--- /dev/null
+// 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.
+
+// The ring package 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 with ring s such that r.Next(1)
+// becomes s and returns the original value for r.Next(1).
+// 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(1),
+// 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;
+}
+
+
+// Forward returns a channel for forward iteration through a ring.
+// Iteration is undefined if the ring is changed during iteration.
+//
+func (r *Ring) Forward() <-chan *Ring {
+ c := make(chan *Ring);
+ go func() {
+ if r != nil {
+ c <- r;
+ for p := r.Next(); p != r; p = p.next {
+ c <- p;
+ }
+ }
+ close(c);
+ }();
+ return c;
+}
+
+
+// Backward returns a channel for backward iteration through a ring.
+// Iteration is undefined if the ring is changed during iteration.
+//
+func (r *Ring) Backward() <-chan *Ring {
+ c := make(chan *Ring);
+ go func() {
+ if r != nil {
+ c <- r;
+ for p := r.Prev(); p != r; p = p.prev {
+ c <- p;
+ }
+ }
+ close(c);
+ }();
+ return c;
+}
--- /dev/null
+// 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
+
+import (
+ "container/ring";
+ "fmt";
+ "testing";
+)
+
+
+// For debugging - keep around.
+func dump(r *Ring) {
+ if r == nil {
+ fmt.Println("empty");
+ return;
+ }
+ i, n := 0, r.Len();
+ for p := r; i < n; p = p.next {
+ fmt.Printf("%4d: %p = {<- %p | %p ->}\n", i, p, p.prev, p.next);
+ i++;
+ }
+ fmt.Println();
+}
+
+
+func verify(t *testing.T, r *Ring, N int, sum int) {
+ // Len
+ n := r.Len();
+ if n != N {
+ t.Errorf("r.Len() == %d; expected %d", n, N);
+ }
+
+ // forward iteration
+ n = 0;
+ s := 0;
+ for p := range r.Forward() {
+ n++;
+ if p.Value != nil {
+ s += p.Value.(int);
+ }
+ }
+ if n != N {
+ t.Errorf("number of forward iterations == %d; expected %d", n, N);
+ }
+ if sum >= 0 && s != sum {
+ t.Errorf("forward ring sum = %d; expected %d", s, sum);
+ }
+
+ // backward iteration
+ n = 0;
+ s = 0;
+ for p := range r.Backward() {
+ n++;
+ if p.Value != nil {
+ s += p.Value.(int);
+ }
+ }
+ if n != N {
+ t.Errorf("number of backward iterations == %d; expected %d", n, N);
+ }
+ if sum >= 0 && s != sum {
+ t.Errorf("backward ring sum = %d; expected %d", s, sum);
+ }
+
+ if r == nil {
+ return;
+ }
+
+ // connections
+ if r.next != nil {
+ var p *Ring; // previous element
+ for q := r; p == nil || q != r; q = q.next {
+ if p != nil && p != q.prev {
+ t.Errorf("prev = %p, expected q.prev = %p\n", p, q.prev);
+ }
+ p = q;
+ }
+ if p != r.prev {
+ t.Errorf("prev = %p, expected r.prev = %p\n", p, r.prev);
+ }
+ }
+
+ // Next, Prev
+ if r.Next() != r.next {
+ t.Errorf("r.Next() != r.next");
+ }
+ if r.Prev() != r.prev {
+ t.Errorf("r.Prev() != r.prev");
+ }
+
