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wcfs/vendor/lab.nexedi.com/kirr/go123/xcontainer/list/list.go

-// Copyright (C) 2017-2019  Nexedi SA and Contributors.
-//                          Kirill Smelkov <kirr@nexedi.com>
-//
-// This program is free software: you can Use, Study, Modify and Redistribute
-// it under the terms of the GNU General Public License version 3, or (at your
-// option) any later version, as published by the Free Software Foundation.
-//
-// You can also Link and Combine this program with other software covered by
-// the terms of any of the Free Software licenses or any of the Open Source
-// Initiative approved licenses and Convey the resulting work. Corresponding
-// source of such a combination shall include the source code for all other
-// software used.
-//
-// This program is distributed WITHOUT ANY WARRANTY; without even the implied
-// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
-//
-// See COPYING file for full licensing terms.
-// See https://www.nexedi.com/licensing for rationale and options.
-
-// Package list provides intrusive double-linked lists.
-//
-// Go standard library has container/list package which already provides
-// double-linked lists. However in that implementation list itself is kept
-// separate from data structures representing elements. This package provides
-// alternative approach where elements embed necessary list heads which is
-// sometimes more convenient, for example when one wants to move a list
-// element in O(1) starting from pointer to just its data.
-//
-// TODO doc how to get to container of list head via unsafe.OffsetOf.
-package list
-
-// Head is a list head entry for an element in an intrusive doubly-linked list.
-//
-// Zero HEAD value is NOT valid - always call Init() to initialize a head
-// before using it.
-type Head struct {
-	next, prev *Head
-}
-
-func (h *Head) Next() *Head { return h.next }
-func (h *Head) Prev() *Head { return h.prev }
-
-// Init initializes a head making it point to itself via .next and .prev .
-func (h *Head) Init() {
-	h.next = h
-	h.prev = h
-}
-
-// Delete deletes h from its list.
-func (h *Head) Delete() {
-	h.next.prev = h.prev
-	h.prev.next = h.next
-	h.Init()
-}
-
-// MoveBefore moves a to be before b.
-//
-// XXX ok to move if a was not previously on the list?
-func (a *Head) MoveBefore(b *Head) {
-	a.Delete()
-
-	a.next = b
-	a.prev = b.prev
-	b.prev = a
-	a.prev.next = a
-}