container/intsets/sparse_test.go - tools - Git at Google

 // Copyright 2014 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 intsets_test

 import (
 	"fmt"
 	"log"
 	"math/rand"
 	"sort"
 	"strings"
 	"testing"

 	"golang.org/x/tools/container/intsets"
 )

 func TestBasics(t *testing.T) {
 	var s intsets.Sparse
 	if len := s.Len(); len != 0 {
 		t.Errorf("Len({}): got %d, want 0", len)
 	}
 	if s := s.String(); s != "{}" {
 		t.Errorf("String({}): got %q, want \"{}\"", s)
 	}
 	if s.Has(3) {
 		t.Errorf("Has(3): got true, want false")
 	}
 	if err := s.Check(); err != nil {
 		t.Error(err)
 	}

 	if !s.Insert(3) {
 		t.Errorf("Insert(3): got false, want true")
 	}
 	if max := s.Max(); max != 3 {
 		t.Errorf("Max: got %d, want 3", max)
 	}

 	if !s.Insert(435) {
 		t.Errorf("Insert(435): got false, want true")
 	}
 	if s := s.String(); s != "{3 435}" {
 		t.Errorf("String({3 435}): got %q, want \"{3 435}\"", s)
 	}
 	if max := s.Max(); max != 435 {
 		t.Errorf("Max: got %d, want 435", max)
 	}
 	if len := s.Len(); len != 2 {
 		t.Errorf("Len: got %d, want 2", len)
 	}

 	if !s.Remove(435) {
 		t.Errorf("Remove(435): got false, want true")
 	}
 	if s := s.String(); s != "{3}" {
 		t.Errorf("String({3}): got %q, want \"{3}\"", s)
 	}
 }

 // Insert, Len, IsEmpty, Hash, Clear, AppendTo.
 func TestMoreBasics(t *testing.T) {
 	set := new(intsets.Sparse)
 	set.Insert(456)
 	set.Insert(123)
 	set.Insert(789)
 	if set.Len() != 3 {
 		t.Errorf("%s.Len: got %d, want 3", set, set.Len())
 	}
 	if set.IsEmpty() {
 		t.Errorf("%s.IsEmpty: got true", set)
 	}
 	if !set.Has(123) {
 		t.Errorf("%s.Has(123): got false", set)
 	}
 	if set.Has(1234) {
 		t.Errorf("%s.Has(1234): got true", set)
 	}
 	got := set.AppendTo([]int{-1})
 	if want := []int{-1, 123, 456, 789}; fmt.Sprint(got) != fmt.Sprint(want) {
 		t.Errorf("%s.AppendTo: got %v, want %v", set, got, want)
 	}

 	set.Clear()

 	if set.Len() != 0 {
 		t.Errorf("Clear: got %d, want 0", set.Len())
 	}
 	if !set.IsEmpty() {
 		t.Errorf("IsEmpty: got false")
 	}
 	if set.Has(123) {
 		t.Errorf("%s.Has: got false", set)
 	}
 }

 func TestTakeMin(t *testing.T) {
 	var set intsets.Sparse
 	set.Insert(456)
 	set.Insert(123)
 	set.Insert(789)
 	set.Insert(-123)
 	var got int
 	for i, want := range []int{-123, 123, 456, 789} {
 		if !set.TakeMin(&got) || got != want {
 			t.Errorf("TakeMin #%d: got %d, want %d", i, got, want)
 		}
 	}
 	if set.TakeMin(&got) {
 		t.Errorf("%s.TakeMin returned true", &set)
 	}
 	if err := set.Check(); err != nil {
 		t.Fatalf("check: %s: %#v", err, &set)
 	}
 }

 func TestMinAndMax(t *testing.T) {
 	values := []int{0, 456, 123, 789, -123} // elt 0 => empty set
 	wantMax := []int{intsets.MinInt, 456, 456, 789, 789}
 	wantMin := []int{intsets.MaxInt, 456, 123, 123, -123}

 	var set intsets.Sparse
 	for i, x := range values {
 		if i != 0 {
 			set.Insert(x)
 		}
 		if got, want := set.Min(), wantMin[i]; got != want {
 			t.Errorf("Min #%d: got %d, want %d", i, got, want)
 		}
 		if got, want := set.Max(), wantMax[i]; got != want {
 			t.Errorf("Max #%d: got %d, want %d", i, got, want)
 		}
 	}

 	set.Insert(intsets.MinInt)
 	if got, want := set.Min(), intsets.MinInt; got != want {
 		t.Errorf("Min: got %d, want %d", got, want)
 	}

 	set.Insert(intsets.MaxInt)
 	if got, want := set.Max(), intsets.MaxInt; got != want {
 		t.Errorf("Max: got %d, want %d", got, want)
 	}
 }

 func TestEquals(t *testing.T) {
 	var setX intsets.Sparse
 	setX.Insert(456)
 	setX.Insert(123)
 	setX.Insert(789)

 	if !setX.Equals(&setX) {
 		t.Errorf("Equals(%s, %s): got false", &setX, &setX)
 	}

 	var setY intsets.Sparse
 	setY.Insert(789)
 	setY.Insert(456)
 	setY.Insert(123)

 	if !setX.Equals(&setY) {
 		t.Errorf("Equals(%s, %s): got false", &setX, &setY)
 	}

 	setY.Insert(1)
 	if setX.Equals(&setY) {
 		t.Errorf("Equals(%s, %s): got true", &setX, &setY)
 	}

 	var empty intsets.Sparse
 	if setX.Equals(&empty) {
 		t.Errorf("Equals(%s, %s): got true", &setX, &empty)
 	}

