pack buckets into uint64

Author: paulwe

bucket.go

@@ -3,16 +3,16 @@ package cuckoo
 import (
 	"bytes"
 	"fmt"
+	"math/bits"
 )
 
 // fingerprint represents a single entry in a bucket.
 type fingerprint uint16
 
 // bucket keeps track of fingerprints hashing to the same index.
-type bucket [bucketSize]fingerprint
+type bucket uint64
 
 const (
-	nullFp              = 0
 	bucketSize          = 4
 	fingerprintSizeBits = 16
 	maxFingerprint      = (1 << fingerprintSizeBits) - 1
@@ -21,8 +21,8 @@ const (
 // 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 {
-	if i := b.index(nullFp); i != 4 {
-		b[i] = fp
+	if i := findZeros(uint64(*b)); i != 0 {
+		*b |= bucket(fp) << ((bits.Len64(i)/fingerprintSizeBits - 1) * fingerprintSizeBits)
 		return true
 	}
 	return false
@@ -31,43 +31,37 @@ 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 {
-	if i := b.index(fp); i != 4 {
-		b[i] = nullFp
+	if i := findValue(uint64(*b), uint16(fp)); i != 0 {
+		*b &= ^(maxFingerprint << ((bits.Len64(i)/fingerprintSizeBits - 1) * fingerprintSizeBits))
 		return true
 	}
 	return false
 }
 
+func (b *bucket) swap(i uint64, fp fingerprint) fingerprint {
+	p := (*b) >> (i * fingerprintSizeBits) & maxFingerprint
+	*b = (*b) & ^(maxFingerprint<<(i*fingerprintSizeBits)) | (bucket(fp) << (i * fingerprintSizeBits))
+	return fingerprint(p)
+}
+
 func (b *bucket) contains(needle fingerprint) bool {
-	return b.index(needle) != 4
+	return findValue(uint64(*b), uint16(needle)) != 0
 }
 
-func (b *bucket) index(needle fingerprint) uint8 {
-	if b[0] == needle {
-		return 0
-	}
-	if b[1] == needle {
-		return 1
-	}
-	if b[2] == needle {
-		return 2
-	}
-	if b[3] == needle {
-		return 3
-	}
-	return 4
+func (b *bucket) nullsCount() uint {
+	return uint(bits.OnesCount64(findZeros(uint64(*b))))
 }
 
 // reset deletes all fingerprints in the bucket.
 func (b *bucket) reset() {
-	*b = [bucketSize]fingerprint{nullFp, nullFp, nullFp, nullFp}
+	*b = 0
 }
 
 func (b *bucket) String() string {
 	var buf bytes.Buffer
 	buf.WriteString("[")
-	for _, by := range b {
-		buf.WriteString(fmt.Sprintf("%5d ", by))
+	for i := 3; i >= 0; i-- {
+		buf.WriteString(fmt.Sprintf("%5d ", ((*b)>>(i*fingerprintSizeBits))&maxFingerprint))
 	}
 	buf.WriteString("]")
 	return buf.String()

bucket_test.go

@@ -8,12 +8,65 @@ import (
 func TestBucket_Reset(t *testing.T) {
 	var bkt bucket
 	for i := fingerprint(0); i < bucketSize; i++ {
-		bkt[i] = i
+		bkt.insert(i + 1)
 	}
+
 	bkt.reset()
 
 	var want bucket
 	if !reflect.DeepEqual(bkt, want) {
 		t.Errorf("bucket.reset() got %v, want %v", bkt, want)
 	}
 }
+
+func TestBucket_Insert(t *testing.T) {
+	var bkt bucket
+	for i := fingerprint(0); i < bucketSize; i++ {
+		if !bkt.insert(i + 1) {
+			t.Error("bucket insert failed")
+		}
+	}
+	if bkt.insert(5) {
+		t.Error("expected bucket insert to fail after overflow")
+	}
+}
+
+func TestBucket_Delete(t *testing.T) {
+	var bkt bucket
+	for i := fingerprint(0); i < bucketSize; i++ {
+		bkt.insert(i + 1)
+	}
+
+	for i := fingerprint(0); i < bucketSize; i++ {
+		if !bkt.delete(i + 1) {
+			t.Error("bucket delete failed")
+		}
+		if !bkt.insert(i + 1) {
+			t.Error("bucket insert after delete failed")
+		}
+	}
+}
+
+func TestBucket_Swap(t *testing.T) {
+	var bkt bucket
+	bkt.insert(123)
+	if prev := bkt.swap(3, 321); prev != 123 {
+		t.Errorf("swap returned unexpected value %d", prev)
+	}
+	if !bkt.contains(321) {
+		t.Errorf("contains after swap failed")
+	}
+}
+
+func TestBucket_Contains(t *testing.T) {
+	var bkt bucket
+	for i := fingerprint(0); i < bucketSize; i++ {
+		bkt.insert(i + 1)
+	}
+
+	for i := fingerprint(0); i < bucketSize; i++ {
+		if !bkt.contains(i + 1) {
+			t.Error("bucket contains failed")
+		}
+	}
+}

cuckoofilter.go

@@ -37,7 +37,7 @@ func NewFilter(numElements uint) *Filter {
 	return &Filter{
 		buckets:         buckets,
 		count:           0,
-		bucketIndexMask: uint(len(buckets) - 1),
+		bucketIndexMask: numBuckets - 1,
 	}
 }
 
