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Copy pathbloom.go
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210 lines (180 loc) · 5.87 KB
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/*
Package bloom provides data structures and methods for creating Bloom filters.
A Bloom filter is a representation of a set of _n_ items, where the main
requirement is to make membership queries; _i.e._, whether an item is a
member of a set.
A Bloom filter has two parameters: _m_, a maximum size (typically a reasonably large
multiple of the cardinality of the set to represent) and _k_, the number of hashing
functions on elements of the set. (The actual hashing functions are important, too,
but this is not a parameter for this implementation). A Bloom filter is backed by
a BitSet; a key is represented in the filter by setting the bits at each value of the
hashing functions (modulo _m_). Set membership is done by _testing_ whether the
bits at each value of the hashing functions (again, modulo _m_) are set. If so,
the item is in the set. If the item is actually in the set, a Bloom filter will
never fail (the true positive rate is 1.0); but it is susceptible to false
positives. The art is to choose _k_ and _m_ correctly.
In this implementation, the hashing functions used is murmurhash,
a non-cryptographic hashing function.
This implementation accepts keys for setting as testing as []byte. Thus, to
add a string item, "Love":
uint n = 1000
filter := bloom.New(20*n, 5) // load of 20, 5 keys
filter.Add([]byte("Love"))
Similarly, to test if "Love" is in bloom:
if filter.Test([]byte("Love"))
*/
package bloom
import (
"math"
"github.com/m3db/bitset"
)
func bloomFilterLocation(h [4]uint64, i, m uint64) uint {
v := h[i%2] + i*h[2+(((i+(i%2))%4)/2)]
return uint(v % m)
}
// BloomFilter is a bloom filter set membership.
// It cannot be concurrently read or written to. Multiple concurrent readers
// is also unsafe so a sync.Mutex must be used to guard read/write access if
// desired. This is due to a cached hash digest being used to avoid
// allocation each read/write.
type BloomFilter struct {
m uint64
k uint64
set *bitset.BitSet
}
// NewBloomFilter creates a new bloom filter that can represent
// m elements with k hashes. It is not concurrent read or write safe.
func NewBloomFilter(m uint, k uint) *BloomFilter {
if m < 1 {
m = 1
}
if k < 1 {
k = 1
}
return &BloomFilter{
m: uint64(m),
k: uint64(k),
set: bitset.NewBitSet(m),
}
}
// EstimateFalsePositiveRate estimates m and k, based on:
// https://stackoverflow.com/a/22467497
func EstimateFalsePositiveRate(n uint, p float64) (m uint, k uint) {
floatM := (float64(-1) * float64(n) * math.Log(p)) / (math.Pow(math.Log(2), 2))
floatK := (floatM / float64(n)) * math.Log(2)
m, k = uint(math.Ceil(floatM)), uint(math.Ceil(floatK))
return
}
// Add value to the set.
func (b *BloomFilter) Add(value []byte) {
h := sum128WithEntropy(value)
for i := uint64(0); i < b.k; i++ {
b.set.Set(bloomFilterLocation(h, i, b.m))
}
}
// Test if value is in the set.
func (b *BloomFilter) Test(value []byte) bool {
h := sum128WithEntropy(value)
for i := uint64(0); i < b.k; i++ {
if !b.set.Test(bloomFilterLocation(h, i, b.m)) {
return false
}
}
return true
}
// M returns the m elements represented.
func (b *BloomFilter) M() uint {
return uint(b.m)
}
// K returns the k hashes used.
func (b *BloomFilter) K() uint {
return uint(b.k)
}
// BitSet returns the bitset used.
func (b *BloomFilter) BitSet() *bitset.BitSet {
return b.set
}
// ReadOnlyBloomFilter is a read only bloom filter set membership.
// It cannot be concurrently read or written to. Multiple concurrent readers
// is also unsafe so a sync.Mutex must be used to guard read/write access if
// desired. This is due to a cached hash digest being used to avoid
// allocation each read/write.
type ReadOnlyBloomFilter struct {
m uint64
k uint64
set *bitset.ReadOnlyBitSet
}
// NewReadOnlyBloomFilter returns a new read only bloom filter backed
// by a byte slice, this means it can be used with a mmap'd bytes ref.
// It is not concurrent read or write safe.
func NewReadOnlyBloomFilter(m, k uint, data []byte) *ReadOnlyBloomFilter {
return &ReadOnlyBloomFilter{
m: uint64(m),
k: uint64(k),
set: bitset.NewReadOnlyBitSet(data),
}
}
// Test if value is in the set.
func (b *ReadOnlyBloomFilter) Test(value []byte) bool {
h := sum128WithEntropy(value)
for i := uint64(0); i < b.k; i++ {
if !b.set.Test(bloomFilterLocation(h, i, b.m)) {
return false
}
}
return true
}
// M returns the m elements represented.
func (b *ReadOnlyBloomFilter) M() uint {
return uint(b.m)
}
// K returns the k hashes used.
func (b *ReadOnlyBloomFilter) K() uint {
return uint(b.k)
}
// BitSet returns the bitset used.
func (b *ReadOnlyBloomFilter) BitSet() *bitset.ReadOnlyBitSet {
return b.set
}
// ConcurrentReadOnlyBloomFilter is a concurrent read only bloom filter set
// membership. It can be concurrently read from by any number of readers.
type ConcurrentReadOnlyBloomFilter struct {
m uint64
k uint64
set *bitset.ReadOnlyBitSet
}
// NewConcurrentReadOnlyBloomFilter returns a new concurrent read only bloom
// filter backed by a byte slice, this means it can be used with a mmap'd
// bytes ref. It can be concurrently read from by any number of readers.
func NewConcurrentReadOnlyBloomFilter(
m, k uint,
data []byte,
) *ConcurrentReadOnlyBloomFilter {
return &ConcurrentReadOnlyBloomFilter{
m: uint64(m),
k: uint64(k),
set: bitset.NewReadOnlyBitSet(data),
}
}
// Test if value is in the set.
func (b *ConcurrentReadOnlyBloomFilter) Test(value []byte) bool {
h := sum128WithEntropy(value)
for i := uint64(0); i < b.k; i++ {
if !b.set.Test(bloomFilterLocation(h, i, b.m)) {
return false
}
}
return true
}
// M
3A73
returns the m elements represented.
func (b *ConcurrentReadOnlyBloomFilter) M() uint {
return uint(b.m)
}
// K returns the k hashes used.
func (b *ConcurrentReadOnlyBloomFilter) K() uint {
return uint(b.k)
}
// BitSet returns the bitset used.
func (b *ConcurrentReadOnlyBloomFilter) BitSet() *bitset.ReadOnlyBitSet {
return b.set
}