 	// Edge case: some block (with offset=0) appears in X but not Y.
 	setY.Remove(123)
 	if setX.Equals(&setY) {
 		t.Errorf("Equals(%s, %s): got true", &setX, &setY)
 	}
 }

 // A pset is a parallel implementation of a set using both an intsets.Sparse
 // and a built-in hash map.
 type pset struct {
 	hash map[int]bool
 	bits intsets.Sparse
 }

 func makePset() *pset {
 	return &pset{hash: make(map[int]bool)}
 }

 func (set *pset) add(n int) {
 	prev := len(set.hash)
 	set.hash[n] = true
 	grewA := len(set.hash) > prev

 	grewB := set.bits.Insert(n)

 	if grewA != grewB {
 		panic(fmt.Sprintf("add(%d): grewA=%t grewB=%t", n, grewA, grewB))
 	}
 }

 func (set *pset) remove(n int) {
 	prev := len(set.hash)
 	delete(set.hash, n)
 	shrankA := len(set.hash) < prev

 	shrankB := set.bits.Remove(n)

 	if shrankA != shrankB {
 		panic(fmt.Sprintf("remove(%d): shrankA=%t shrankB=%t", n, shrankA, shrankB))
 	}
 }

 func (set *pset) check(t *testing.T, msg string) {
 	var eltsA []int
 	for elt := range set.hash {
 		eltsA = append(eltsA, int(elt))
 	}
 	sort.Ints(eltsA)

 	eltsB := set.bits.AppendTo(nil)

 	if a, b := fmt.Sprint(eltsA), fmt.Sprint(eltsB); a != b {
 		t.Errorf("check(%s): hash=%s bits=%s (%s)", msg, a, b, &set.bits)
 	}

 	if err := set.bits.Check(); err != nil {
 		t.Fatalf("Check(%s): %s: %#v", msg, err, &set.bits)
 	}
 }

 // randomPset returns a parallel set of random size and elements.
 func randomPset(prng *rand.Rand, maxSize int) *pset {
 	set := makePset()
 	size := int(prng.Int()) % maxSize
 	for i := 0; i < size; i++ {
 		// TODO(adonovan): benchmark how performance varies
 		// with this sparsity parameter.
 		n := int(prng.Int()) % 10000
 		set.add(n)
 	}
 	return set
 }

 // TestRandomMutations performs the same random adds/removes on two
 // set implementations and ensures that they compute the same result.
 func TestRandomMutations(t *testing.T) {
 	const debug = false

 	set := makePset()
 	prng := rand.New(rand.NewSource(0))
 	for i := 0; i < 10000; i++ {
 		n := int(prng.Int())%2000 - 1000
 		if i%2 == 0 {
 			if debug {
 				log.Printf("add %d", n)
 			}
 			set.add(n)
 		} else {
 			if debug {
 				log.Printf("remove %d", n)
 			}
 			set.remove(n)
 		}
 		if debug {
 			set.check(t, "post mutation")
 		}
 	}
 	set.check(t, "final")
 	if debug {
 		log.Print(&set.bits)
 	}
 }

 func TestLowerBound(t *testing.T) {
 	// Use random sets of sizes from 0 to about 4000.
 	prng := rand.New(rand.NewSource(0))
 	for i := uint(0); i < 12; i++ {
 		x := randomPset(prng, 1<<i)
 		for j := 0; j < 10000; j++ {
 			found := intsets.MaxInt
 			for e := range x.hash {
 				if e >= j && e < found {
 					found = e
 				}
 			}
 			if res := x.bits.LowerBound(j); res != found {
 				t.Errorf("%s: LowerBound(%d)=%d, expected %d", &x.bits, j, res, found)
 			}
 		}
 	}
 }

 // TestSetOperations exercises classic set operations: ∩ , ∪, \.
 func TestSetOperations(t *testing.T) {
 	prng := rand.New(rand.NewSource(0))

 	// Use random sets of sizes from 0 to about 4000.
 	// For each operator, we test variations such as
 	// Z.op(X, Y), Z.op(X, Z) and Z.op(Z, Y) to exercise
 	// the degenerate cases of each method implementation.
 	for i := uint(0); i < 12; i++ {
 		X := randomPset(prng, 1<<i)
 		Y := randomPset(prng, 1<<i)

 		// TODO(adonovan): minimise dependencies between stanzas below.

