Initial try to support a variety of byte sizes for cuckoofilter.

Using generics, allowing to switch transparently between uint8 and
uint16 for the fingerprint size.

Performance neutral according to benchmarks

~/goworkspace/bin/benchstat ~/master.benchstats ~/generics.benchstats
name             old time/op  new time/op  delta
Filter_Reset-4   10.0µs ± 0%   9.9µs ± 0%   ~     (p=1.000 n=1+1)
Filter_Insert-4  18.2µs ± 0%  18.0µs ± 0%   ~     (p=1.000 n=1+1)
Filter_Lookup-4  1.52µs ± 0%  1.51µs ± 0%   ~     (p=1.000 n=1+1)

bucket.go

@@ -5,22 +5,21 @@ import (
 	"fmt"
 )
 
-// fingerprint represents a single entry in a bucket.
-type fingerprint uint16
+type fingerprintsize interface {
+	uint8 | uint16 | uint32
+}
 
 // bucket keeps track of fingerprints hashing to the same index.
-type bucket [bucketSize]fingerprint
+type bucket[T fingerprintsize] [bucketSize]T
 
 const (
-	nullFp              = 0
-	bucketSize          = 4
-	fingerprintSizeBits = 16
-	maxFingerprint      = (1 << fingerprintSizeBits) - 1
+	nullFp     = 0
+	bucketSize = 4
 )
 
 // insert a fingerprint into a bucket. Returns true if there was enough space and insertion succeeded.
 // Note it allows inserting the same fingerprint multiple times.
-func (b *bucket) insert(fp fingerprint) bool {
+func (b *bucket[T]) insert(fp T) bool {
 	for i, tfp := range b {
 		if tfp == nullFp {
 			b[i] = fp
@@ -32,7 +31,7 @@ func (b *bucket) insert(fp fingerprint) bool {
 
 // delete a fingerprint from a bucket.
 // Returns true if the fingerprint was present and successfully removed.
-func (b *bucket) delete(fp fingerprint) bool {
+func (b *bucket[T]) delete(fp T) bool {
 	for i, tfp := range b {
 		if tfp == fp {
 			b[i] = nullFp
@@ -42,7 +41,7 @@ func (b *bucket) delete(fp fingerprint) bool {
 	return false
 }
 
-func (b *bucket) contains(needle fingerprint) bool {
+func (b *bucket[T]) contains(needle T) bool {
 	for _, fp := range b {
 		if fp == needle {
 			return true
@@ -52,13 +51,13 @@ func (b *bucket) contains(needle fingerprint) bool {
 }
 
 // reset deletes all fingerprints in the bucket.
-func (b *bucket) reset() {
+func (b *bucket[T]) reset() {
 	for i := range b {
 		b[i] = nullFp
 	}
 }
 
-func (b *bucket) String() string {
+func (b *bucket[T]) String() string {
 	var buf bytes.Buffer
 	buf.WriteString("[")
 	for _, by := range b {

bucket_test.go

@@ -6,13 +6,13 @@ import (
 )
 
 func TestBucket_Reset(t *testing.T) {
-	var bkt bucket
-	for i := fingerprint(0); i < bucketSize; i++ {
+	var bkt bucket[uint16]
+	for i := uint16(0); i < bucketSize; i++ {
 		bkt[i] = i
 	}
 	bkt.reset()
 
-	var want bucket
+	var want bucket[uint16]
 	if !reflect.DeepEqual(bkt, want) {
 		t.Errorf("bucket.reset() got %v, want %v", bkt, want)
 	}

cuckoofilter.go

@@ -11,37 +11,56 @@ import (
 const maxCuckooKickouts = 500
 
 // Filter is a probabilistic counter.
-type Filter struct {
-	buckets []bucket
-	count   uint
+type Filter[T fingerprintsize] struct {
+	buckets        []bucket[T]
+	getFingerprint func(hash uint64) T
+	count          uint
 	// Bit mask set to len(buckets) - 1. As len(buckets) is always a power of 2,
 	// applying this mask mimics the operation x % len(buckets).
 	bucketIndexMask uint
 }
 