+ // Move
+ if r.Move(0) != r {
+ t.Errorf("r.Move(0) != r");
+ }
+ if r.Move(N) != r {
+ t.Errorf("r.Move(%d) != r", N);
+ }
+ if r.Move(-N) != r {
+ t.Errorf("r.Move(%d) != r", -N);
+ }
+ for i := 0; i < 10; i++ {
+ ni := N + i;
+ mi := ni % N;
+ if r.Move(ni) != r.Move(mi) {
+ t.Errorf("r.Move(%d) != r.Move(%d)", ni, mi);
+ }
+ if r.Move(-ni) != r.Move(-mi) {
+ t.Errorf("r.Move(%d) != r.Move(%d)", -ni, -mi);
+ }
+ }
+}
+
+
+func TestCornerCases(t *testing.T) {
+ var (
+ r0 *Ring;
+ r1 Ring;
+ )
+ // Basics
+ verify(t, r0, 0, 0);
+ verify(t, &r1, 1, 0);
+ // Insert
+ r1.Link(r0);
+ verify(t, r0, 0, 0);
+ verify(t, &r1, 1, 0);
+ // Insert
+ r1.Link(r0);
+ verify(t, r0, 0, 0);
+ verify(t, &r1, 1, 0);
+ // Unlink
+ r1.Unlink(0);
+ verify(t, &r1, 1, 0);
+}
+
+
+func makeN(n int) *Ring {
+ r := New(n);
+ for i := 1; i <= n; i++ {
+ r.Value = i;
+ r = r.Next();
+ }
+ return r;
+}
+
+
+func sum(r *Ring) int {
+ s := 0;
+ for p := range r.Forward() {
+ s += p.Value.(int);
+ }
+ return s;
+}
+
+
+func sumN(n int) int {
+ return (n*n + n)/2;
+}
+
+
+func TestNew(t *testing.T) {
+ for i := 0; i < 10; i++ {
+ r := New(i);
+ verify(t, r, i, -1);
+ }
+ for i := 0; i < 10; i++ {
+ r := makeN(i);
+ verify(t, r, i, sumN(i));
+ }
+}
+
+
+func TestLink1(t *testing.T) {
+ r1a := makeN(1);
+ var r1b Ring;
+ r2a := r1a.Link(&r1b);
+ verify(t, r2a, 2, 1);
+ if r2a != r1a {
+ t.Errorf("a) 2-element link failed");
+ }
+
+ r2b := r2a.Link(r2a.Next());
+ verify(t, r2b, 2, 1);
+ if r2b != r2a.Next() {
+ t.Errorf("b) 2-element link failed");
+ }
+
+ r1c := r2b.Link(r2b);
+ verify(t, r1c, 1, 1);
+ verify(t, r2b, 1, 0);
+}
+
+
+func TestLink2(t *testing.T) {
+ var r0 *Ring;
+ r1a := &Ring{Value: 42};
+ r1b := &Ring{Value: 77};
+ r10 := makeN(10);
+
+ r1a.Link(r0);
+ verify(t, r1a, 1, 42);
+
+ r1a.Link(r1b);
+ verify(t, r1a, 2, 42 + 77);
+
+ r10.Link(r0);
+ verify(t, r10, 10, sumN(10));
+
+ r10.Link(r1a);
+ verify(t, r10, 12, sumN(10) + 42 + 77);
+}
+
+
+func TestLink3(t *testing.T) {
+ var r Ring;
+ n := 1;
+ for i := 1; i < 100; i++ {
+ n += i;
+ verify(t, r.Link(New(i)), n, -1);
+ }
+}
+
+
+func TestUnlink(t *testing.T) {
+ r10 := makeN(10);
+ s10 := r10.Move(6);
+
+ sum10 := sumN(10);
+ sum6 := sumN(6);
+
+ verify(t, r10, 10, sum10);
+ verify(t, s10, 10, sum10);
+
+ r0 := r10.Unlink(0);
+ verify(t, r0, 0, 0);
+
+ r1 := r10.Unlink(1);
+ verify(t, r1, 1, 2);
+ verify(t, r10, 9, sum10 - 2);
+
+ r9 := r10.Unlink(9);
+ verify(t, r9, 9, sum10 - 2);
+ verify(t, r10, 9, sum10 - 2);
+}
+
+
+func TestLinkUnlink(t *testing.T) {
+ for i := 1; i < 4; i++ {
+ ri := New(i);
+ for j := 0; j < i; j++ {
+ rj := ri.Unlink(j);
+ verify(t, rj, j, -1);
+ verify(t, ri, i-j, -1);
+ ri.Link(rj);
+ verify(t, ri, i, -1);
+ }
+ }
+}