 		// Copy(X)
 		C := makePset()
 		C.bits.Copy(&Y.bits) // no effect on result
 		C.bits.Copy(&X.bits)
 		C.hash = X.hash
 		C.check(t, "C.Copy(X)")
 		C.bits.Copy(&C.bits)
 		C.check(t, "C.Copy(C)")

 		// U.Union(X, Y)
 		U := makePset()
 		U.bits.Union(&X.bits, &Y.bits)
 		for n := range X.hash {
 			U.hash[n] = true
 		}
 		for n := range Y.hash {
 			U.hash[n] = true
 		}
 		U.check(t, "U.Union(X, Y)")

 		// U.Union(X, X)
 		U.bits.Union(&X.bits, &X.bits)
 		U.hash = X.hash
 		U.check(t, "U.Union(X, X)")

 		// U.Union(U, Y)
 		U = makePset()
 		U.bits.Copy(&X.bits)
 		U.bits.Union(&U.bits, &Y.bits)
 		for n := range X.hash {
 			U.hash[n] = true
 		}
 		for n := range Y.hash {
 			U.hash[n] = true
 		}
 		U.check(t, "U.Union(U, Y)")

 		// U.Union(X, U)
 		U.bits.Copy(&Y.bits)
 		U.bits.Union(&X.bits, &U.bits)
 		U.check(t, "U.Union(X, U)")

 		// U.UnionWith(U)
 		U.bits.UnionWith(&U.bits)
 		U.check(t, "U.UnionWith(U)")

 		// I.Intersection(X, Y)
 		I := makePset()
 		I.bits.Intersection(&X.bits, &Y.bits)
 		for n := range X.hash {
 			if Y.hash[n] {
 				I.hash[n] = true
 			}
 		}
 		I.check(t, "I.Intersection(X, Y)")

 		// I.Intersection(X, X)
 		I.bits.Intersection(&X.bits, &X.bits)
 		I.hash = X.hash
 		I.check(t, "I.Intersection(X, X)")

 		// I.Intersection(I, X)
 		I.bits.Intersection(&I.bits, &X.bits)
 		I.check(t, "I.Intersection(I, X)")

 		// I.Intersection(X, I)
 		I.bits.Intersection(&X.bits, &I.bits)
 		I.check(t, "I.Intersection(X, I)")

 		// I.Intersection(I, I)
 		I.bits.Intersection(&I.bits, &I.bits)
 		I.check(t, "I.Intersection(I, I)")

 		// D.Difference(X, Y)
 		D := makePset()
 		D.bits.Difference(&X.bits, &Y.bits)
 		for n := range X.hash {
 			if !Y.hash[n] {
 				D.hash[n] = true
 			}
 		}
 		D.check(t, "D.Difference(X, Y)")

 		// D.Difference(D, Y)
 		D.bits.Copy(&X.bits)
 		D.bits.Difference(&D.bits, &Y.bits)
 		D.check(t, "D.Difference(D, Y)")

 		// D.Difference(Y, D)
 		D.bits.Copy(&X.bits)
 		D.bits.Difference(&Y.bits, &D.bits)
 		D.hash = make(map[int]bool)
 		for n := range Y.hash {
 			if !X.hash[n] {
 				D.hash[n] = true
 			}
 		}
 		D.check(t, "D.Difference(Y, D)")

 		// D.Difference(X, X)
 		D.bits.Difference(&X.bits, &X.bits)
 		D.hash = nil
 		D.check(t, "D.Difference(X, X)")

 		// D.DifferenceWith(D)
 		D.bits.Copy(&X.bits)
 		D.bits.DifferenceWith(&D.bits)
 		D.check(t, "D.DifferenceWith(D)")

 		// SD.SymmetricDifference(X, Y)
 		SD := makePset()
 		SD.bits.SymmetricDifference(&X.bits, &Y.bits)
 		for n := range X.hash {
 			if !Y.hash[n] {
 				SD.hash[n] = true
 			}
 		}
 		for n := range Y.hash {
 			if !X.hash[n] {
 				SD.hash[n] = true
 			}
 		}
 		SD.check(t, "SD.SymmetricDifference(X, Y)")

 		// X.SymmetricDifferenceWith(Y)
 		SD.bits.Copy(&X.bits)
 		SD.bits.SymmetricDifferenceWith(&Y.bits)
 		SD.check(t, "X.SymmetricDifference(Y)")

 		// Y.SymmetricDifferenceWith(X)
 		SD.bits.Copy(&Y.bits)
 		SD.bits.SymmetricDifferenceWith(&X.bits)
 		SD.check(t, "Y.SymmetricDifference(X)")

 		// SD.SymmetricDifference(X, X)
 		SD.bits.SymmetricDifference(&X.bits, &X.bits)
 		SD.hash = nil
 		SD.check(t, "SD.SymmetricDifference(X, X)")

 		// SD.SymmetricDifference(X, Copy(X))
 		X2 := makePset()
 		X2.bits.Copy(&X.bits)
 		SD.bits.SymmetricDifference(&X.bits, &X2.bits)
 		SD.check(t, "SD.SymmetricDifference(X, Copy(X))")

 		// Copy(X).SymmetricDifferenceWith(X)
 		SD.bits.Copy(&X.bits)
 		SD.bits.SymmetricDifferenceWith(&X.bits)
 		SD.check(t, "Copy(X).SymmetricDifferenceWith(X)")
 	}
 }

 func TestIntersectionWith(t *testing.T) {
 	// Edge cases: the pairs (1,1), (1000,2000), (8000,4000)
 	// exercise the <, >, == cases in IntersectionWith that the
 	// TestSetOperations data is too dense to cover.
 	var X, Y intsets.Sparse
 	X.Insert(1)
 	X.Insert(1000)
 	X.Insert(8000)
 	Y.Insert(1)
 	Y.Insert(2000)
 	Y.Insert(4000)
 	X.IntersectionWith(&Y)
 	if got, want := X.String(), "{1}"; got != want {
 		t.Errorf("IntersectionWith: got %s, want %s", got, want)
 	}
 }

 func TestIntersects(t *testing.T) {
 	prng := rand.New(rand.NewSource(0))

 	for i := uint(0); i < 12; i++ {
 		X, Y := randomPset(prng, 1<<i), randomPset(prng, 1<<i)
 		x, y := &X.bits, &Y.bits

