Unrolled linked list

An unrolled linked list is a linear data structure that is a variant on the linked list. Instead of just storing 1 element at each node, unrolled linked lists store an entire array at each node.

Unrolled linked lists combine the advantages of the array (small memory overhead) with the benefits of linked lists (fast insertion and deletion) to produce vastly better performance. By storing multiple elements at each node, unrolled linked lists effectively spread out the overhead of linked lists across multiple elements. So, if an unrolled linked list stores an array of 4 elements at each node, its spreading the linked list overhead (pointers) across those 4 elements.

The true benefits of the unrolled linked list come in the form of caching. The unrolled linked list takes advantage of this when it comes to indexing.

How to use

The dependency can be found as following: unrolled-linked-list = 1.0.1

Example:

use unrolled_linked_list::UnrolledLinkedList;

fn main(){
  let mut list = UnrolledLinkedList::new();
  list.insert(0, 1);
  list.push(2);
  list.push(3);
  list.insert(3,4);
  if let Some(four) =  list.pop() { println!(" should be {}", four)}
  
  let one_opt = list.get(0);
  let one_mut_opt = list.get_mut(0);

  list.remove(0);  

  for el in list.iter(){
    println!("elem {}",el);
  }    
 
}

Comparison with linked list and vec

For the details, see the folder benches. The numbers and results have the typical format for the library criterion.

The typical result example:

Benchmarking push/unrolled_linked_list
Benchmarking push/unrolled_linked_list: Warming up for 3.0000 s
Benchmarking push/unrolled_linked_list: Collecting 100 samples in estimated 5.0358 s (364k iterations)
Benchmarking push/unrolled_linked_list: Analyzing
push/unrolled_linked_list
                        time:   [14.078 us 14.776 us 15.527 us]
                        change: [+3.9244% +7.5033% +11.271%] (p = 0.00 < 0.05)
                        Performance has regressed.

Operation	Description	unrolled ll	vec	ll
push	insert 100 elements to the end	14.7	12.3	25.8
pop	retrieve 100 elements from the end	20.6	12.1	20.6
insert	insert 100 elements to the beginning	11.9	12.7	20.2
insert_middle	insert 100 elements to the middle	14.0	13.1	22.8(absent, was replaced to push)
get	insert 100 elements to the middle	16.6	13.1	27.7(absent, was replaced to push)
remove	remove the third part of elements	17.8	15.8	24.3
iter	iter through the collection	17.9	12.8	24.8
iter_mut	mut iter through the collection	22.6	30.4	33.2
into_iter	iter with possession through the collection	21.6	12.9	25.8