63 lines
1.9 KiB
Go
63 lines
1.9 KiB
Go
package primitives
|
|
|
|
import (
|
|
"crypto/sha256"
|
|
"sync"
|
|
)
|
|
|
|
// BloomFilter implements a bloom filter
|
|
type BloomFilter struct {
|
|
B []bool
|
|
lock sync.Mutex
|
|
}
|
|
|
|
// Init constructs a bloom filter of size m
|
|
func (bf *BloomFilter) Init(m int16) {
|
|
bf.B = make([]bool, m)
|
|
}
|
|
|
|
// Hash transforms a message to a set of bit flips
|
|
// Supports up to m == 65535
|
|
func (bf *BloomFilter) Hash(msg []byte) []int {
|
|
hash := sha256.Sum256(msg)
|
|
|
|
pos1a := (int(hash[0]) + int(hash[1]) + int(hash[2]) + int(hash[3])) % 0xFF
|
|
pos1b := (int(hash[4]) + int(hash[5]) + int(hash[6]) + int(hash[7])) % 0xFF
|
|
pos1 := ((pos1a << 8) + pos1b) & (0xFFFF % len(bf.B))
|
|
|
|
pos2a := (int(hash[8]) + int(hash[9]) + int(hash[10]) + int(hash[11])) % 0xFF
|
|
pos2b := (int(hash[12]) + int(hash[13]) + int(hash[14]) + int(hash[15])) % 0xFF
|
|
pos2 := ((pos2a << 8) + pos2b) & (0xFFFF % len(bf.B))
|
|
|
|
pos3a := (int(hash[16]) + int(hash[17]) + int(hash[18]) + int(hash[19])) % 0xFF
|
|
pos3b := (int(hash[20]) + int(hash[21]) + int(hash[22]) + int(hash[23])) % 0xFF
|
|
pos3 := ((pos3a << 8) + pos3b) & (0xFFFF % len(bf.B))
|
|
|
|
pos4a := (int(hash[24]) + int(hash[25]) + int(hash[26]) + int(hash[27])) % 0xFF
|
|
pos4b := (int(hash[28]) + int(hash[29]) + int(hash[30]) + int(hash[31])) % 0xFF
|
|
pos4 := ((pos4a << 8) + pos4b) & (0xFFFF % len(bf.B))
|
|
|
|
return []int{pos1, pos2, pos3, pos4}
|
|
}
|
|
|
|
// Insert updates the BloomFilter (suitable for concurrent use)
|
|
func (bf *BloomFilter) Insert(msg []byte) {
|
|
pos := bf.Hash(msg)
|
|
bf.lock.Lock()
|
|
defer bf.lock.Unlock()
|
|
bf.B[pos[0]] = true
|
|
bf.B[pos[1]] = true
|
|
bf.B[pos[2]] = true
|
|
bf.B[pos[3]] = true
|
|
}
|
|
|
|
// Check returns true if the messages might be in the BloomFilter
|
|
// (No false positives, possible false negatives due to the probabilistic nature of the filter)
|
|
func (bf *BloomFilter) Check(msg []byte) bool {
|
|
pos := bf.Hash(msg)
|
|
if bf.B[pos[0]] && bf.B[pos[1]] && bf.B[pos[2]] && bf.B[pos[3]] {
|
|
return true
|
|
}
|
|
return false
|
|
}
|