mirror of
https://github.com/golang/go
synced 2024-11-22 17:54:45 -07:00
Ring ADT.
- Provides analogous functionality to a doubly-linked list implementation. - Completely symmetric set of operations. - Operations on the ADT do not lead to results that are outside the domain of the ADT (closed interface). - Alternative to container/list. R=rsc DELTA=489 (489 added, 0 deleted, 0 changed) OCL=32284 CL=32323
This commit is contained in:
Robert Griesemer
parent
e50d3ba7e4
commit
6d3d25de21
61
src/pkg/container/ring/Makefile
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61
src/pkg/container/ring/Makefile
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@ -0,0 +1,61 @@
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# 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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# DO NOT EDIT. Automatically generated by gobuild.
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# gobuild -m >Makefile
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D=/container/
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include $(GOROOT)/src/Make.$(GOARCH)
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AR=gopack
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default: packages
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clean:
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rm -rf *.[$(OS)] *.a [$(OS)].out _obj
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test: packages
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gotest
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coverage: packages
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gotest
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6cov -g $$(pwd) | grep -v '_test\.go:'
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%.$O: %.go
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$(GC) -I_obj $*.go
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%.$O: %.c
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$(CC) $*.c
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%.$O: %.s
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$(AS) $*.s
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O1=\
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ring.$O\
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phases: a1
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_obj$D/ring.a: phases
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a1: $(O1)
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$(AR) grc _obj$D/ring.a ring.$O
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rm -f $(O1)
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newpkg: clean
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mkdir -p _obj$D
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$(AR) grc _obj$D/ring.a
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$(O1): newpkg
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$(O2): a1
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nuke: clean
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rm -f $(GOROOT)/pkg/$(GOOS)_$(GOARCH)$D/ring.a
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packages: _obj$D/ring.a
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install: packages
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test -d $(GOROOT)/pkg && mkdir -p $(GOROOT)/pkg/$(GOOS)_$(GOARCH)$D
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cp _obj$D/ring.a $(GOROOT)/pkg/$(GOOS)_$(GOARCH)$D/ring.a
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174
src/pkg/container/ring/ring.go
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174
src/pkg/container/ring/ring.go
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@ -0,0 +1,174 @@
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// 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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// The ring package implements operations on circular lists.
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package ring
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// A Ring is an element of a circular list, or ring.
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// Rings do not have a beginning or end; a pointer to any ring element
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// serves as reference to the entire ring. Empty rings are represented
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// as nil Ring pointers. The zero value for a Ring is a one-element
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// ring with a nil Value.
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//
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type Ring struct {
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next, prev *Ring;
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Value interface{}; // for use by client; untouched by this library
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}
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func (r *Ring) init() *Ring {
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r.next = r;
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r.prev = r;
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return r;
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}
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// Next returns the next ring element. r must not be empty.
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func (r *Ring) Next() *Ring {
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if r.next == nil {
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return r.init();
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}
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return r.next;
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}
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// Prev returns the previous ring element. r must not be empty.
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func (r *Ring) Prev() *Ring {
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if r.next == nil {
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return r.init();
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}
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return r.prev;
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}
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// Move moves n % r.Len() elements backward (n < 0) or forward (n > 0)
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// in the ring and returns that ring element. r must not be empty.
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//
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func (r *Ring) Move(n int) *Ring {
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if r.next == nil {
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return r.init();
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}
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switch {
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case n < 0:
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for ; n < 0; n++ {
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r = r.prev;
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}
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case n > 0:
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for ; n > 0; n-- {
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r = r.next;
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}
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}
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return r;
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}
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// New creates a ring of n elements.
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func New(n int) *Ring {
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if n <= 0 {
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return nil;
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}
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r := new(Ring);
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p := r;
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for i := 1; i < n; i++ {
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p.next = &Ring{prev: p};
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p = p.next;
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}
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p.next = r;
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r.prev = p;
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return r;
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}
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// Link connects ring r with with ring s such that r.Next(1)
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// becomes s and returns the original value for r.Next(1).
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// r must not be empty.
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//
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// If r and s point to the same ring, linking
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// them removes the elements between r and s from the ring.
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// The removed elements form a subring and the result is a
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// reference to that subring (if no elements were removed,
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// the result is still the original value for r.Next(1),
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// and not nil).
