211 lines
6.1 KiB
Go
211 lines
6.1 KiB
Go
// The MIT License (MIT)
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// Copyright (c) 2014 Andreas Briese, eduToolbox@Bri-C GmbH, Sarstedt
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// Permission is hereby granted, free of charge, to any person obtaining a copy of
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// this software and associated documentation files (the "Software"), to deal in
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// the Software without restriction, including without limitation the rights to
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// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
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// the Software, and to permit persons to whom the Software is furnished to do so,
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// subject to the following conditions:
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
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// FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
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// COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
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// IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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// CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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package z
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import (
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"bytes"
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"encoding/json"
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"log"
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"math"
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"unsafe"
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)
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// helper
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var mask = []uint8{1, 2, 4, 8, 16, 32, 64, 128}
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func getSize(ui64 uint64) (size uint64, exponent uint64) {
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if ui64 < uint64(512) {
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ui64 = uint64(512)
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}
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size = uint64(1)
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for size < ui64 {
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size <<= 1
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exponent++
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}
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return size, exponent
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}
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func calcSizeByWrongPositives(numEntries, wrongs float64) (uint64, uint64) {
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size := -1 * numEntries * math.Log(wrongs) / math.Pow(float64(0.69314718056), 2)
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locs := math.Ceil(float64(0.69314718056) * size / numEntries)
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return uint64(size), uint64(locs)
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}
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// NewBloomFilter returns a new bloomfilter.
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func NewBloomFilter(params ...float64) (bloomfilter *Bloom) {
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var entries, locs uint64
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if len(params) == 2 {
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if params[1] < 1 {
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entries, locs = calcSizeByWrongPositives(params[0], params[1])
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} else {
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entries, locs = uint64(params[0]), uint64(params[1])
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}
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} else {
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log.Fatal("usage: New(float64(number_of_entries), float64(number_of_hashlocations))" +
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" i.e. New(float64(1000), float64(3)) or New(float64(number_of_entries)," +
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" float64(number_of_hashlocations)) i.e. New(float64(1000), float64(0.03))")
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}
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size, exponent := getSize(entries)
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bloomfilter = &Bloom{
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sizeExp: exponent,
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size: size - 1,
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setLocs: locs,
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shift: 64 - exponent,
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}
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bloomfilter.Size(size)
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return bloomfilter
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}
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// Bloom filter
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type Bloom struct {
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bitset []uint64
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ElemNum uint64
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sizeExp uint64
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size uint64
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setLocs uint64
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shift uint64
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}
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// <--- http://www.cse.yorku.ca/~oz/hash.html
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// modified Berkeley DB Hash (32bit)
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// hash is casted to l, h = 16bit fragments
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// func (bl Bloom) absdbm(b *[]byte) (l, h uint64) {
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// hash := uint64(len(*b))
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// for _, c := range *b {
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// hash = uint64(c) + (hash << 6) + (hash << bl.sizeExp) - hash
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// }
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// h = hash >> bl.shift
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// l = hash << bl.shift >> bl.shift
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// return l, h
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// }
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// Add adds hash of a key to the bloomfilter.
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func (bl *Bloom) Add(hash uint64) {
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h := hash >> bl.shift
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l := hash << bl.shift >> bl.shift
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for i := uint64(0); i < bl.setLocs; i++ {
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bl.Set((h + i*l) & bl.size)
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bl.ElemNum++
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}
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}
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// Has checks if bit(s) for entry hash is/are set,
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// returns true if the hash was added to the Bloom Filter.
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func (bl Bloom) Has(hash uint64) bool {
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h := hash >> bl.shift
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l := hash << bl.shift >> bl.shift
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for i := uint64(0); i < bl.setLocs; i++ {
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if !bl.IsSet((h + i*l) & bl.size) {
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return false
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}
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}
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return true
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}
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// AddIfNotHas only Adds hash, if it's not present in the bloomfilter.
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// Returns true if hash was added.
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// Returns false if hash was already registered in the bloomfilter.
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func (bl *Bloom) AddIfNotHas(hash uint64) bool {
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if bl.Has(hash) {
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return false
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}
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bl.Add(hash)
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return true
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}
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// TotalSize returns the total size of the bloom filter.
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func (bl *Bloom) TotalSize() int {
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// The bl struct has 5 members and each one is 8 byte. The bitset is a
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// uint64 byte slice.
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return len(bl.bitset)*8 + 5*8
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}
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// Size makes Bloom filter with as bitset of size sz.
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func (bl *Bloom) Size(sz uint64) {
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bl.bitset = make([]uint64, sz>>6)
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}
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// Clear resets the Bloom filter.
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func (bl *Bloom) Clear() {
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for i := range bl.bitset {
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bl.bitset[i] = 0
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}
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}
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// Set sets the bit[idx] of bitset.
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func (bl *Bloom) Set(idx uint64) {
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ptr := unsafe.Pointer(uintptr(unsafe.Pointer(&bl.bitset[idx>>6])) + uintptr((idx%64)>>3))
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*(*uint8)(ptr) |= mask[idx%8]
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}
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// IsSet checks if bit[idx] of bitset is set, returns true/false.
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func (bl *Bloom) IsSet(idx uint64) bool {
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ptr := unsafe.Pointer(uintptr(unsafe.Pointer(&bl.bitset[idx>>6])) + uintptr((idx%64)>>3))
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r := ((*(*uint8)(ptr)) >> (idx % 8)) & 1
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return r == 1
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}
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// bloomJSONImExport
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// Im/Export structure used by JSONMarshal / JSONUnmarshal
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type bloomJSONImExport struct {
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FilterSet []byte
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SetLocs uint64
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}
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// NewWithBoolset takes a []byte slice and number of locs per entry,
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// returns the bloomfilter with a bitset populated according to the input []byte.
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func newWithBoolset(bs *[]byte, locs uint64) *Bloom {
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bloomfilter := NewBloomFilter(float64(len(*bs)<<3), float64(locs))
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for i, b := range *bs {
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*(*uint8)(unsafe.Pointer(uintptr(unsafe.Pointer(&bloomfilter.bitset[0])) + uintptr(i))) = b
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}
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return bloomfilter
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}
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// JSONUnmarshal takes JSON-Object (type bloomJSONImExport) as []bytes
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// returns bloom32 / bloom64 object.
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func JSONUnmarshal(dbData []byte) (*Bloom, error) {
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bloomImEx := bloomJSONImExport{}
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if err := json.Unmarshal(dbData, &bloomImEx); err != nil {
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return nil, err
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}
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buf := bytes.NewBuffer(bloomImEx.FilterSet)
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bs := buf.Bytes()
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bf := newWithBoolset(&bs, bloomImEx.SetLocs)
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return bf, nil
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}
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// JSONMarshal returns JSON-object (type bloomJSONImExport) as []byte.
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func (bl Bloom) JSONMarshal() []byte {
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bloomImEx := bloomJSONImExport{}
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bloomImEx.SetLocs = bl.setLocs
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bloomImEx.FilterSet = make([]byte, len(bl.bitset)<<3)
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for i := range bloomImEx.FilterSet {
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bloomImEx.FilterSet[i] = *(*byte)(unsafe.Pointer(uintptr(unsafe.Pointer(&bl.bitset[0])) +
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uintptr(i)))
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}
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data, err := json.Marshal(bloomImEx)
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if err != nil {
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log.Fatal("json.Marshal failed: ", err)
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}
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return data
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}
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