-// NewFilter returns a new cuckoofilter suitable for the given number of elements.
-// When inserting more elements, insertion speed will drop significantly and insertions might fail altogether.
-// A capacity of 1000000 is a normal default, which allocates
-// about ~2MB on 64-bit machines.
-func NewFilter(numElements uint) *Filter {
+func numBuckets(numElements uint) uint {
 	numBuckets := getNextPow2(uint64(numElements / bucketSize))
 	if float64(numElements)/float64(numBuckets*bucketSize) > 0.96 {
 		numBuckets <<= 1
 	}
 	if numBuckets == 0 {
 		numBuckets = 1
 	}
-	buckets := make([]bucket, numBuckets)
-	return &Filter{
+	return numBuckets
+}
+
+// NewFilter returns a new cuckoofilter suitable for the given number of elements.
+// When inserting more elements, insertion speed will drop significantly and insertions might fail altogether.
+// A capacity of 1000000 is a normal default, which allocates
+// about ~2MB on 64-bit machines.
+func NewFilter(numElements uint) *Filter[uint16] {
+	buckets := make([]bucket[uint16], numBuckets(numElements))
+	return &Filter[uint16]{
+		buckets:         buckets,
+		count:           0,
+		bucketIndexMask: uint(len(buckets) - 1),
+		getFingerprint:  getFinterprintUint16,
+	}
+}
+
+// NewFilterLowPrecision is the same as NewFilter, but returns a filter that uses
+// half the memory but has lower precision.
+func NewFilterLowPrecision(numElements uint) *Filter[uint8] {
+	buckets := make([]bucket[uint8], numBuckets(numElements))
+	return &Filter[uint8]{
 		buckets:         buckets,
 		count:           0,
 		bucketIndexMask: uint(len(buckets) - 1),
+		getFingerprint:  getFinterprintUint8,
 	}
 }
 
+
 // Lookup returns true if data is in the filter.
-func (cf *Filter) Lookup(data []byte) bool {
-	i1, fp := getIndexAndFingerprint(data, cf.bucketIndexMask)
+func (cf *Filter[T]) Lookup(data []byte) bool {
+	i1, fp := getIndexAndFingerprint(data, cf.bucketIndexMask, cf.getFingerprint)
 	if b := cf.buckets[i1]; b.contains(fp) {
 		return true
 	}
@@ -51,7 +70,7 @@ func (cf *Filter) Lookup(data []byte) bool {
 }
 
 // Reset removes all items from the filter, setting count to 0.
-func (cf *Filter) Reset() {
+func (cf *Filter[T]) Reset() {
 	for i := range cf.buckets {
 		cf.buckets[i].reset()
 	}
@@ -62,8 +81,8 @@ func (cf *Filter) Reset() {
 // * Might return false negatives
 // * Deletes are not guaranteed to work
 // To increase success rate of inserts, create a larger filter.
-func (cf *Filter) Insert(data []byte) bool {
-	i1, fp := getIndexAndFingerprint(data, cf.bucketIndexMask)
+func (cf *Filter[T]) Insert(data []byte) bool {
+	i1, fp := getIndexAndFingerprint(data, cf.bucketIndexMask, cf.getFingerprint)
 	if cf.insert(fp, i1) {
 		return true
 	}
@@ -74,15 +93,15 @@ func (cf *Filter) Insert(data []byte) bool {
 	return cf.reinsert(fp, randi(i1, i2))
 }
 
-func (cf *Filter) insert(fp fingerprint, i uint) bool {
+func (cf *Filter[T]) insert(fp T, i uint) bool {
 	if cf.buckets[i].insert(fp) {
 		cf.count++
 		return true
 	}
 	return false
 }
 
-func (cf *Filter) reinsert(fp fingerprint, i uint) bool {
+func (cf *Filter[T]) reinsert(fp T, i uint) bool {
 	for k := 0; k < maxCuckooKickouts; k++ {
 		j := rand.Intn(bucketSize)
 		// Swap fingerprint with bucket entry.
@@ -98,13 +117,13 @@ func (cf *Filter) reinsert(fp fingerprint, i uint) bool {
 }
 