 		// test the slow way
 		var z intsets.Sparse
 		z.Copy(x)
 		z.IntersectionWith(y)

 		if got, want := x.Intersects(y), !z.IsEmpty(); got != want {
 			t.Errorf("Intersects(%s, %s): got %v, want %v (%s)", x, y, got, want, &z)
 		}

 		// make it false
 		a := x.AppendTo(nil)
 		for _, v := range a {
 			y.Remove(v)
 		}

 		if got, want := x.Intersects(y), false; got != want {
 			t.Errorf("Intersects: got %v, want %v", got, want)
 		}

 		// make it true
 		if x.IsEmpty() {
 			continue
 		}
 		i := prng.Intn(len(a))
 		y.Insert(a[i])

 		if got, want := x.Intersects(y), true; got != want {
 			t.Errorf("Intersects: got %v, want %v", got, want)
 		}
 	}
 }

 func TestSubsetOf(t *testing.T) {
 	prng := rand.New(rand.NewSource(0))

 	for i := uint(0); i < 12; i++ {
 		X, Y := randomPset(prng, 1<<i), randomPset(prng, 1<<i)
 		x, y := &X.bits, &Y.bits

 		// test the slow way
 		var z intsets.Sparse
 		z.Copy(x)
 		z.DifferenceWith(y)

 		if got, want := x.SubsetOf(y), z.IsEmpty(); got != want {
 			t.Errorf("SubsetOf: got %v, want %v", got, want)
 		}

 		// make it true
 		y.UnionWith(x)

 		if got, want := x.SubsetOf(y), true; got != want {
 			t.Errorf("SubsetOf: got %v, want %v", got, want)
 		}

 		// make it false
 		if x.IsEmpty() {
 			continue
 		}
 		a := x.AppendTo(nil)
 		i := prng.Intn(len(a))
 		y.Remove(a[i])

 		if got, want := x.SubsetOf(y), false; got != want {
 			t.Errorf("SubsetOf: got %v, want %v", got, want)
 		}
 	}
 }

 func TestBitString(t *testing.T) {
 	for _, test := range []struct {
 		input []int
 		want  string
 	}{
 		{nil, "0"},
 		{[]int{0}, "1"},
 		{[]int{0, 4, 5}, "110001"},
 		{[]int{0, 7, 177}, "1" + strings.Repeat("0", 169) + "10000001"},
 		{[]int{-3, 0, 4, 5}, "110001.001"},
 		{[]int{-3}, "0.001"},
 	} {
 		var set intsets.Sparse
 		for _, x := range test.input {
 			set.Insert(x)
 		}
 		if got := set.BitString(); got != test.want {
 			t.Errorf("BitString(%s) = %s, want %s", set.String(), got, test.want)
 		}
 	}
 }

 func TestFailFastOnShallowCopy(t *testing.T) {
 	var x intsets.Sparse
 	x.Insert(1)

 	y := x // shallow copy (breaks representation invariants)
 	defer func() {
 		got := fmt.Sprint(recover())
 		want := "interface conversion: interface {} is nil, not intsets.to_copy_a_sparse_you_must_call_its_Copy_method"
 		if got != want {
 			t.Errorf("shallow copy: recover() = %q, want %q", got, want)
 		}
 	}()
 	y.String() // panics
 	t.Error("didn't panic as expected")
 }

 // -- Benchmarks -------------------------------------------------------

 // TODO(adonovan):
 // - Add benchmarks of each method.
 // - Gather set distributions from pointer analysis.
 // - Measure memory usage.

 func benchmarkInsertProbeSparse(b *testing.B, size, spread int) {
 	prng := rand.New(rand.NewSource(0))
 	// Generate our insertions and probes beforehand (we don't want to benchmark
 	// the prng).
 	insert := make([]int, size)
 	probe := make([]int, size*2)
 	for i := range insert {
 		insert[i] = prng.Int() % spread
 	}
 	for i := range probe {
 		probe[i] = prng.Int() % spread
 	}

 	b.ResetTimer()
 	var x intsets.Sparse
 	for tries := 0; tries < b.N; tries++ {
 		x.Clear()
 		for _, n := range insert {
 			x.Insert(n)
 		}
 		hits := 0
 		for _, n := range probe {
 			if x.Has(n) {
 				hits++
 			}
 		}
 		// Use the variable so it doesn't get optimized away.
 		if hits > len(probe) {
 			b.Fatalf("%d hits, only %d probes", hits, len(probe))
 		}
 	}
 }

 func BenchmarkInsertProbeSparse_2_10(b *testing.B) {
 	benchmarkInsertProbeSparse(b, 2, 10)
 }

 func BenchmarkInsertProbeSparse_10_10(b *testing.B) {
 	benchmarkInsertProbeSparse(b, 10, 10)
 }

 func BenchmarkInsertProbeSparse_10_1000(b *testing.B) {
 	benchmarkInsertProbeSparse(b, 10, 1000)
 }

 func BenchmarkInsertProbeSparse_100_100(b *testing.B) {
 	benchmarkInsertProbeSparse(b, 100, 100)
 }

