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Merged
sunshowers merged 6 commits into from
May 22, 2026
Merged

for hash tables, cache hash with index #257

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ae0497a
[spr] initial version
sunshowers May 22, 2026
7b2f487
typo
sunshowers May 22, 2026
490d37e
switch to a unit test
sunshowers May 22, 2026
8bac9dd
rename module
sunshowers May 22, 2026
f96a9e7
fix cfg()
sunshowers May 22, 2026
fb71745
rustfmt
sunshowers May 22, 2026
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1 change: 1 addition & 0 deletions crates/iddqd/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@ proptest = { workspace = true, optional = true }

[dev-dependencies]
expectorate.workspace = true
foldhash.workspace = true
iddqd-test-utils.workspace = true
proptest.workspace = true
serde.workspace = true
Expand Down
46 changes: 13 additions & 33 deletions crates/iddqd/src/bi_hash_map/imp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,9 +11,10 @@ use crate::{
internal::{ValidateCompact, ValidationError},
support::{
ItemIndex,
alloc::{AllocWrapper, Allocator, Global, global_alloc},
alloc::{Allocator, Global, global_alloc},
borrow::DormantMutRef,
fmt_utils::StrDisplayAsDebug,
hash_table,
item_set::ItemSet,
map_hash::MapHash,
},
Expand All @@ -24,7 +25,6 @@ use core::{
hash::{BuildHasher, Hash},
};
use equivalent::Equivalent;
use hashbrown::hash_table;

/// A 1:1 (bijective) map for two keys and a value.
///
Expand Down Expand Up @@ -759,14 +759,8 @@ impl<T: BiHashItem, S: Clone + BuildHasher, A: Allocator> BiHashMap<T, S, A> {
/// ```
pub fn reserve(&mut self, additional: usize) {
self.items.reserve(additional);
let items = &self.items;
let state = &self.tables.state;
self.tables
.k1_to_item
.reserve(additional, |ix| state.hash_one(items[*ix].key1()));
self.tables
.k2_to_item
.reserve(additional, |ix| state.hash_one(items[*ix].key2()));
self.tables.k1_to_item.reserve(additional);
self.tables.k2_to_item.reserve(additional);
}

/// Tries to reserve capacity for at least `additional` more elements to be
Expand Down Expand Up @@ -820,15 +814,13 @@ impl<T: BiHashItem, S: Clone + BuildHasher, A: Allocator> BiHashMap<T, S, A> {
additional: usize,
) -> Result<(), crate::errors::TryReserveError> {
self.items.try_reserve(additional)?;
let items = &self.items;
let state = &self.tables.state;
self.tables
.k1_to_item
.try_reserve(additional, |ix| state.hash_one(items[*ix].key1()))
.try_reserve(additional)
.map_err(crate::errors::TryReserveError::from_hashbrown)?;
self.tables
.k2_to_item
.try_reserve(additional, |ix| state.hash_one(items[*ix].key2()))
.try_reserve(additional)
.map_err(crate::errors::TryReserveError::from_hashbrown)?;
Ok(())
}
Expand Down Expand Up @@ -875,14 +867,8 @@ impl<T: BiHashItem, S: Clone + BuildHasher, A: Allocator> BiHashMap<T, S, A> {
self.tables.k1_to_item.remap_indexes(&remap);
self.tables.k2_to_item.remap_indexes(&remap);
}
let items = &self.items;
let state = &self.tables.state;
self.tables
.k1_to_item
.shrink_to_fit(|ix| state.hash_one(items[*ix].key1()));
self.tables
.k2_to_item
.shrink_to_fit(|ix| state.hash_one(items[*ix].key2()));
self.tables.k1_to_item.shrink_to_fit();
self.tables.k2_to_item.shrink_to_fit();
}

/// Shrinks the capacity of the map with a lower limit. It will drop
Expand Down Expand Up @@ -932,14 +918,8 @@ impl<T: BiHashItem, S: Clone + BuildHasher, A: Allocator> BiHashMap<T, S, A> {
self.tables.k1_to_item.remap_indexes(&remap);
self.tables.k2_to_item.remap_indexes(&remap);
}
let items = &self.items;
let state = &self.tables.state;
self.tables
.k1_to_item
.shrink_to(min_capacity, |ix| state.hash_one(items[*ix].key1()));
self.tables
.k2_to_item
.shrink_to(min_capacity, |ix| state.hash_one(items[*ix].key2()));
self.tables.k1_to_item.shrink_to(min_capacity);
self.tables.k2_to_item.shrink_to(min_capacity);
}

/// Returns an iterator over all items in the map.
Expand Down Expand Up @@ -2436,13 +2416,13 @@ impl<T: BiHashItem + Eq, S: Clone + BuildHasher, A: Allocator> Eq
}

fn detect_dup_or_insert<'a, A: Allocator>(
item: hash_table::Entry<'a, ItemIndex, AllocWrapper<A>>,
item: hash_table::Entry<'a, A>,
duplicates: &mut BTreeSet<ItemIndex>,
) -> Option<hash_table::VacantEntry<'a, ItemIndex, AllocWrapper<A>>> {
) -> Option<hash_table::VacantEntry<'a, A>> {
match item {
hash_table::Entry::Vacant(slot) => Some(slot),
hash_table::Entry::Occupied(slot) => {
duplicates.insert(*slot.get());
duplicates.insert(slot.get());
None
}
}
Expand Down
106 changes: 86 additions & 20 deletions crates/iddqd/src/id_hash_map/imp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ use crate::{
ItemIndex,
alloc::{Allocator, Global, global_alloc},
borrow::DormantMutRef,
hash_table,
item_set::ItemSet,
map_hash::MapHash,
},
Expand All @@ -20,7 +21,6 @@ use core::{
hash::{BuildHasher, Hash},
};
use equivalent::Equivalent;
use hashbrown::hash_table;

