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hyperloglog.go
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hyperloglog.go
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package hyperloglog
import (
"encoding/binary"
"errors"
"fmt"
"math"
"sort"
)
const (
pp = uint8(25)
mp = uint32(1) << pp
version = 2
)
type Sketch struct {
p uint8
m uint32
alpha float64
tmpSet *set
sparseList *compressedList
regs []uint8
}
func New() *Sketch { return New14() } // New returns a HyperLogLog Sketch with 2^14 registers (precision 14)
func New14() *Sketch { return newSketchNoError(14, true) } // New14 returns a HyperLogLog Sketch with 2^14 registers (precision 14)
func New16() *Sketch { return newSketchNoError(16, true) } // New16 returns a HyperLogLog Sketch with 2^16 registers (precision 16)
func NewNoSparse() *Sketch { return newSketchNoError(14, false) } // NewNoSparse returns a HyperLogLog Sketch with 2^14 registers (precision 14) that will not use a sparse representation
func New16NoSparse() *Sketch { return newSketchNoError(16, false) } // New16NoSparse returns a HyperLogLog Sketch with 2^16 registers (precision 16) that will not use a sparse representation
func newSketchNoError(precision uint8, sparse bool) *Sketch {
sk, _ := NewSketch(precision, sparse)
return sk
}
func NewSketch(precision uint8, sparse bool) (*Sketch, error) {
if precision < 4 || precision > 18 {
return nil, fmt.Errorf("p has to be >= 4 and <= 18")
}
m := uint32(1) << precision
s := &Sketch{
m: m,
p: precision,
alpha: alpha(float64(m)),
}
if sparse {
s.tmpSet = newSet(0)
s.sparseList = newCompressedList(0)
} else {
s.regs = make([]uint8, m)
}
return s, nil
}
func (sk *Sketch) sparse() bool { return sk.sparseList != nil }
// Clone returns a deep copy of sk.
func (sk *Sketch) Clone() *Sketch {
clone := *sk
clone.regs = append([]uint8(nil), sk.regs...)
clone.tmpSet = sk.tmpSet.Clone()
clone.sparseList = sk.sparseList.Clone()
return &clone
}
func (sk *Sketch) maybeToNormal() {
if uint32(sk.tmpSet.Len())*100 > sk.m {
sk.mergeSparse()
if uint32(sk.sparseList.Len()) > sk.m {
sk.toNormal()
}
}
}
func (sk *Sketch) Merge(other *Sketch) error {
if other == nil {
return nil
}
if sk.p != other.p {
return errors.New("precisions must be equal")
}
if sk.sparse() && other.sparse() {
sk.mergeSparseSketch(other)
} else {
sk.mergeDenseSketch(other)
}
return nil
}
func (sk *Sketch) mergeSparseSketch(other *Sketch) {
sk.tmpSet.Merge(other.tmpSet)
for iter := other.sparseList.Iter(); iter.HasNext(); {
sk.tmpSet.add(iter.Next())
}
sk.maybeToNormal()
}
func (sk *Sketch) mergeDenseSketch(other *Sketch) {
if sk.sparse() {
sk.toNormal()
}
if other.sparse() {
other.tmpSet.ForEach(func(k uint32) {
i, r := decodeHash(k, other.p, pp)
sk.insert(i, r)
})
for iter := other.sparseList.Iter(); iter.HasNext(); {
i, r := decodeHash(iter.Next(), other.p, pp)
sk.insert(i, r)
}
} else {
for i, v := range other.regs {
if v > sk.regs[i] {
sk.regs[i] = v
}
}
}
}
func (sk *Sketch) toNormal() {
if sk.tmpSet.Len() > 0 {
sk.mergeSparse()
}
sk.regs = make([]uint8, sk.m)
for iter := sk.sparseList.Iter(); iter.HasNext(); {
i, r := decodeHash(iter.Next(), sk.p, pp)
sk.insert(i, r)
}
sk.tmpSet = nil
sk.sparseList = nil
}
func (sk *Sketch) insert(i uint32, r uint8) { sk.regs[i] = max(r, sk.regs[i]) }
func (sk *Sketch) Insert(e []byte) { sk.InsertHash(hash(e)) }
func (sk *Sketch) InsertHash(x uint64) {
if sk.sparse() {
if sk.tmpSet.add(encodeHash(x, sk.p, pp)) {
sk.maybeToNormal()
}
return
}
i, r := getPosVal(x, sk.p)
sk.insert(uint32(i), r)
}
func (sk *Sketch) Estimate() uint64 {
if sk.sparse() {
sk.mergeSparse()
return uint64(linearCount(mp, mp-sk.sparseList.count))
}
sum, ez := sumAndZeros(sk.regs)
m := float64(sk.m)
est := sk.alpha * m * (m - ez) / (sum + beta(sk.p, ez))
return uint64(est + 0.5)
}
func (sk *Sketch) mergeSparse() {
if sk.tmpSet.Len() == 0 {
return
}
keys := make(uint64Slice, 0, sk.tmpSet.Len())
sk.tmpSet.ForEach(func(k uint32) {
keys = append(keys, k)
})
sort.Sort(keys)
newList := newCompressedList(4*sk.tmpSet.Len() + sk.sparseList.Len())
for iter, i := sk.sparseList.Iter(), 0; iter.HasNext() || i < len(keys); {
if !iter.HasNext() {
newList.Append(keys[i])
i++
continue
}
if i >= len(keys) {
newList.Append(iter.Next())
continue
}
x1, x2 := iter.Peek(), keys[i]
if x1 == x2 {
newList.Append(iter.Next())
i++
} else if x1 > x2 {
newList.Append(x2)
i++
} else {
newList.Append(iter.Next())
}
}
sk.sparseList = newList
sk.tmpSet = newSet(0)
}
// MarshalBinary implements the encoding.BinaryMarshaler interface.