 func BenchmarkInsertProbeSparse_100_10000(b *testing.B) {
 	benchmarkInsertProbeSparse(b, 100, 1000)
 }

 func BenchmarkUnionDifferenceSparse(b *testing.B) {
 	prng := rand.New(rand.NewSource(0))
 	for tries := 0; tries < b.N; tries++ {
 		var x, y, z intsets.Sparse
 		for i := 0; i < 1000; i++ {
 			n := int(prng.Int()) % 100000
 			if i%2 == 0 {
 				x.Insert(n)
 			} else {
 				y.Insert(n)
 			}
 		}
 		z.Union(&x, &y)
 		z.Difference(&x, &y)
 	}
 }

 func BenchmarkUnionDifferenceHashTable(b *testing.B) {
 	prng := rand.New(rand.NewSource(0))
 	for tries := 0; tries < b.N; tries++ {
 		x, y, z := make(map[int]bool), make(map[int]bool), make(map[int]bool)
 		for i := 0; i < 1000; i++ {
 			n := int(prng.Int()) % 100000
 			if i%2 == 0 {
 				x[n] = true
 			} else {
 				y[n] = true
 			}
 		}
 		// union
 		for n := range x {
 			z[n] = true
 		}
 		for n := range y {
 			z[n] = true
 		}
 		// difference
 		z = make(map[int]bool)
 		for n := range y {
 			if !x[n] {
 				z[n] = true
 			}
 		}
 	}
 }

 func BenchmarkAppendTo(b *testing.B) {
 	prng := rand.New(rand.NewSource(0))
 	var x intsets.Sparse
 	for i := 0; i < 1000; i++ {
 		x.Insert(int(prng.Int()) % 10000)
 	}
 	var space [1000]int
 	for tries := 0; tries < b.N; tries++ {
 		x.AppendTo(space[:0])
 	}
 }
	// Copyright 2014 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 intsets_test

	import (
	"fmt"
	"log"
	"math/rand"
	"sort"
	"strings"
	"testing"

	"golang.org/x/tools/container/intsets"
	)

	func TestBasics(t *testing.T) {
	var s intsets.Sparse
	if len := s.Len(); len != 0 {
	t.Errorf("Len({}): got %d, want 0", len)
	}
	if s := s.String(); s != "{}" {
	t.Errorf("String({}): got %q, want \"{}\"", s)
	}
	if s.Has(3) {
	t.Errorf("Has(3): got true, want false")
	}
	if err := s.Check(); err != nil {
	t.Error(err)
	}

	if !s.Insert(3) {
	t.Errorf("Insert(3): got false, want true")
	}
	if max := s.Max(); max != 3 {
	t.Errorf("Max: got %d, want 3", max)
	}

	if !s.Insert(435) {
	t.Errorf("Insert(435): got false, want true")
	}
	if s := s.String(); s != "{3 435}" {
	t.Errorf("String({3 435}): got %q, want \"{3 435}\"", s)
	}
	if max := s.Max(); max != 435 {
	t.Errorf("Max: got %d, want 435", max)
	}
	if len := s.Len(); len != 2 {
	t.Errorf("Len: got %d, want 2", len)
	}

	if !s.Remove(435) {
	t.Errorf("Remove(435): got false, want true")
	}
	if s := s.String(); s != "{3}" {
	t.Errorf("String({3}): got %q, want \"{3}\"", s)
	}
	}

	// Insert, Len, IsEmpty, Hash, Clear, AppendTo.
	func TestMoreBasics(t *testing.T) {
	set := new(intsets.Sparse)
	set.Insert(456)
	set.Insert(123)
	set.Insert(789)
	if set.Len() != 3 {
	t.Errorf("%s.Len: got %d, want 3", set, set.Len())
	}
	if set.IsEmpty() {
	t.Errorf("%s.IsEmpty: got true", set)
	}
	if !set.Has(123) {
	t.Errorf("%s.Has(123): got false", set)
	}
	if set.Has(1234) {
	t.Errorf("%s.Has(1234): got true", set)
	}
	got := set.AppendTo([]int{-1})
	if want := []int{-1, 123, 456, 789}; fmt.Sprint(got) != fmt.Sprint(want) {
	t.Errorf("%s.AppendTo: got %v, want %v", set, got, want)
	}

	set.Clear()

	if set.Len() != 0 {
	t.Errorf("Clear: got %d, want 0", set.Len())
	}
	if !set.IsEmpty() {
	t.Errorf("IsEmpty: got false")
	}
	if set.Has(123) {
	t.Errorf("%s.Has: got false", set)
	}
	}

	func TestTakeMin(t *testing.T) {
	var set intsets.Sparse
	set.Insert(456)
	set.Insert(123)
	set.Insert(789)
	set.Insert(-123)
	var got int
	for i, want := range []int{-123, 123, 456, 789} {
	if !set.TakeMin(&got) \|\| got != want {
	t.Errorf("TakeMin #%d: got %d, want %d", i, got, want)
	}
	}
	if set.TakeMin(&got) {
	t.Errorf("%s.TakeMin returned true", &set)
	}
	if err := set.Check(); err != nil {
	t.Fatalf("check: %s: %#v", err, &set)
	}
	}

	func TestMinAndMax(t *testing.T) {
	values := []int{0, 456, 123, 789, -123} // elt 0 => empty set
	wantMax := []int{intsets.MinInt, 456, 456, 789, 789}
	wantMin := []int{intsets.MaxInt, 456, 123, 123, -123}