/// A hash map where the key is part of the value.
///
Expand Down Expand Up @@ -642,11 +642,7 @@ impl<T: IdHashItem, S: Clone + BuildHasher, A: Allocator> IdHashMap<T, S, A> {
/// ```
pub fn reserve(&mut self, additional: usize) {
self.items.reserve(additional);
let items = &self.items;
let state = &self.tables.state;
self.tables
.key_to_item
.reserve(additional, |ix| state.hash_one(items[*ix].key()));
self.tables.key_to_item.reserve(additional);
}

/// Tries to reserve capacity for at least `additional` more elements to be
Expand Down Expand Up @@ -696,11 +692,9 @@ impl<T: IdHashItem, S: Clone + BuildHasher, A: Allocator> IdHashMap<T, S, A> {
additional: usize,
) -> Result<(), crate::errors::TryReserveError> {
self.items.try_reserve(additional)?;
let items = &self.items;
let state = &self.tables.state;
self.tables
.key_to_item
.try_reserve(additional, |ix| state.hash_one(items[*ix].key()))
.try_reserve(additional)
.map_err(crate::errors::TryReserveError::from_hashbrown)?;
Ok(())
}
Expand Down Expand Up @@ -742,11 +736,7 @@ impl<T: IdHashItem, S: Clone + BuildHasher, A: Allocator> IdHashMap<T, S, A> {
if !remap.is_identity() {
self.tables.key_to_item.remap_indexes(&remap);
}
let items = &self.items;
let state = &self.tables.state;
self.tables
.key_to_item
.shrink_to_fit(|ix| state.hash_one(items[*ix].key()));
self.tables.key_to_item.shrink_to_fit();
}

/// Shrinks the capacity of the map with a lower limit. It will drop
Expand Down Expand Up @@ -791,11 +781,7 @@ impl<T: IdHashItem, S: Clone + BuildHasher, A: Allocator> IdHashMap<T, S, A> {
if !remap.is_identity() {
self.tables.key_to_item.remap_indexes(&remap);
}
let items = &self.items;
let state = &self.tables.state;
self.tables
.key_to_item
.shrink_to(min_capacity, |ix| state.hash_one(items[*ix].key()));
self.tables.key_to_item.shrink_to(min_capacity);
}

/// Iterates over the items in the map.
Expand Down Expand Up @@ -1403,7 +1389,7 @@ impl<T: IdHashItem, S: Clone + BuildHasher, A: Allocator> IdHashMap<T, S, A> {
.entry(state, key, |index| self.items[index].key())
{
hash_table::Entry::Occupied(slot) => {
duplicates.insert(*slot.get());
duplicates.insert(slot.get());
None
}
hash_table::Entry::Vacant(slot) => Some(slot),
Expand Down Expand Up @@ -1789,3 +1775,83 @@ impl<T: IdHashItem, S: Default + Clone + BuildHasher, A: Allocator + Default>
map
}
}

#[cfg(all(test, feature = "std"))]
mod tests {
use super::*;
use core::{cell::Cell, hash::Hasher};

std::thread_local! {
static USER_HASH_CALLS: Cell<u32> = const { Cell::new(0) };
}

#[derive(Debug)]
struct CountedKey(u32);

impl Hash for CountedKey {
fn hash<H: Hasher>(&self, state: &mut H) {
USER_HASH_CALLS.with(|c| c.set(c.get() + 1));
self.0.hash(state);
}
}

impl PartialEq for CountedKey {
fn eq(&self, other: &Self) -> bool {
self.0 == other.0
}
}
impl Eq for CountedKey {}

#[derive(Debug)]
struct CountedItem {
id: u32,
}

impl IdHashItem for CountedItem {
type Key<'a> = CountedKey;
fn key(&self) -> Self::Key<'_> {
CountedKey(self.id)
}
id_upcast!();
}

// This is a unit test and not an integration test to ensure rehashing
// actually happens. (Rehashing is not externally observable in integration
// tests.)
#[test]
fn reserve_rehash_uses_cached_hash() {
let mut map = IdHashMap::<CountedItem, _>::with_hasher(
foldhash::fast::FixedState::with_seed(0),
);
// Insert items (legitimately calls user Hash).
for id in [
0u32, 17, 1, 12, 5, 21, 8, 10, 18, 4, 16, 22, 9, 24, 23, 13, 7, 25,
26, 20, 31, 11, 14, 2, 6,
] {
let _ = map.insert_overwrite(CountedItem { id });
}
// Drop most entries, leaving the table heavy with tombstones so the
// next reserve favors `rehash_in_place` over a fresh-allocation grow.
map.retain(|item| item.id % 2 == 1 && item.id % 3 != 0);

USER_HASH_CALLS.with(|c| c.set(0));
let rehash_calls = map.tables.key_to_item.reserve_counting_rehash(10);
let user_calls = USER_HASH_CALLS.with(Cell::get);

assert!(
rehash_calls > 0,
"expected reserve to invoke the rehash callback at least once \
(setup did not actually trigger a rehash; if hashbrown's \
growth/rehash heuristic changed, retune the constants)",
);
assert_eq!(
user_calls, 0,
"reserve must not invoke user `Hash` during rehash; got \
{user_calls} call(s) for {rehash_calls} rehash-callback \
invocation(s)",
);

map.validate(ValidateCompact::NonCompact)
.expect("map remains valid after reserve");
}
}
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