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