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//! A hashmap implementation.
//! TODO: we will need function pointers/closures if we want to make the map
//! generic in the key type.
use std::vec::Vec;
pub type Key = usize; // TODO: make this generic
pub type Hash = usize;
pub enum List<T> {
Cons(Key, T, Box<List<T>>),
Nil,
}
/// A hash function for the keys.
/// Rk.: we use shared references because we anticipate on the generic
/// hash map version.
pub fn hash_key(k: &Key) -> Hash {
// Do nothing for now, we might want to implement something smarter
// in the future
*k
}
/// A hash map from [u64] to values
pub struct HashMap<T> {
/// The current number of values in the table
num_values: usize,
/// The max load factor, expressed as a fraction
max_load_factor: (usize, usize),
/// The table itself
slots: Vec<List<T>>,
}
impl<T> HashMap<T> {
/// Allocate a vector of slots of a given size.
/// We would need a loop, but can't use loops for now...
fn allocate_slots(mut slots: Vec<List<T>>, n: usize) -> Vec<List<T>> {
if n == 0 {
slots
} else {
slots.push(List::Nil);
HashMap::allocate_slots(slots, n - 1)
}
}
pub fn new() -> Self {
let slots = HashMap::allocate_slots(Vec::new(), 32);
HashMap {
num_values: 0,
max_load_factor: (4, 5),
slots,
}
}
/// We need a loop here too...
/// Also, we start with the end, so that F* sees that the function terminates.
fn clear_slots(slots: &mut Vec<List<T>>, i: usize) {
if i > 0 {
let i = i - 1;
slots[i] = List::Nil;
HashMap::clear_slots(slots, i)
} else {
()
}
}
pub fn clear(&mut self) {
self.num_values = 0;
let len = self.slots.len();
HashMap::clear_slots(&mut self.slots, len);
}
pub fn len(&self) -> usize {
self.num_values
}
fn insert_in_list(key: Key, value: T, ls: &mut List<T>) {
match ls {
List::Nil => *ls = List::Cons(key, value, Box::new(List::Nil)),
List::Cons(ckey, cvalue, ls) => {
if *ckey == key {
*cvalue = value;
} else {
HashMap::insert_in_list(key, value, ls)
}
}
}
}
pub fn insert(&mut self, key: Key, value: T) {
let hash = hash_key(&key);
let hash_mod = hash % self.slots.len();
HashMap::insert_in_list(key, value, self.slots.get_mut(hash_mod).unwrap());
}
fn get_in_list<'l, 'k>(key: &'k Key, ls: &'l List<T>) -> Option<&'l T> {
match ls {
List::Nil => None,
List::Cons(ckey, cvalue, ls) => {
if ckey == key {
Some(cvalue)
} else {
HashMap::get_in_list(key, ls)
}
}
}
}
/// The signature is not exactly the same as the one in
/// [https://doc.rust-lang.org/std/collections/struct.HashMap.html#method.get_mut]
/// (the region paramaters are more precise here).
pub fn get<'l, 'k>(&'l self, key: &'k Key) -> Option<&'l T> {
let hash = hash_key(key);
let hash_mod = hash % self.slots.len();
HashMap::get_in_list(key, self.slots.get(hash_mod).unwrap())
}
fn get_mut_in_list<'l, 'k>(key: &'k Key, ls: &'l mut List<T>) -> Option<&'l mut T> {
match ls {
List::Nil => None,
List::Cons(ckey, cvalue, ls) => {
if ckey == key {
Some(cvalue)
} else {
HashMap::get_mut_in_list(key, ls)
}
}
}
}
/// Same remark as for [get].
pub fn get_mut<'l, 'k>(&'l mut self, key: &'k Key) -> Option<&'l mut T> {
let hash = hash_key(key);
let hash_mod = hash % self.slots.len();
HashMap::get_mut_in_list(key, self.slots.get_mut(hash_mod).unwrap())
}
fn remove_from_list(key: &Key, ls: &mut List<T>) -> Option<T> {
match ls {
List::Nil => None,
List::Cons(ckey, cvalue, tl) => {
if ckey == key {
// We have to move under borrows, so we need to use
// [std::mem::replace] in several steps.
// Retrieve the tail
let mv_ls = std::mem::replace(ls, List::Nil);
match mv_ls {
List::Nil => unreachable!(),
List::Cons(_, cvalue, tl) => {
// Make the list equal to its tail
*ls = *tl;
// Returned the dropped value
Some(cvalue)
}
}
} else {
HashMap::remove_from_list(key, tl)
}
}
}
}
/// Same remark as for [get].
pub fn remove(&mut self, key: &Key) -> Option<T> {
let hash = hash_key(key);
let hash_mod = hash % self.slots.len();
HashMap::remove_from_list(key, self.slots.get_mut(hash_mod).unwrap())
}
}
#[test]
fn test1() {
let mut hm: HashMap<u64> = HashMap::new();
hm.insert(0, 42);
hm.insert(128, 18);
hm.insert(1024, 138);
hm.insert(1056, 256);
assert!(*hm.get(&128).unwrap() == 18);
let x = hm.get_mut(&1024).unwrap();
*x = 56;
assert!(*hm.get(&1024).unwrap() == 56);
assert!(hm.get(&10).is_none());
let x = hm.remove(&1024).unwrap();
assert!(x == 56);
assert!(*hm.get(&0).unwrap() == 42);
assert!(*hm.get(&128).unwrap() == 18);
assert!(*hm.get(&1056).unwrap() == 256);
}
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