	var set intsets.Sparse
	for i, x := range values {
	if i != 0 {
	set.Insert(x)
	}
	if got, want := set.Min(), wantMin[i]; got != want {
	t.Errorf("Min #%d: got %d, want %d", i, got, want)
	}
	if got, want := set.Max(), wantMax[i]; got != want {
	t.Errorf("Max #%d: got %d, want %d", i, got, want)
	}
	}

	set.Insert(intsets.MinInt)
	if got, want := set.Min(), intsets.MinInt; got != want {
	t.Errorf("Min: got %d, want %d", got, want)
	}

	set.Insert(intsets.MaxInt)
	if got, want := set.Max(), intsets.MaxInt; got != want {
	t.Errorf("Max: got %d, want %d", got, want)
	}
	}

	func TestEquals(t *testing.T) {
	var setX intsets.Sparse
	setX.Insert(456)
	setX.Insert(123)
	setX.Insert(789)

	if !setX.Equals(&setX) {
	t.Errorf("Equals(%s, %s): got false", &setX, &setX)
	}

	var setY intsets.Sparse
	setY.Insert(789)
	setY.Insert(456)
	setY.Insert(123)

	if !setX.Equals(&setY) {
	t.Errorf("Equals(%s, %s): got false", &setX, &setY)
	}

	setY.Insert(1)
	if setX.Equals(&setY) {
	t.Errorf("Equals(%s, %s): got true", &setX, &setY)
	}

	var empty intsets.Sparse
	if setX.Equals(&empty) {
	t.Errorf("Equals(%s, %s): got true", &setX, &empty)
	}

	// Edge case: some block (with offset=0) appears in X but not Y.
	setY.Remove(123)
	if setX.Equals(&setY) {
	t.Errorf("Equals(%s, %s): got true", &setX, &setY)
	}
	}

	// A pset is a parallel implementation of a set using both an intsets.Sparse
	// and a built-in hash map.
	type pset struct {
	hash map[int]bool
	bits intsets.Sparse
	}

	func makePset() *pset {
	return &pset{hash: make(map[int]bool)}
	}

	func (set *pset) add(n int) {
	prev := len(set.hash)
	set.hash[n] = true
	grewA := len(set.hash) > prev

	grewB := set.bits.Insert(n)

	if grewA != grewB {
	panic(fmt.Sprintf("add(%d): grewA=%t grewB=%t", n, grewA, grewB))
	}
	}

	func (set *pset) remove(n int) {
	prev := len(set.hash)
	delete(set.hash, n)
	shrankA := len(set.hash) < prev

	shrankB := set.bits.Remove(n)

	if shrankA != shrankB {
	panic(fmt.Sprintf("remove(%d): shrankA=%t shrankB=%t", n, shrankA, shrankB))
	}
	}

	func (set pset) check(t testing.T, msg string) {
	var eltsA []int
	for elt := range set.hash {
	eltsA = append(eltsA, int(elt))
	}
	sort.Ints(eltsA)

	eltsB := set.bits.AppendTo(nil)

	if a, b := fmt.Sprint(eltsA), fmt.Sprint(eltsB); a != b {
	t.Errorf("check(%s): hash=%s bits=%s (%s)", msg, a, b, &set.bits)
	}

	if err := set.bits.Check(); err != nil {
	t.Fatalf("Check(%s): %s: %#v", msg, err, &set.bits)
	}
	}

	// randomPset returns a parallel set of random size and elements.
	func randomPset(prng rand.Rand, maxSize int) pset {
	set := makePset()
	size := int(prng.Int()) % maxSize
	for i := 0; i < size; i++ {
	// TODO(adonovan): benchmark how performance varies
	// with this sparsity parameter.
	n := int(prng.Int()) % 10000
	set.add(n)
	}
	return set
	}

	// TestRandomMutations performs the same random adds/removes on two
	// set implementations and ensures that they compute the same result.
	func TestRandomMutations(t *testing.T) {
	const debug = false

	set := makePset()
	prng := rand.New(rand.NewSource(0))
	for i := 0; i < 10000; i++ {
	n := int(prng.Int())%2000 - 1000
	if i%2 == 0 {
	if debug {
	log.Printf("add %d", n)
	}
	set.add(n)
	} else {
	if debug {
	log.Printf("remove %d", n)
	}
	set.remove(n)
	}
	if debug {
	set.check(t, "post mutation")
	}
	}
	set.check(t, "final")
	if debug {
	log.Print(&set.bits)
	}
	}

	func TestLowerBound(t *testing.T) {
	// Use random sets of sizes from 0 to about 4000.
	prng := rand.New(rand.NewSource(0))
	for i := uint(0); i < 12; i++ {
	x := randomPset(prng, 1<<i)
	for j := 0; j < 10000; j++ {
	found := intsets.MaxInt
	for e := range x.hash {
	if e >= j && e < found {
	found = e
	}
	}
	if res := x.bits.LowerBound(j); res != found {
	t.Errorf("%s: LowerBound(%d)=%d, expected %d", &x.bits, j, res, found)
	}
	}
	}
	}

	// TestSetOperations exercises classic set operations: ∩ , ∪, \.
	func TestSetOperations(t *testing.T) {
	prng := rand.New(rand.NewSource(0))

	// Use random sets of sizes from 0 to about 4000.
	// For each operator, we test variations such as
	// Z.op(X, Y), Z.op(X, Z) and Z.op(Z, Y) to exercise
	// the degenerate cases of each method implementation.
	for i := uint(0); i < 12; i++ {
	X := randomPset(prng, 1<<i)
	Y := randomPset(prng, 1<<i)

	// TODO(adonovan): minimise dependencies between stanzas below.

