1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
|
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package ring implements operations on circular lists.
package ring
// A Ring is an element of a circular list, or ring.
// Rings do not have a beginning or end; a pointer to any ring element
// serves as reference to the entire ring. Empty rings are represented
// as nil Ring pointers. The zero value for a Ring is a one-element
// ring with a nil Value.
//
type Ring struct {
next, prev *Ring
Value interface{} // for use by client; untouched by this library
}
func (r *Ring) init() *Ring {
r.next = r
r.prev = r
return r
}
// Next returns the next ring element. r must not be empty.
func (r *Ring) Next() *Ring {
if r.next == nil {
return r.init()
}
return r.next
}
// Prev returns the previous ring element. r must not be empty.
func (r *Ring) Prev() *Ring {
if r.next == nil {
return r.init()
}
return r.prev
}
// Move moves n % r.Len() elements backward (n < 0) or forward (n >= 0)
// in the ring and returns that ring element. r must not be empty.
//
func (r *Ring) Move(n int) *Ring {
if r.next == nil {
return r.init()
}
switch {
case n < 0:
for ; n < 0; n++ {
r = r.prev
}
case n > 0:
for ; n > 0; n-- {
r = r.next
}
}
return r
}
// New creates a ring of n elements.
func New(n int) *Ring {
if n <= 0 {
return nil
}
r := new(Ring)
p := r
for i := 1; i < n; i++ {
p.next = &Ring{prev: p}
p = p.next
}
p.next = r
r.prev = p
return r
}
// Link connects ring r with ring s such that r.Next()
// becomes s and returns the original value for r.Next().
// r must not be empty.
//
// If r and s point to the same ring, linking
// them removes the elements between r and s from the ring.
// The removed elements form a subring and the result is a
// reference to that subring (if no elements were removed,
// the result is still the original value for r.Next(),
// and not nil).
//
// If r and s point to different rings, linking
// them creates a single ring with the elements of s inserted
// after r. The result points to the element following the
// last element of s after insertion.
//
func (r *Ring) Link(s *Ring) *Ring {
n := r.Next()
if s != nil {
p := s.Prev()
// Note: Cannot use multiple assignment because
// evaluation order of LHS is not specified.
r.next = s
s.prev = r
n.prev = p
p.next = n
}
return n
}
// Unlink removes n % r.Len() elements from the ring r, starting
// at r.Next(). If n % r.Len() == 0, r remains unchanged.
// The result is the removed subring. r must not be empty.
//
func (r *Ring) Unlink(n int) *Ring {
if n <= 0 {
return nil
}
return r.Link(r.Move(n + 1))
}
// Len computes the number of elements in ring r.
// It executes in time proportional to the number of elements.
//
func (r *Ring) Len() int {
n := 0
if r != nil {
n = 1
for p := r.Next(); p != r; p = p.next {
n++
}
}
return n
}
// Do calls function f on each element of the ring, in forward order.
// The behavior of Do is undefined if f changes *r.
func (r *Ring) Do(f func(interface{})) {
if r != nil {
f(r.Value)
for p := r.Next(); p != r; p = p.next {
f(p.Value)
}
}
}
|