@@ -73,7 +73,11 @@ func (cf *Filter) Insert(data []byte) bool {
 	if cf.insert(fp, i2) {
 		return true
 	}
-	return cf.reinsert(fp, randi(&cf.rng, i1, i2))
+	if cf.rng.Uint64()&1 == 0 {
+		return cf.reinsert(fp, i1)
+	} else {
+		return cf.reinsert(fp, i2)
+	}
 }
 
 func (cf *Filter) insert(fp fingerprint, i uint) bool {
@@ -86,9 +90,9 @@ func (cf *Filter) insert(fp fingerprint, i uint) bool {
 
 func (cf *Filter) reinsert(fp fingerprint, i uint) bool {
 	for k := 0; k < maxCuckooKickouts; k++ {
-		j := cf.rng.Intn(bucketSize)
+		j := cf.rng.Uint64() & (bucketSize - 1)
 		// Swap fingerprint with bucket entry.
-		cf.buckets[i][j], fp = fp, cf.buckets[i][j]
+		fp = cf.buckets[i].swap(j, fp)
 
 		// Move kicked out fingerprint to alternate location.
 		i = getAltIndex(fp, i, cf.bucketIndexMask)
@@ -130,9 +134,7 @@ const bytesPerBucket = bucketSize * fingerprintSizeBits / 8
 func (cf *Filter) Encode() []byte {
 	buf := make([]byte, 0, len(cf.buckets)*bytesPerBucket)
 	for _, b := range cf.buckets {
-		for _, fp := range b {
-			buf = binary.LittleEndian.AppendUint16(buf, uint16(fp))
-		}
+		buf = binary.LittleEndian.AppendUint64(buf, uint64(b))
 	}
 	return buf
 }
@@ -152,14 +154,10 @@ func Decode(data []byte) (*Filter, error) {
 
 	var count, pos uint
 	buckets := make([]bucket, numBuckets)
-	for i, b := range buckets {
-		for j := range b {
-			buckets[i][j] = fingerprint(binary.LittleEndian.Uint16(data[pos : pos+2]))
-			pos += 2
-			if buckets[i][j] != nullFp {
-				count++
-			}
-		}
+	for i := range buckets {
+		buckets[i] = bucket(binary.LittleEndian.Uint64(data[pos : pos+8]))
+		pos += 8
+		count += bucketSize - buckets[i].nullsCount()
 	}
 	return &Filter{
 		buckets:         buckets,

util.go

@@ -4,7 +4,6 @@ import (
 	"encoding/binary"
 	"math/bits"
 
-	"github.com/zeebo/wyhash"
 	"github.com/zeebo/xxh3"
 )
 
@@ -14,18 +13,10 @@ func init() {
 	b := make([]byte, 2)
 	for i := 0; i < maxFingerprint+1; i++ {
 		binary.LittleEndian.PutUint16(b, uint16(i))
-		altHash[i] = (uint(xxh3.Hash(b)))
+		altHash[i] = uint(xxh3.Hash(b))
 	}
 }
 
-// randi returns either i1 or i2 randomly.
-func randi(rng *wyhash.RNG, i1, i2 uint) uint {
-	if rng.Uint64()&1 == 0 {
-		return i1
-	}
-	return i2
-}
-
 func getAltIndex(fp fingerprint, i uint, bucketIndexMask uint) uint {
 	return (i ^ altHash[fp]) & bucketIndexMask
 }
@@ -50,3 +41,13 @@ func getIndexAndFingerprint(data []byte, bucketIndexMask uint) (uint, fingerprin
 func getNextPow2(n uint64) uint {
 	return uint(1 << bits.Len64(n-1))
 }
+
+// SEE: https://graphics.stanford.edu/~seander/bithacks.html#ZeroInWord
+func findZeros(v uint64) uint64 {
+	return ^((((v & 0x7FFF7FFF7FFF7FFF) + 0x7FFF7FFF7FFF7FFF) | v) | 0x7FFF7FFF7FFF7FFF)
+}
+
+// SEE: https://graphics.stanford.edu/~seander/bithacks.html#ValueInWord
+func findValue(x uint64, n uint16) uint64 {
+	return findZeros(x ^ (^uint64(0) / (1<<16 - 1) * uint64(n)))
+}