	// Copy(X)
	C := makePset()
	C.bits.Copy(&Y.bits) // no effect on result
	C.bits.Copy(&X.bits)
	C.hash = X.hash
	C.check(t, "C.Copy(X)")
	C.bits.Copy(&C.bits)
	C.check(t, "C.Copy(C)")

	// U.Union(X, Y)
	U := makePset()
	U.bits.Union(&X.bits, &Y.bits)
	for n := range X.hash {
	U.hash[n] = true
	}
	for n := range Y.hash {
	U.hash[n] = true
	}
	U.check(t, "U.Union(X, Y)")

	// U.Union(X, X)
	U.bits.Union(&X.bits, &X.bits)
	U.hash = X.hash
	U.check(t, "U.Union(X, X)")

	// U.Union(U, Y)
	U = makePset()
	U.bits.Copy(&X.bits)
	U.bits.Union(&U.bits, &Y.bits)
	for n := range X.hash {
	U.hash[n] = true
	}
	for n := range Y.hash {
	U.hash[n] = true
	}
	U.check(t, "U.Union(U, Y)")

	// U.Union(X, U)
	U.bits.Copy(&Y.bits)
	U.bits.Union(&X.bits, &U.bits)
	U.check(t, "U.Union(X, U)")

	// U.UnionWith(U)
	U.bits.UnionWith(&U.bits)
	U.check(t, "U.UnionWith(U)")

	// I.Intersection(X, Y)
	I := makePset()
	I.bits.Intersection(&X.bits, &Y.bits)
	for n := range X.hash {
	if Y.hash[n] {
	I.hash[n] = true
	}
	}
	I.check(t, "I.Intersection(X, Y)")

	// I.Intersection(X, X)
	I.bits.Intersection(&X.bits, &X.bits)
	I.hash = X.hash
	I.check(t, "I.Intersection(X, X)")

	// I.Intersection(I, X)
	I.bits.Intersection(&I.bits, &X.bits)
	I.check(t, "I.Intersection(I, X)")

	// I.Intersection(X, I)
	I.bits.Intersection(&X.bits, &I.bits)
	I.check(t, "I.Intersection(X, I)")

	// I.Intersection(I, I)
	I.bits.Intersection(&I.bits, &I.bits)
	I.check(t, "I.Intersection(I, I)")

	// D.Difference(X, Y)
	D := makePset()
	D.bits.Difference(&X.bits, &Y.bits)
	for n := range X.hash {
	if !Y.hash[n] {
	D.hash[n] = true
	}
	}
	D.check(t, "D.Difference(X, Y)")

	// D.Difference(D, Y)
	D.bits.Copy(&X.bits)
	D.bits.Difference(&D.bits, &Y.bits)
	D.check(t, "D.Difference(D, Y)")

	// D.Difference(Y, D)
	D.bits.Copy(&X.bits)
	D.bits.Difference(&Y.bits, &D.bits)
	D.hash = make(map[int]bool)
	for n := range Y.hash {
	if !X.hash[n] {
	D.hash[n] = true
	}
	}
	D.check(t, "D.Difference(Y, D)")

	// D.Difference(X, X)
	D.bits.Difference(&X.bits, &X.bits)
	D.hash = nil
	D.check(t, "D.Difference(X, X)")

	// D.DifferenceWith(D)
	D.bits.Copy(&X.bits)
	D.bits.DifferenceWith(&D.bits)
	D.check(t, "D.DifferenceWith(D)")

	// SD.SymmetricDifference(X, Y)
	SD := makePset()
	SD.bits.SymmetricDifference(&X.bits, &Y.bits)
	for n := range X.hash {
	if !Y.hash[n] {
	SD.hash[n] = true
	}
	}
	for n := range Y.hash {
	if !X.hash[n] {
	SD.hash[n] = true
	}
	}
	SD.check(t, "SD.SymmetricDifference(X, Y)")

	// X.SymmetricDifferenceWith(Y)
	SD.bits.Copy(&X.bits)
	SD.bits.SymmetricDifferenceWith(&Y.bits)
	SD.check(t, "X.SymmetricDifference(Y)")

	// Y.SymmetricDifferenceWith(X)
	SD.bits.Copy(&Y.bits)
	SD.bits.SymmetricDifferenceWith(&X.bits)
	SD.check(t, "Y.SymmetricDifference(X)")

	// SD.SymmetricDifference(X, X)
	SD.bits.SymmetricDifference(&X.bits, &X.bits)
	SD.hash = nil
	SD.check(t, "SD.SymmetricDifference(X, X)")

	// SD.SymmetricDifference(X, Copy(X))
	X2 := makePset()
	X2.bits.Copy(&X.bits)
	SD.bits.SymmetricDifference(&X.bits, &X2.bits)
	SD.check(t, "SD.SymmetricDifference(X, Copy(X))")