func (sk *Sketch) MarshalBinary() (data []byte, err error) {
data = make([]byte, 0, 8+len(sk.regs))
// Marshal a version marker.
data = append(data, version)
// Marshal p.
data = append(data, sk.p)
// Marshal b
data = append(data, 0)
if sk.sparse() {
// It's using the sparse Sketch.
data = append(data, byte(1))
// Add the tmp_set
tsdata, err := sk.tmpSet.MarshalBinary()
if err != nil {
return nil, err
}
data = append(data, tsdata...)
// Add the sparse Sketch
sdata, err := sk.sparseList.MarshalBinary()
if err != nil {
return nil, err
}
return append(data, sdata...), nil
}
// It's using the dense Sketch.
data = append(data, byte(0))
// Add the dense sketch Sketch.
sz := len(sk.regs)
data = append(data, []byte{
byte(sz >> 24),
byte(sz >> 16),
byte(sz >> 8),
byte(sz),
}...)
// Marshal each element in the list.
for _, v := range sk.regs {
data = append(data, byte(v))
}
return data, nil
}
// ErrorTooShort is an error that UnmarshalBinary try to parse too short
// binary.
var ErrorTooShort = errors.New("too short binary")
// UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
func (sk *Sketch) UnmarshalBinary(data []byte) error {
if len(data) < 8 {
return ErrorTooShort
}
// Unmarshal version. We may need this in the future if we make
// non-compatible changes.
v := data[0]
// Unmarshal p.
p := data[1]
// Unmarshal b.
b := data[2]
// Determine if we need a sparse Sketch
sparse := data[3] == byte(1)
// Make a newSketch Sketch if the precision doesn't match or if the Sketch was used
if sk.p != p || sk.regs != nil || sk.tmpSet.Len() > 0 || (sk.sparseList != nil && sk.sparseList.Len() > 0) {
newh, err := NewSketch(p, sparse)
if err != nil {
return err
}
*sk = *newh
}
// h is now initialised with the correct p. We just need to fill the
// rest of the details out.
if sparse {
// Using the sparse Sketch.
// Unmarshal the tmp_set.
tssz := binary.BigEndian.Uint32(data[4:8])
sk.tmpSet = newSet(int(tssz))
// We need to unmarshal tssz values in total, and each value requires us
// to read 4 bytes.
tsLastByte := int((tssz * 4) + 8)
for i := 8; i < tsLastByte; i += 4 {
k := binary.BigEndian.Uint32(data[i : i+4])
sk.tmpSet.add(k)
}
// Unmarshal the sparse Sketch.
return sk.sparseList.UnmarshalBinary(data[tsLastByte:])
}
// Using the dense Sketch.
sk.sparseList = nil
sk.tmpSet = nil
if v == 1 {
return sk.unmarshalBinaryV1(data[8:], b)
}
return sk.unmarshalBinaryV2(data)
}
func sumAndZeros(regs []uint8) (res, ez float64) {
for _, v := range regs {
if v == 0 {
ez++
}
res += 1.0 / math.Pow(2.0, float64(v))
}
return res, ez
}
func (sk *Sketch) unmarshalBinaryV1(data []byte, b uint8) error {
sk.regs = make([]uint8, len(data)*2)
for i, v := range data {
sk.regs[i*2] = uint8((v >> 4)) + b
sk.regs[i*2+1] = uint8((v<<4)>>4) + b
}
return nil
}
func (sk *Sketch) unmarshalBinaryV2(data []byte) error {
sk.regs = data[8:]
return nil
}