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//
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// If r and s point to different rings, linking
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// them creates a single ring with the elements of s inserted
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// after r. The result points to the element following the
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// last element of s after insertion.
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//
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func (r *Ring) Link(s *Ring) *Ring {
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n := r.Next();
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if s != nil {
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p := s.Prev();
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// Note: Cannot use multiple assignment because
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// evaluation order of LHS is not specified.
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r.next = s;
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s.prev = r;
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n.prev = p;
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p.next = n;
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}
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return n;
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}
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// Unlink removes n % r.Len() elements from the ring r, starting
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// at r.Next(). If n % r.Len() == 0, r remains unchanged.
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// The result is the removed subring. r must not be empty.
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//
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func (r *Ring) Unlink(n int) *Ring {
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if n <= 0 {
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return nil;
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}
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return r.Link(r.Move(n + 1));
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}
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// Len computes the number of elements in ring r.
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// It executes in time proportional to the number of elements.
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//
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func (r *Ring) Len() int {
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n := 0;
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if r != nil {
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n = 1;
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for p := r.Next(); p != r; p = p.next {
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n++;
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}
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}
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return n;
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}
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// Forward returns a channel for forward iteration through a ring.
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// Iteration is undefined if the ring is changed during iteration.
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//
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func (r *Ring) Forward() <-chan *Ring {
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c := make(chan *Ring);
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go func() {
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if r != nil {
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c <- r;
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for p := r.Next(); p != r; p = p.next {
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c <- p;
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}
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}
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close(c);
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}();
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return c;
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}
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// Backward returns a channel for backward iteration through a ring.
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// Iteration is undefined if the ring is changed during iteration.
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//
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func (r *Ring) Backward() <-chan *Ring {
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c := make(chan *Ring);
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go func() {
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if r != nil {
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c <- r;
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for p := r.Prev(); p != r; p = p.prev {
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c <- p;
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}
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}
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close(c);
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}();
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return c;
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}
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260
src/pkg/container/ring/ring_test.go
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260
src/pkg/container/ring/ring_test.go
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@ -0,0 +1,260 @@
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// 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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package ring
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import (
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"container/ring";
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"fmt";
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"testing";
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)
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// For debugging - keep around.
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func dump(r *Ring) {
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if r == nil {
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fmt.Println("empty");
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return;
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}
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i, n := 0, r.Len();
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for p := r; i < n; p = p.next {
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fmt.Printf("%4d: %p = {<- %p | %p ->}\n", i, p, p.prev, p.next);
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i++;
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}
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fmt.Println();
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}
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func verify(t *testing.T, r *Ring, N int, sum int) {
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// Len
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n := r.Len();
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if n != N {
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t.Errorf("r.Len() == %d; expected %d", n, N);
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}
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// forward iteration
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n = 0;
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s := 0;
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for p := range r.Forward() {
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n++;
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if p.Value != nil {
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s += p.Value.(int);
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}
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}
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if n != N {
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t.Errorf("number of forward iterations == %d; expected %d", n, N);
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}
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if sum >= 0 && s != sum {
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t.Errorf("forward ring sum = %d; expected %d", s, sum);
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}
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// backward iteration
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n = 0;
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s = 0;
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for p := range r.Backward() {
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n++;
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if p.Value != nil {
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s += p.Value.(int);
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}
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}
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if n != N {
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t.Errorf("number of backward iterations == %d; expected %d", n, N);
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}
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if sum >= 0 && s != sum {
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t.Errorf("backward ring sum = %d; expected %d", s, sum);
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}
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if r == nil {
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return;
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}
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// connections
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if r.next != nil {
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var p *Ring; // previous element
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for q := r; p == nil || q != r; q = q.next {
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if p != nil && p != q.prev {
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t.Errorf("prev = %p, expected q.prev = %p\n", p, q.prev);
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}
