forked from TrueCloudLab/hrw
138 lines
2.8 KiB
Go
138 lines
2.8 KiB
Go
// Package hrw implements Rendezvous hashing.
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// http://en.wikipedia.org/wiki/Rendezvous_hashing.
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package hrw
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import (
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"errors"
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"hash/fnv"
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"reflect"
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"sort"
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"strconv"
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)
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type (
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swapper func(i, j int)
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Hasher interface{ Hash() uint64 }
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hashed struct {
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length int
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sorted []uint64
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weight []uint64
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}
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)
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const m64 = 18446744073709551615 // modulus (2**64-1)
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func weight(x uint64, y uint64) uint64 {
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acc := x ^ y
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acc ^= acc >> 33
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acc = (acc * 0xff51afd7ed558ccd) % m64
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acc ^= acc >> 33
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acc = (acc * 0xc4ceb9fe1a85ec53) % m64
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acc ^= acc >> 33
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return acc
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}
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func (h hashed) Len() int { return h.length }
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func (h hashed) Less(i, j int) bool { return h.weight[h.sorted[i]] < h.weight[h.sorted[j]] }
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func (h hashed) Swap(i, j int) { h.sorted[i], h.sorted[j] = h.sorted[j], h.sorted[i] }
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func SortByWeight(nodes []uint64, hash uint64) []uint64 {
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var (
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l = len(nodes)
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h = hashed{
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length: l,
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sorted: make([]uint64, 0, l),
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weight: make([]uint64, 0, l),
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}
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)
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for i, node := range nodes {
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h.sorted = append(h.sorted, uint64(i))
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h.weight = append(h.weight, weight(node, hash))
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}
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sort.Sort(h)
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return h.sorted
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}
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func SortSliceByValue(slice interface{}, hash uint64) error {
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t := reflect.TypeOf(slice)
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if t.Kind() != reflect.Slice {
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return errors.New("must be slice")
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}
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var (
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val = reflect.ValueOf(slice)
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swap = reflect.Swapper(slice)
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length = val.Len()
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rule = make([]uint64, 0, length)
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)
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if length == 0 {
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return nil
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}
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switch slice := slice.(type) {
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case []int:
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hasher := fnv.New64()
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for i := 0; i < length; i++ {
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hasher.Reset()
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// error always nil
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_, _ = hasher.Write([]byte(strconv.Itoa(slice[i])))
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rule = append(rule, weight(hash, hasher.Sum64()))
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}
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case []string:
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hasher := fnv.New64()
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for i := 0; i < length; i++ {
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hasher.Reset()
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// error always nil
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_, _ = hasher.Write([]byte(slice[i]))
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rule = append(rule, weight(hash, hasher.Sum64()))
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}
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default:
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if _, ok := val.Index(0).Interface().(Hasher); !ok {
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return errors.New("unknown type")
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}
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for i := 0; i < length; i++ {
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h := val.Index(i).Interface().(Hasher)
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rule = append(rule, weight(hash, h.Hash()))
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}
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}
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rule = SortByWeight(rule, hash)
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sortByRule(swap, uint64(length), rule)
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return nil
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}
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func SortSliceByIndex(slice interface{}, hash uint64) {
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length := uint64(reflect.ValueOf(slice).Len())
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swap := reflect.Swapper(slice)
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rule := make([]uint64, 0, length)
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for i := uint64(0); i < length; i++ {
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rule = append(rule, i)
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}
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rule = SortByWeight(rule, hash)
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sortByRule(swap, length, rule)
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}
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func sortByRule(swap swapper, length uint64, rule []uint64) {
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done := make([]bool, length)
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for i := uint64(0); i < length; i++ {
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if done[i] {
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continue
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}
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done[i] = true
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for j := rule[i]; !done[rule[j]]; j = rule[j] {
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swap(int(i), int(j))
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done[j] = true
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}
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}
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}
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