bucket.go

@@ -22,11 +22,19 @@ func (b bucket[K, V]) location(key K) uint64 {
 }
 
 func (b bucket[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 *bucket[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) {
@@ -45,6 +53,10 @@ func (b *bucket[K, V]) resize(capacity uint64) {
 }
 
 func (b bucket[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) {
@@ -56,6 +68,10 @@ func (b bucket[K, V]) update(key K, value V) (updated bool) {
 }
 
 func (b *bucket[K, V]) evict(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 {

cuckoo_fuzz_test.go

@@ -1,12 +1,11 @@
 package cuckoo_test
 
 import (
-	"bytes"
-	"encoding/binary"
 	"maps"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	go_fuzz_utils "github.com/trailofbits/go-fuzz-utils"
 
 	"git.maximhutz.com/tools/go-cuckoo"
 )
@@ -20,49 +19,60 @@ func offsetHash(seed uint32) cuckoo.Hash[uint32] {
 	}
 }
 
+type fuzzStep struct {
+	drop       bool
+	key, value uint32
+}
+
+type fuzzScenario struct {
+	seedA, seedB uint32
+	steps        []fuzzStep
+}
+
 func FuzzInsertLookup(f *testing.F) {
-	f.Fuzz(func(t *testing.T, data []byte, seedA, seedB uint32) {
+	f.Fuzz(func(t *testing.T, data []byte) {
+		var scenario fuzzScenario
 		assert := assert.New(t)
 
+		if tp, err := go_fuzz_utils.NewTypeProvider(data); err != nil {
+			return
+		} else if err := tp.Fill(&scenario); err != nil {
+			return
+		}
+
+		if scenario.seedA == scenario.seedB {
+			return
+		}
+
 		actual := cuckoo.NewCustomTable[uint32, uint32](
-			offsetHash(seedA),
+			offsetHash(scenario.seedA),
-			offsetHash(seedB),
+			offsetHash(scenario.seedB),
 			func(a, b uint32) bool { return a == b },
 		)
 
 		expected := map[uint32]uint32{}
 
-		if seedA == seedB {
+		for _, step := range scenario.steps {
-			return
+			if step.drop {
-		}
+				err := actual.Drop(step.key)
-
-		r := bytes.NewReader(data)
-		var key, value uint32
-		var drop bool
-		for binary.Read(r, binary.LittleEndian, &key) == nil &&
-			binary.Read(r, binary.LittleEndian, &value) == nil {
-
-			if drop {
-				err := actual.Drop(key)
 				assert.NoError(err)
 
-				delete(expected, key)
+				delete(expected, step.key)
 
-				_, err = actual.Get(key)
+				_, err = actual.Get(step.key)
 				assert.Error(err)
 			} else {
-				err := actual.Put(key, value)
+				err := actual.Put(step.key, step.value)
 				assert.NoError(err)
 
-				expected[key] = value
+				expected[step.key] = step.value
 
-				found, err := actual.Get(key)
+				found, err := actual.Get(step.key)
 				assert.NoError(err)
-				assert.Equal(value, found)
+				assert.Equal(step.value, found)
 			}
-			assert.Equal(expected, maps.Collect(actual.Entries()))
 
-			drop = !drop
+			assert.Equal(expected, maps.Collect(actual.Entries()))
 		}
 	})
 }

go.mod

@@ -7,5 +7,6 @@ require github.com/stretchr/testify v1.11.1
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/trailofbits/go-fuzz-utils v0.0.0-20260318143407-0907cafe7589
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

go.sum

@@ -4,6 +4,8 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
+github.com/trailofbits/go-fuzz-utils v0.0.0-20260318143407-0907cafe7589 h1:UmBZCTPdDYore2IEHN+U4eIqEaRq6METh9pKiPumkqc=
+github.com/trailofbits/go-fuzz-utils v0.0.0-20260318143407-0907cafe7589/go.mod h1:zh+T+w9XT/3o4E0WLEGCdmLJ8Yqx/zY3o538tQY3OjY=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

table.go

@@ -28,7 +28,7 @@ func (t Table[K, V]) Size() int {
 }
 
 func log2(n uint64) (m int) {
-	return bits.Len64(n) - 1
+	return max(0, bits.Len64(n)-1)
 }
 
 func (t Table[K, V]) maxEvictions() int {
@@ -36,6 +36,12 @@ func (t Table[K, V]) maxEvictions() int {
 }
 
 func (t Table[K, V]) load() float64 {
+	// When there are no slots in the table, we still treat the load as 100%.
+	// Every slot in the table is full.
+	if t.TotalCapacity() == 0 {
+		return 1.0
+	}
+
 	return float64(t.Size()) / float64(t.TotalCapacity())
 }
 
@@ -57,6 +63,22 @@ func (t *Table[K, V]) resize(capacity uint64) error {
 	return nil
 }
 
+func (t *Table[K, V]) grow() error {
+	var newCapacity uint64
+
+	if t.TotalCapacity() == 0 {
+		newCapacity = 1
+	} else {
+		newCapacity = t.bucketA.capacity * t.growthFactor
+	}
+
+	return t.resize(newCapacity)
+}
+
+func (t *Table[K, V]) shrink() error {
+	return t.resize(t.bucketA.capacity / t.growthFactor)
+}
+
 // Get fetches the value for a key in the [Table]. Returns an error if no value
 // is found.
 func (t Table[K, V]) Get(key K) (value V, err error) {
@@ -102,7 +124,7 @@ func (t *Table[K, V]) Put(key K, value V) (err error) {
 		return fmt.Errorf("bad hash: resize on load %d/%d = %f", t.Size(), t.TotalCapacity(), t.load())
 	}
 
-	if err := t.resize(t.growthFactor * t.bucketA.capacity); err != nil {
+	if err := t.grow(); err != nil {
 		return err
 	}
 
@@ -116,7 +138,7 @@ func (t *Table[K, V]) Drop(key K) (err error) {
 	t.bucketB.drop(key)
 
 	if t.load() < t.minLoadFactor {
-		return t.resize(t.bucketA.capacity / t.growthFactor)
+		return t.shrink()
 	}
 
 	return nil

testdata/fuzz/FuzzInsertLookup/663e746d1518e2f5

@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("B000000000000001000000000000000000000000000000000000000000000000000000000000000000000000000000000")

testdata/fuzz/FuzzInsertLookup/7753b9a0c9a15ea7

@@ -1,4 +0,0 @@
-go test fuzz v1
-[]byte("00000000000000000000000000000000000000000000000000000000000000000000000000000000")
-uint32(51)
-uint32(38)