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 size of a dynamic array, we have to use 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

 

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