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package rendezvous
type Rendezvous struct {
nodes map[string]int
nstr []string
nhash []uint64
hash Hasher
}
type Hasher func(s string) uint64
func New(nodes []string, hash Hasher) *Rendezvous {
r := &Rendezvous{
nodes: make(map[string]int, len(nodes)),
nstr: make([]string, len(nodes)),
nhash: make([]uint64, len(nodes)),
hash: hash,
}
for i, n := range nodes {
r.nodes[n] = i
r.nstr[i] = n
r.nhash[i] = hash(n)
}
return r
}
func (r *Rendezvous) Lookup(k string) string {
// short-circuit if we're empty
if len(r.nodes) == 0 {
return ""
}
khash := r.hash(k)
var midx int
var mhash = xorshiftMult64(khash ^ r.nhash[0])
for i, nhash := range r.nhash[1:] {
if h := xorshiftMult64(khash ^ nhash); h > mhash {
midx = i + 1
mhash = h
}
}
return r.nstr[midx]
}
func (r *Rendezvous) Add(node string) {
r.nodes[node] = len(r.nstr)
r.nstr = append(r.nstr, node)
r.nhash = append(r.nhash, r.hash(node))
}
func (r *Rendezvous) Remove(node string) {
// find index of node to remove
nidx := r.nodes[node]
// remove from the slices
l := len(r.nstr)
r.nstr[nidx] = r.nstr[l]
r.nstr = r.nstr[:l]
r.nhash[nidx] = r.nhash[l]
r.nhash = r.nhash[:l]
// update the map
delete(r.nodes, node)
moved := r.nstr[nidx]
r.nodes[moved] = nidx
}
func xorshiftMult64(x uint64) uint64 {
x ^= x >> 12 // a
x ^= x << 25 // b
x ^= x >> 27 // c
return x * 2685821657736338717
}
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