 // Delete data from the filter. Returns true if the data was found and deleted.
-func (cf *Filter) Delete(data []byte) bool {
-	i1, fp := getIndexAndFingerprint(data, cf.bucketIndexMask)
+func (cf *Filter[T]) Delete(data []byte) bool {
+	i1, fp := getIndexAndFingerprint(data, cf.bucketIndexMask, cf.getFingerprint)
 	i2 := getAltIndex(fp, i1, cf.bucketIndexMask)
 	return cf.delete(fp, i1) || cf.delete(fp, i2)
 }
 
-func (cf *Filter) delete(fp fingerprint, i uint) bool {
+func (cf *Filter[T]) delete(fp T, i uint) bool {
 	if cf.buckets[i].delete(fp) {
 		cf.count--
 		return true
@@ -113,19 +132,20 @@ func (cf *Filter) delete(fp fingerprint, i uint) bool {
 }
 
 // Count returns the number of items in the filter.
-func (cf *Filter) Count() uint {
+func (cf *Filter[T]) Count() uint {
 	return cf.count
 }
 
 // LoadFactor returns the fraction slots that are occupied.
-func (cf *Filter) LoadFactor() float64 {
+func (cf *Filter[T]) LoadFactor() float64 {
 	return float64(cf.count) / float64(len(cf.buckets)*bucketSize)
 }
 
-const bytesPerBucket = bucketSize * fingerprintSizeBits / 8
+// TODO(panmari): Size of fingerprint needs to be derived from type. Currently hardcoded to 16 for uint16.
+const bytesPerBucket = bucketSize * 16 / 8
 
 // Encode returns a byte slice representing a Cuckoofilter.
-func (cf *Filter) Encode() []byte {
+func (cf *Filter[T]) Encode() []byte {
 	bytes := make([]byte, 0, len(cf.buckets)*bytesPerBucket)
 	for _, b := range cf.buckets {
 		for _, f := range b {
@@ -138,7 +158,7 @@ func (cf *Filter) Encode() []byte {
 }
 
 // Decode returns a Cuckoofilter from a byte slice created using Encode.
-func Decode(bytes []byte) (*Filter, error) {
+func Decode(bytes []byte) (*Filter[uint16], error) {
 	if len(bytes)%bucketSize != 0 {
 		return nil, fmt.Errorf("bytes must to be multiple of %d, got %d", bucketSize, len(bytes))
 	}
@@ -150,21 +170,22 @@ func Decode(bytes []byte) (*Filter, error) {
 		return nil, fmt.Errorf("numBuckets must to be a power of 2, got %d", numBuckets)
 	}
 	var count uint
-	buckets := make([]bucket, numBuckets)
+	buckets := make([]bucket[uint16], numBuckets)
 	for i, b := range buckets {
 		for j := range b {
 			var next []byte
 			next, bytes = bytes[:2], bytes[2:]
 
-			if fp := fingerprint(binary.LittleEndian.Uint16(next)); fp != 0 {
+			if fp := binary.LittleEndian.Uint16(next); fp != 0 {
 				buckets[i][j] = fp
 				count++
 			}
 		}
 	}
-	return &Filter{
+	return &Filter[uint16]{
 		buckets:         buckets,
 		count:           count,
 		bucketIndexMask: uint(len(buckets) - 1),
+		getFingerprint:  getFinterprintUint16,
 	}, nil
 }

cuckoofilter_test.go

@@ -7,10 +7,10 @@ import (
 	"io"
 	"math"
 	"os"
-	"reflect"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
 )
 
 // optFloatNear considers float64 as equal if the relative delta is small.
@@ -231,7 +231,9 @@ func TestEncodeDecode(t *testing.T) {
 	if err != nil {
 		t.Errorf("Expected no error, got %v", err)
 	}
-	if !reflect.DeepEqual(cf, got) {
+	if !cmp.Equal(cf, got,
+		cmp.AllowUnexported(Filter[uint16]{}),
+		cmpopts.IgnoreFields(Filter[uint16]{}, "getFingerprint")) {
 		t.Errorf("Decode = %v, want %v, encoded = %v", got, cf, encoded)
 	}
 }

example_threadsafe_test.go

@@ -9,7 +9,7 @@ import (
 
 // Small wrapper around cuckoo filter making it thread safe.
 type threadSafeFilter struct {
-	cf *cuckoo.Filter
+	cf *cuckoo.Filter[uint16]
 	mu sync.RWMutex
 }
 

