50 lines
857 B
Go
50 lines
857 B
Go
package krpc
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import (
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"crypto/sha1"
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"math"
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"math/bits"
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"net"
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)
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const (
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m = 256 * 8
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k = 2
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)
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type ScrapeBloomFilter [256]byte
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// Note that if you intend for an IP to be in the IPv4 space, you might want to trim it to 4 bytes
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// with IP.To4.
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func (me *ScrapeBloomFilter) AddIp(ip net.IP) {
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h := sha1.New()
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h.Write(ip)
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var sum [20]byte
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h.Sum(sum[:0])
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me.addK(int(sum[0]) | int(sum[1])<<8)
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me.addK(int(sum[2]) | int(sum[3])<<8)
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}
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func (me *ScrapeBloomFilter) addK(index int) {
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index %= m
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me[index/8] |= 1 << (index % 8)
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}
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func (me ScrapeBloomFilter) countZeroes() (ret int) {
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for _, i := range me {
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ret += 8 - bits.OnesCount8(i)
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}
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return
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}
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func (me *ScrapeBloomFilter) EstimateCount() float64 {
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if me == nil {
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return 0
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}
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c := float64(me.countZeroes())
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if c > m-1 {
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c = m - 1
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}
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return math.Log(c/m) / (k * math.Log(1.-1./m))
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}
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