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/**
* At the moment, this is a partial hashmap implementation, not yet fit for
* use, but useful as a stress test for rustboot.
*/
type hashfn[K] = fn(&K) -> uint;
type eqfn[K] = fn(&K, &K) -> bool;
abs state type hashmap[K, V] = state obj {
fn size() -> uint;
fn insert(&K key, &V val) -> bool;
fn contains_key(&K key) -> bool;
fn get(&K key) -> V;
fn find(&K key) -> option.t[V];
fn remove(&K key) -> option.t[V];
fn rehash();
iter items() -> @tup(K,V);
};
fn mk_hashmap[K, V](&hashfn[K] hasher, &eqfn[K] eqer) -> hashmap[K, V] {
let uint initial_capacity = 32u; // 2^5
let util.rational load_factor = rec(num=3, den=4);
tag bucket[K, V] {
nil;
deleted;
some(K, V);
}
fn make_buckets[K, V](uint nbkts) -> vec[mutable bucket[K, V]] {
ret _vec.init_elt_mut[bucket[K, V]](nil[K, V], nbkts);
}
// Derive two hash functions from the one given by taking the upper
// half and lower half of the uint bits. Our bucket probing
// sequence is then defined by
//
// hash(key, i) := hashl(key) + i * hashr(key) for i = 0, 1, 2, ...
//
// Tearing the hash function apart this way is kosher in practice
// as, assuming 32-bit uints, the table would have to be at 2^32
// buckets before the resulting pair of hash functions no longer
// probes all buckets for a fixed key. Note that hashr is made to
// output odd numbers (hence coprime to the number of nbkts, which
// is always a power of 2), so that all buckets are probed for a
// fixed key.
fn hashl[K](&hashfn[K] hasher, uint nbkts, &K key) -> uint {
ret (hasher(key) >>> (sys.rustrt.size_of[uint]() * 8u / 2u));
}
fn hashr[K](&hashfn[K] hasher, uint nbkts, &K key) -> uint {
ret ((((~ 0u) >>> (sys.rustrt.size_of[uint]() * 8u / 2u))
& hasher(key)) * 2u + 1u);
}
fn hash[K](&hashfn[K] hasher, uint nbkts, &K key, uint i) -> uint {
ret (hashl[K](hasher, nbkts, key)
+ i * hashr[K](hasher, nbkts, key)) % nbkts;
}
/**
* We attempt to never call this with a full table. If we do, it
* will fail.
*/
impure fn insert_common[K, V](&hashfn[K] hasher,
&eqfn[K] eqer,
vec[mutable bucket[K, V]] bkts,
uint nbkts,
&K key,
&V val)
-> bool
{
let uint i = 0u;
while (i < nbkts) {
let uint j = hash[K](hasher, nbkts, key, i);
alt (bkts.(j)) {
case (some[K, V](?k, _)) {
if (eqer(key, k)) {
bkts.(j) = some[K, V](k, val);
ret false;
}
i += 1u;
}
case (_) {
bkts.(j) = some[K, V](key, val);
ret true;
}
}
}
fail; // full table
}
fn find_common[K, V](&hashfn[K] hasher,
&eqfn[K] eqer,
vec[mutable bucket[K, V]] bkts,
uint nbkts,
&K key)
-> option.t[V]
{
let uint i = 0u;
while (i < nbkts) {
let uint j = (hash[K](hasher, nbkts, key, i));
alt (bkts.(j)) {
case (some[K, V](?k, ?v)) {
if (eqer(key, k)) {
ret option.some[V](v);
}
}
case (nil[K, V]) {
ret option.none[V];
}
case (deleted[K, V]) { }
}
i += 1u;
}
ret option.none[V];
}
impure fn rehash[K, V](&hashfn[K] hasher,
&eqfn[K] eqer,
vec[mutable bucket[K, V]] oldbkts, uint noldbkts,
vec[mutable bucket[K, V]] newbkts, uint nnewbkts)
{
for (bucket[K, V] b in oldbkts) {
alt (b) {
case (some[K, V](?k, ?v)) {
insert_common[K, V](hasher, eqer, newbkts,
nnewbkts, k, v);
}
case (_) { }
}
}
}
state obj hashmap[K, V](hashfn[K] hasher,
eqfn[K] eqer,
mutable vec[mutable bucket[K, V]] bkts,
mutable uint nbkts,
mutable uint nelts,
util.rational lf)
{
fn size() -> uint { ret nelts; }
fn insert(&K key, &V val) -> bool {
let util.rational load = rec(num=(nelts + 1u) as int,
den=nbkts as int);
if (!util.rational_leq(load, lf)) {
let uint nnewbkts = _uint.next_power_of_two(nbkts + 1u);
let vec[mutable bucket[K, V]] newbkts =
make_buckets[K, V](nnewbkts);
rehash[K, V](hasher, eqer, bkts, nbkts,
newbkts, nnewbkts);
bkts = newbkts;
nbkts = nnewbkts;
}
if (insert_common[K, V](hasher, eqer, bkts,
nbkts, key, val)) {
nelts += 1u;
ret true;
}
ret false;
}
fn contains_key(&K key) -> bool {
alt (find_common[K, V](hasher, eqer, bkts, nbkts, key)) {
case (option.some[V](_)) { ret true; }
case (_) { ret false; }
}
fail; // FIXME: remove me when exhaustiveness checking works
}
fn get(&K key) -> V {
alt (find_common[K, V](hasher, eqer, bkts, nbkts, key)) {
case (option.some[V](?val)) { ret val; }
case (_) { fail; }
}
fail; // FIXME: remove me when exhaustiveness checking works
}
fn find(&K key) -> option.t[V] {
// FIXME: should be 'be' but parametric tail-calls don't
// work at the moment.
ret find_common[K, V](hasher, eqer, bkts, nbkts, key);
}
fn remove(&K key) -> option.t[V] {
let uint i = 0u;
while (i < nbkts) {
let uint j = (hash[K](hasher, nbkts, key, i));
alt (bkts.(j)) {
case (some[K, V](?k, ?v)) {
if (eqer(key, k)) {
bkts.(j) = deleted[K, V];
nelts -= 1u;
ret option.some[V](v);
}
}
case (deleted[K, V]) { }
case (nil[K, V]) {
ret option.none[V];
}
}
i += 1u;
}
ret option.none[V];
}
fn rehash() {
let vec[mutable bucket[K, V]] newbkts =
make_buckets[K, V](nbkts);
rehash[K, V](hasher, eqer, bkts, nbkts, newbkts, nbkts);
bkts = newbkts;
}
iter items() -> @tup(K,V) {
for (bucket[K,V] b in bkts) {
alt (b) {
case(some[K,V](?k,?v)) {
put @tup(k,v);
}
case (_) { }
}
}
}
}
let vec[mutable bucket[K, V]] bkts =
make_buckets[K, V](initial_capacity);
ret hashmap[K, V](hasher, eqer, bkts, initial_capacity, 0u, load_factor);
}
// Local Variables:
// mode: rust;
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// compile-command: "make -k -C .. 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
// End:
|
