239 lines
7.2 KiB
Go
239 lines
7.2 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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/* This file is a slightly modified file from the go package sources
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and is released on the following license:
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Copyright (c) 2012 The Go Authors. All rights reserved.
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are
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met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above
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copyright notice, this list of conditions and the following disclaimer
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in the documentation and/or other materials provided with the
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distribution.
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* Neither the name of Google Inc. nor the names of its
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contributors may be used to endorse or promote products derived from
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this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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// Package list implements a doubly linked list.
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//
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// To iterate over a list (where l is a *List):
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// for e := l.Front(); e != nil; e = e.Next() {
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// // do something with e.Value
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// }
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//
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package lrucache
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// Element is an element of a linked list.
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type element struct {
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// Next and previous pointers in the doubly-linked list of elements.
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// To simplify the implementation, internally a list l is implemented
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// as a ring, such that &l.root is both the next element of the last
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// list element (l.Back()) and the previous element of the first list
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// element (l.Front()).
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next, prev *element
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// The list to which this element belongs.
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list *list
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// The value stored with this element.
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Value interface{}
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}
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// Next returns the next list element or nil.
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func (e *element) Next() *element {
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if p := e.next; e.list != nil && p != &e.list.root {
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return p
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}
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return nil
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}
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// Prev returns the previous list element or nil.
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func (e *element) Prev() *element {
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if p := e.prev; e.list != nil && p != &e.list.root {
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return p
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}
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return nil
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}
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// List represents a doubly linked list.
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// The zero value for List is an empty list ready to use.
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type list struct {
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root element // sentinel list element, only &root, root.prev, and root.next are used
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len int // current list length excluding (this) sentinel element
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}
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// Init initializes or clears list l.
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func (l *list) Init() *list {
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l.root.next = &l.root
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l.root.prev = &l.root
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l.len = 0
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return l
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}
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// New returns an initialized list.
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// func New() *list { return new(list).Init() }
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// Len returns the number of elements of list l.
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// The complexity is O(1).
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func (l *list) Len() int { return l.len }
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// Front returns the first element of list l or nil
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func (l *list) Front() *element {
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if l.len == 0 {
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return nil
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}
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return l.root.next
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}
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// Back returns the last element of list l or nil.
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func (l *list) Back() *element {
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if l.len == 0 {
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return nil
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}
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return l.root.prev
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}
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// insert inserts e after at, increments l.len, and returns e.
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func (l *list) insert(e, at *element) *element {
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n := at.next
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at.next = e
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e.prev = at
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e.next = n
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n.prev = e
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e.list = l
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l.len++
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return e
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}
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// insertValue is a convenience wrapper for insert(&Element{Value: v}, at).
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func (l *list) insertValue(v interface{}, at *element) *element {
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return l.insert(&element{Value: v}, at)
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}
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// remove removes e from its list, decrements l.len, and returns e.
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func (l *list) remove(e *element) *element {
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e.prev.next = e.next
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e.next.prev = e.prev
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e.next = nil // avoid memory leaks
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e.prev = nil // avoid memory leaks
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e.list = nil
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l.len--
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return e
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}
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// Remove removes e from l if e is an element of list l.
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// It returns the element value e.Value.
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func (l *list) Remove(e *element) interface{} {
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if e.list == l {
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// if e.list == l, l must have been initialized when e was inserted
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// in l or l == nil (e is a zero Element) and l.remove will crash
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l.remove(e)
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}
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return e.Value
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}
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// PushFront inserts a new element e with value v at the front of list l and returns e.
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func (l *list) PushFront(v interface{}) *element {
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return l.insertValue(v, &l.root)
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}
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// PushBack inserts a new element e with value v at the back of list l and returns e.
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func (l *list) PushBack(v interface{}) *element {
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return l.insertValue(v, l.root.prev)
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}
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// InsertBefore inserts a new element e with value v immediately before mark and returns e.
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// If mark is not an element of l, the list is not modified.
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func (l *list) InsertBefore(v interface{}, mark *element) *element {
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if mark.list != l {
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return nil
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}
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// see comment in List.Remove about initialization of l
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return l.insertValue(v, mark.prev)
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}
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// InsertAfter inserts a new element e with value v immediately after mark and returns e.
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// If mark is not an element of l, the list is not modified.
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func (l *list) InsertAfter(v interface{}, mark *element) *element {
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if mark.list != l {
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return nil
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}
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// see comment in List.Remove about initialization of l
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return l.insertValue(v, mark)
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}
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// MoveToFront moves element e to the front of list l.
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// If e is not an element of l, the list is not modified.
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func (l *list) MoveToFront(e *element) {
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if e.list != l || l.root.next == e {
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return
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}
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// see comment in List.Remove about initialization of l
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l.insert(l.remove(e), &l.root)
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}
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// MoveToBack moves element e to the back of list l.
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// If e is not an element of l, the list is not modified.
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func (l *list) MoveToBack(e *element) {
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if e.list != l || l.root.prev == e {
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return
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}
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// see comment in List.Remove about initialization of l
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l.insert(l.remove(e), l.root.prev)
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}
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// MoveBefore moves element e to its new position before mark.
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// If e is not an element of l, or e == mark, the list is not modified.
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func (l *list) MoveBefore(e, mark *element) {
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if e.list != l || e == mark {
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return
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}
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l.insert(l.remove(e), mark.prev)
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}
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// MoveAfter moves element e to its new position after mark.
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// If e is not an element of l, or e == mark, the list is not modified.
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func (l *list) MoveAfter(e, mark *element) {
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if e.list != l || e == mark {
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return
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}
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l.insert(l.remove(e), mark)
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}
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// PushBackList inserts a copy of an other list at the back of list l.
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// The lists l and other may be the same.
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func (l *list) PushBackList(other *list) {
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for i, e := other.Len(), other.Front(); i > 0; i, e = i-1, e.Next() {
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l.insertValue(e.Value, l.root.prev)
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}
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}
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// PushFrontList inserts a copy of an other list at the front of list l.
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// The lists l and other may be the same.
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func (l *list) PushFrontList(other *list) {
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for i, e := other.Len(), other.Back(); i > 0; i, e = i-1, e.Prev() {
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l.insertValue(e.Value, &l.root)
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}
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}
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