/
filter.go
96 lines (78 loc) · 1.76 KB
/
filter.go
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// package bloom implements a simple bloom filter.
package bloom
import (
"errors"
"fmt"
"hash"
"hash/adler32"
"hash/crc32"
"hash/fnv"
"math/big"
)
type Filter interface {
Add([]byte)
Find([]byte) bool
Merge(Filter) (Filter, error)
}
func BasicFilter() Filter {
// Non crypto hashes, because speed
return NewFilter(2048, adler32.New(), fnv.New32(), crc32.NewIEEE())
}
func NewFilter(size int, hashes ...hash.Hash) Filter {
return &filter{
filter: make([]byte, size),
hashes: hashes,
}
}
type filter struct {
filter []byte
hashes []hash.Hash
}
func (f *filter) Add(k []byte) {
for _, h := range f.hashes {
i := bytesMod(h.Sum(k), int64(len(f.filter)*8))
f.setBit(i)
}
}
func (f *filter) Find(k []byte) bool {
for _, h := range f.hashes {
i := bytesMod(h.Sum(k), int64(len(f.filter)*8))
if !f.getBit(i) {
return false
}
}
return true
}
func (f *filter) setBit(i int64) {
fmt.Printf("setting bit %d\n", i)
f.filter[i/8] |= (1 << byte(i%8))
}
func (f *filter) getBit(i int64) bool {
fmt.Printf("getting bit %d\n", i)
return f.filter[i/8]&(1<<byte(i%8)) != 0
}
func bytesMod(b []byte, modulo int64) int64 {
i := big.NewInt(0)
i = i.SetBytes(b)
bigmod := big.NewInt(int64(modulo))
result := big.NewInt(0)
result.Mod(i, bigmod)
return result.Int64()
}
func (f *filter) Merge(o Filter) (Filter, error) {
casfil, ok := o.(*filter)
if !ok {
return nil, errors.New("Unsupported filter type")
}
if len(casfil.filter) != len(f.filter) {
return nil, errors.New("filter lengths must match!")
}
nfilt := new(filter)
// this bit is sketchy, need a way of comparing hash functions
nfilt.hashes = f.hashes
nfilt.filter = make([]byte, len(f.filter))
for i, v := range f.filter {
nfilt.filter[i] = v | casfil.filter[i]
}
return nfilt, nil
}