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binary.go
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binary.go
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package kademlia
import (
"bytes"
"github.com/perlin-network/noise"
"math/bits"
"sort"
)
// XOR allocates a new byte slice with the computed result of XOR(a, b).
func XOR(a, b []byte) []byte {
if len(a) != len(b) {
return a
}
c := make([]byte, len(a))
for i := 0; i < len(a); i++ {
c[i] = a[i] ^ b[i]
}
return c
}
// PrefixDiff counts the number of equal prefixed bits of a and b.
func PrefixDiff(a, b []byte, n int) int {
buf, total := XOR(a, b), 0
for i, b := range buf {
if 8*i >= n {
break
}
if n > 8*i && n < 8*(i+1) {
shift := 8 - uint(n%8)
b >>= shift
}
total += bits.OnesCount8(b)
}
return total
}
// PrefixLen returns the number of prefixed zero bits of a.
func PrefixLen(a []byte) int {
for i, b := range a {
if b != 0 {
return i*8 + bits.LeadingZeros8(b)
}
}
return len(a) * 8
}
// SortByDistance sorts ids by descending XOR distance with respect to id.
func SortByDistance(id noise.PublicKey, ids []noise.ID) []noise.ID {
sort.Slice(ids, func(i, j int) bool {
return bytes.Compare(XOR(ids[i].ID[:], id[:]), XOR(ids[j].ID[:], id[:])) == -1
})
return ids
}