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p = q;
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}
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if p != r.prev {
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t.Errorf("prev = %p, expected r.prev = %p\n", p, r.prev);
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}
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}
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// Next, Prev
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if r.Next() != r.next {
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t.Errorf("r.Next() != r.next");
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}
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if r.Prev() != r.prev {
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t.Errorf("r.Prev() != r.prev");
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}
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// Move
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if r.Move(0) != r {
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t.Errorf("r.Move(0) != r");
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}
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if r.Move(N) != r {
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t.Errorf("r.Move(%d) != r", N);
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}
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if r.Move(-N) != r {
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t.Errorf("r.Move(%d) != r", -N);
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}
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for i := 0; i < 10; i++ {
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ni := N + i;
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mi := ni % N;
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if r.Move(ni) != r.Move(mi) {
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t.Errorf("r.Move(%d) != r.Move(%d)", ni, mi);
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}
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if r.Move(-ni) != r.Move(-mi) {
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t.Errorf("r.Move(%d) != r.Move(%d)", -ni, -mi);
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}
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}
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}
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func TestCornerCases(t *testing.T) {
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var (
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r0 *Ring;
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r1 Ring;
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)
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// Basics
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verify(t, r0, 0, 0);
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verify(t, &r1, 1, 0);
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// Insert
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r1.Link(r0);
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verify(t, r0, 0, 0);
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verify(t, &r1, 1, 0);
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// Insert
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r1.Link(r0);
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verify(t, r0, 0, 0);
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verify(t, &r1, 1, 0);
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// Unlink
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r1.Unlink(0);
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verify(t, &r1, 1, 0);
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}
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func makeN(n int) *Ring {
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r := New(n);
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for i := 1; i <= n; i++ {
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r.Value = i;
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r = r.Next();
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}
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return r;
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}
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func sum(r *Ring) int {
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s := 0;
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for p := range r.Forward() {
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s += p.Value.(int);
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}
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return s;
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}
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func sumN(n int) int {
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return (n*n + n)/2;
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}
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func TestNew(t *testing.T) {
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for i := 0; i < 10; i++ {
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r := New(i);
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verify(t, r, i, -1);
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}
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for i := 0; i < 10; i++ {
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r := makeN(i);
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verify(t, r, i, sumN(i));
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}
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}
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func TestLink1(t *testing.T) {
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r1a := makeN(1);
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var r1b Ring;
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r2a := r1a.Link(&r1b);
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verify(t, r2a, 2, 1);
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if r2a != r1a {
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t.Errorf("a) 2-element link failed");
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}
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r2b := r2a.Link(r2a.Next());
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verify(t, r2b, 2, 1);
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if r2b != r2a.Next() {
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t.Errorf("b) 2-element link failed");
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}
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r1c := r2b.Link(r2b);
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verify(t, r1c, 1, 1);
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verify(t, r2b, 1, 0);
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}
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func TestLink2(t *testing.T) {
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var r0 *Ring;
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r1a := &Ring{Value: 42};
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r1b := &Ring{Value: 77};
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r10 := makeN(10);
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r1a.Link(r0);
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verify(t, r1a, 1, 42);
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r1a.Link(r1b);
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verify(t, r1a, 2, 42 + 77);
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r10.Link(r0);
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verify(t, r10, 10, sumN(10));
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r10.Link(r1a);
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verify(t, r10, 12, sumN(10) + 42 + 77);
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}
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func TestLink3(t *testing.T) {
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var r Ring;
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n := 1;
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for i := 1; i < 100; i++ {
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n += i;
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verify(t, r.Link(New(i)), n, -1);
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}
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}
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func TestUnlink(t *testing.T) {
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r10 := makeN(10);
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s10 := r10.Move(6);
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sum10 := sumN(10);
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sum6 := sumN(6);
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verify(t, r10, 10, sum10);
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verify(t, s10, 10, sum10);
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r0 := r10.Unlink(0);
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verify(t, r0, 0, 0);
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r1 := r10.Unlink(1);
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verify(t, r1, 1, 2);
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verify(t, r10, 9, sum10 - 2);
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r9 := r10.Unlink(9);
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verify(t, r9, 9, sum10 - 2);
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verify(t, r10, 9, sum10 - 2);
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}
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func TestLinkUnlink(t *testing.T) {
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for i := 1; i < 4; i++ {
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ri := New(i);
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for j := 0; j < i; j++ {
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rj := ri.Unlink(j);
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verify(t, rj, j, -1);
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verify(t, ri, i-j, -1);
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ri.Link(rj);
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verify(t, ri, i, -1);
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}
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}
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}
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