
- function void delete()
- Empties array contents and zero-sizes it
int my_addr[ ] = new[256];
initial begin
$display("Size of my_addr = %0d", my_addr.size() );
my_addr.delete();
$display("Size of my_addr (after delete) = %0d", my_addr.size());
end
Associative Array:
- It is also allocated during run time.
- This is the array, user need when data is sparse.
- It is used when we don’t have to allocate contiguous collection of data, or data in a proper sequence or index.
- Indexing is not regular, can be accessed using indexing like integer or string type or any scalar.
Example:
bit i_array[*]; // associative array of bits (unspecified index)
// unspecified index (*) implies any integral value
bit [7:0] age [string]; // associative array of 8-bit vectors, indexed by string
initial
begin
string tom = “tom”;
age [tom] = 21;
age [“joe”] = 32;
$display("%s is %d years of age ", tom, age[tom], "[%0d ages available]", age.num());
end
Associative Array Methods:
- function int num()
- Returns the number of entries in the array, if empty returns 0
- function void delete( [input index] )
- Index is optional
- If index is specified, deletes the item at the specified index
- If index is not specified the all elements in the array are removed
- function int exists ( input index );
- Checks if an element exists at the specified index within the given array.
- Returns 1 if the element exists, otherwise it returns 0
- function int first( ref index )
- Assigns to the given index variable the value of the first (smallest) index in the associative array
- It returns 0 if the array is empty, and 1 otherwise
- function int last( ref index )
- Assigns to the given index variable the value of the last (largest) index in the associative array
- It returns 0 if the array is empty, and 1 otherwise.
- function int next( ref index );
- finds the entry whose index is greater than the given index. If there is a next entry, the index variable is assigned the index of the next entry, and the function returns 1
- Otherwise, index is unchanged, and the function returns 0
- function int prev( ref index );
- finds the entry whose index is smaller than the given index. If there is a previous entry, the index variable is assigned the index of the previous entry, and the function returns 1
- Otherwise, the index is unchanged, and the function returns 0
Queue:
- Queue is a variable size, ordered collection of Homogenous Data.
- It is flexible, as it is variable in size and analogous to an 1-dimensional Unpacked array that can shrink & grow automatically and can be of size zero.
- The main advantage of queue over dynamic array is that, we don’t need new[] operator to allocate storage space for a queue.
- The other advantages of queue over dynamic array is that we can manipulate the queue using various queue methods like: push, pop, delete, insert, size.
Example:
module test_example ;
int my_queue[$] = { 1, 2, 3 };
string s_queue [$] = {"first","second","third","fourth"};
string store;
initial
begin
// Use of the size() method/operator
$display("\n size() operator used");
for (int i = 0 ; i < my_queue.size(); i++ )
$display (my_queue[i]);
$display("\n\n Elements of s_queue is :");
for (int i = 0; i < s_queue.size; i++)
$write(s_queue[i]," ");
// Use of insert() method/operator
s_queue.insert(1,"next"); // Previous element 1 is now turned to element 2.
s_queue.insert(2,"somewhere");
$display("\n\n insert() operator used");
for (int i = 0; i < s_queue.size; i++)
$write(s_queue[i]," ");
// Use of delete() method/operator
s_queue.delete(1); // delete the element 1
s_queue.delete(3); // delete the element 3
$display("\n\n delete() operator used");
for (int i = 0; i < s_queue.size; i++)
$write(string_queue[i]," ");
// Use of pop_front() method/operator (it deletes the front of the queue)
store = s_queue.pop_front();
$display("\n\n pop_front() operator used");
$display(" %s",store);
for (int i = 0; i < s_queue.size; i++)
$write(s_queue[i]," ");
// Use of pop_back() method/operator (it deletes the back of the queue)
store= s_queue.pop_back();
$display("\n\n pop_back() operator used");
$display(" %s",store);
for (int i = 0; i < s_queue.size; i++)
$write(s_queue[i]," ");
// Use of push_front() and push_back() method/operator
s_queue.push_front("in-front");
s_queue.push_back("in-back");
$display("\n\n push_front() and push_back() operator used");
for (int i = 0; i < s_queue.size; i++)
$write(s_queue[i]," \n ");
end
endmodule
