mirror of
https://github.com/autc04/Retro68.git
synced 2024-09-08 20:55:01 +00:00
142 lines
3.2 KiB
Go
142 lines
3.2 KiB
Go
// 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)
|
|
}
|
|
}
|
|
}
|