go-cuckoo/subtable.go

package cuckoo

// An Entry is a key-value pair.
type Entry[K, V any] struct {
	Key   K
	Value V
}

type slot[K, V any] struct {
	Entry[K, V]
	occupied bool
}

type subtable[K, V any] struct {
	hash           Hash[K]
	slots          []slot[K, V]
	capacity, size uint64
	compare        EqualFunc[K]
}

// location determines where in the bucket a certain key would be placed. If the
// capacity is 0, this will panic.
func (b *subtable[K, V]) location(key K) uint64 {
	return b.hash(key) % b.capacity
}

func (b *subtable[K, V]) get(key K) (value V, found bool) {
	if b.capacity == 0 {
		return
	}

	slot := b.slots[b.location(key)]
	return slot.Value, slot.occupied && b.compare(slot.Key, key)
}

func (b *subtable[K, V]) drop(key K) (occupied bool) {
	if b.capacity == 0 {
		return
	}

	slot := &b.slots[b.location(key)]

	if slot.occupied && b.compare(slot.Key, key) {
		slot.occupied = false
		b.size--
		return true
	}

	return false
}

func (b *subtable[K, V]) resized(capacity uint64) *subtable[K, V] {
	return &subtable[K, V]{
		slots:    make([]slot[K, V], capacity),
		capacity: capacity,
		hash:     b.hash,
		compare:  b.compare,
	}
}

func (b *subtable[K, V]) update(key K, value V) (updated bool) {
	if b.capacity == 0 {
		return
	}

	slot := &b.slots[b.location(key)]

	if slot.occupied && b.compare(slot.Key, key) {
		slot.Value = value
		return true
	}

	return false
}

func (b *subtable[K, V]) insert(insertion Entry[K, V]) (evicted Entry[K, V], eviction bool) {
	if b.capacity == 0 {
		return insertion, true
	}

	slot := &b.slots[b.location(insertion.Key)]

	if !slot.occupied {
		slot.Entry = insertion
		slot.occupied = true
		b.size++
		return
	}

	if b.compare(slot.Key, insertion.Key) {
		slot.Value = insertion.Value
		return
	}

	insertion, slot.Entry = slot.Entry, insertion
	return insertion, true
}

func newSubtable[K, V any](capacity uint64, hash Hash[K], compare EqualFunc[K]) *subtable[K, V] {
	return &subtable[K, V]{
		hash:     hash,
		capacity: capacity,
		compare:  compare,
		size:     0,
		slots:    make([]slot[K, V], capacity),
	}
}