go.mod

@@ -1,8 +1,10 @@
 module github.com/panmari/cuckoofilter
 
-go 1.15
+go 1.18
 
 require (
-	github.com/dgryski/go-metro v0.0.0-20200812162917-85c65e2d0165
+	github.com/dgryski/go-metro v0.0.0-20211015221634-2661b20a2446
 	github.com/google/go-cmp v0.5.2
 )
+
+require golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 // indirect

go.sum

@@ -1,5 +1,6 @@
-github.com/dgryski/go-metro v0.0.0-20200812162917-85c65e2d0165 h1:BS21ZUJ/B5X2UVUbczfmdWH7GapPWAhxcMsDnjJTU1E=
-github.com/dgryski/go-metro v0.0.0-20200812162917-85c65e2d0165/go.mod h1:c9O8+fpSOX1DM8cPNSkX/qsBWdkD4yd2dpciOWQjpBw=
+github.com/dgryski/go-metro v0.0.0-20211015221634-2661b20a2446 h1:QnWGyQI3H080vbC9E4jlr6scOYEnALtvV/69oATYzOo=
+github.com/dgryski/go-metro v0.0.0-20211015221634-2661b20a2446/go.mod h1:c9O8+fpSOX1DM8cPNSkX/qsBWdkD4yd2dpciOWQjpBw=
 github.com/google/go-cmp v0.5.2 h1:X2ev0eStA3AbceY54o37/0PQ/UWqKEiiO2dKL5OPaFM=
 github.com/google/go-cmp v0.5.2/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=

util.go

@@ -15,23 +15,35 @@ func randi(i1, i2 uint) uint {
 	return i2
 }
 
-func getAltIndex(fp fingerprint, i uint, bucketIndexMask uint) uint {
+func getAltIndex[T fingerprintsize](fp T, i uint, bucketIndexMask uint) uint {
 	b := make([]byte, 2)
 	binary.LittleEndian.PutUint16(b, uint16(fp))
 	hash := uint(metro.Hash64(b, 1337))
 	return (i ^ hash) & bucketIndexMask
 }
 
-func getFingerprint(hash uint64) fingerprint {
+func getFinterprintUint16(hash uint64) uint16 {
+	const fingerprintSizeBits = 16
+	const maxFingerprint = (1 << fingerprintSizeBits) - 1
 	// Use most significant bits for fingerprint.
 	shifted := hash >> (64 - fingerprintSizeBits)
 	// Valid fingerprints are in range [1, maxFingerprint], leaving 0 as the special empty state.
 	fp := shifted%(maxFingerprint-1) + 1
-	return fingerprint(fp)
+	return uint16(fp)
+}
+
+func getFinterprintUint8(hash uint64) uint8 {
+	const fingerprintSizeBits = 8
+	const maxFingerprint = (1 << fingerprintSizeBits) - 1
+	// Use most significant bits for fingerprint.
+	shifted := hash >> (64 - fingerprintSizeBits)
+	// Valid fingerprints are in range [1, maxFingerprint], leaving 0 as the special empty state.
+	fp := shifted%(maxFingerprint-1) + 1
+	return uint8(fp)
 }
 
 // getIndexAndFingerprint returns the primary bucket index and fingerprint to be used
-func getIndexAndFingerprint(data []byte, bucketIndexMask uint) (uint, fingerprint) {
+func getIndexAndFingerprint[T fingerprintsize](data []byte, bucketIndexMask uint, getFingerprint func(uint64) T) (uint, T) {
 	hash := metro.Hash64(data, 1337)
 	f := getFingerprint(hash)
 	// Use least significant bits for deriving index.

util_test.go

@@ -7,7 +7,9 @@ import (
 func TestIndexAndFP(t *testing.T) {
 	data := []byte("seif")
 	numBuckets := uint(1024)
-	i1, fp := getIndexAndFingerprint(data, numBuckets)
+	i1, fp := getIndexAndFingerprint(data, numBuckets, func(in uint64) uint16 {
+		return 2
+	})
 	i2 := getAltIndex(fp, i1, numBuckets)
 	i11 := getAltIndex(fp, i2, numBuckets)
 	i22 := getAltIndex(fp, i1, numBuckets)