1// Copyright ©2014 The Gonum Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5// Package uid implements unique ID provision for graphs.
6package uid
7
8import "gonum.org/v1/gonum/graph/internal/set"
9
10// Max is the maximum value of int64.
11const Max = int64(^uint64(0) >> 1)
12
13// Set implements available ID storage.
14type Set struct {
15	maxID      int64
16	used, free set.Int64s
17}
18
19// NewSet returns a new Set. The returned value should not be passed except by pointer.
20func NewSet() Set {
21	return Set{maxID: -1, used: make(set.Int64s), free: make(set.Int64s)}
22}
23
24// NewID returns a new unique ID. The ID returned is not considered used
25// until passed in a call to use.
26func (s *Set) NewID() int64 {
27	for id := range s.free {
28		return id
29	}
30	if s.maxID != Max {
31		return s.maxID + 1
32	}
33	for id := int64(0); id <= s.maxID+1; id++ {
34		if !s.used.Has(id) {
35			return id
36		}
37	}
38	panic("unreachable")
39}
40
41// Use adds the id to the used IDs in the Set.
42func (s *Set) Use(id int64) {
43	s.used.Add(id)
44	s.free.Remove(id)
45	if id > s.maxID {
46		s.maxID = id
47	}
48}
49
50// Release frees the id for reuse.
51func (s *Set) Release(id int64) {
52	s.free.Add(id)
53	s.used.Remove(id)
54}
55