	// Copy(X).SymmetricDifferenceWith(X)
	SD.bits.Copy(&X.bits)
	SD.bits.SymmetricDifferenceWith(&X.bits)
	SD.check(t, "Copy(X).SymmetricDifferenceWith(X)")
	}
	}

	func TestIntersectionWith(t *testing.T) {
	// Edge cases: the pairs (1,1), (1000,2000), (8000,4000)
	// exercise the <, >, == cases in IntersectionWith that the
	// TestSetOperations data is too dense to cover.
	var X, Y intsets.Sparse
	X.Insert(1)
	X.Insert(1000)
	X.Insert(8000)
	Y.Insert(1)
	Y.Insert(2000)
	Y.Insert(4000)
	X.IntersectionWith(&Y)
	if got, want := X.String(), "{1}"; got != want {
	t.Errorf("IntersectionWith: got %s, want %s", got, want)
	}
	}

	func TestIntersects(t *testing.T) {
	prng := rand.New(rand.NewSource(0))

	for i := uint(0); i < 12; i++ {
	X, Y := randomPset(prng, 1<<i), randomPset(prng, 1<<i)
	x, y := &X.bits, &Y.bits

	// test the slow way
	var z intsets.Sparse
	z.Copy(x)
	z.IntersectionWith(y)

	if got, want := x.Intersects(y), !z.IsEmpty(); got != want {
	t.Errorf("Intersects(%s, %s): got %v, want %v (%s)", x, y, got, want, &z)
	}

	// make it false
	a := x.AppendTo(nil)
	for _, v := range a {
	y.Remove(v)
	}

	if got, want := x.Intersects(y), false; got != want {
	t.Errorf("Intersects: got %v, want %v", got, want)
	}

	// make it true
	if x.IsEmpty() {
	continue
	}
	i := prng.Intn(len(a))
	y.Insert(a[i])

	if got, want := x.Intersects(y), true; got != want {
	t.Errorf("Intersects: got %v, want %v", got, want)
	}
	}
	}

	func TestSubsetOf(t *testing.T) {
	prng := rand.New(rand.NewSource(0))

	for i := uint(0); i < 12; i++ {
	X, Y := randomPset(prng, 1<<i), randomPset(prng, 1<<i)
	x, y := &X.bits, &Y.bits

	// test the slow way
	var z intsets.Sparse
	z.Copy(x)
	z.DifferenceWith(y)

	if got, want := x.SubsetOf(y), z.IsEmpty(); got != want {
	t.Errorf("SubsetOf: got %v, want %v", got, want)
	}

	// make it true
	y.UnionWith(x)

	if got, want := x.SubsetOf(y), true; got != want {
	t.Errorf("SubsetOf: got %v, want %v", got, want)
	}

	// make it false
	if x.IsEmpty() {
	continue
	}
	a := x.AppendTo(nil)
	i := prng.Intn(len(a))
	y.Remove(a[i])

	if got, want := x.SubsetOf(y), false; got != want {
	t.Errorf("SubsetOf: got %v, want %v", got, want)
	}
	}
	}

	func TestBitString(t *testing.T) {
	for _, test := range []struct {
	input []int
	want string
	}{
	{nil, "0"},
	{[]int{0}, "1"},
	{[]int{0, 4, 5}, "110001"},
	{[]int{0, 7, 177}, "1" + strings.Repeat("0", 169) + "10000001"},
	{[]int{-3, 0, 4, 5}, "110001.001"},
	{[]int{-3}, "0.001"},
	} {
	var set intsets.Sparse
	for _, x := range test.input {
	set.Insert(x)
	}
	if got := set.BitString(); got != test.want {
	t.Errorf("BitString(%s) = %s, want %s", set.String(), got, test.want)
	}
	}
	}

	func TestFailFastOnShallowCopy(t *testing.T) {
	var x intsets.Sparse
	x.Insert(1)

	y := x // shallow copy (breaks representation invariants)
	defer func() {
	got := fmt.Sprint(recover())
	want := "interface conversion: interface {} is nil, not intsets.to_copy_a_sparse_you_must_call_its_Copy_method"
	if got != want {
	t.Errorf("shallow copy: recover() = %q, want %q", got, want)
	}
	}()
	y.String() // panics
	t.Error("didn't panic as expected")
	}

	// -- Benchmarks -------------------------------------------------------

	// TODO(adonovan):
	// - Add benchmarks of each method.
	// - Gather set distributions from pointer analysis.
	// - Measure memory usage.

	func benchmarkInsertProbeSparse(b *testing.B, size, spread int) {
	prng := rand.New(rand.NewSource(0))
	// Generate our insertions and probes beforehand (we don't want to benchmark
	// the prng).
	insert := make([]int, size)
	probe := make([]int, size*2)
	for i := range insert {
	insert[i] = prng.Int() % spread
	}
	for i := range probe {
	probe[i] = prng.Int() % spread
	}

	b.ResetTimer()
	var x intsets.Sparse
	for tries := 0; tries < b.N; tries++ {
	x.Clear()
	for _, n := range insert {
	x.Insert(n)
	}
	hits := 0
	for _, n := range probe {
	if x.Has(n) {
	hits++
	}
	}
	// Use the variable so it doesn't get optimized away.
	if hits > len(probe) {
	b.Fatalf("%d hits, only %d probes", hits, len(probe))
	}
	}
	}

	func BenchmarkInsertProbeSparse_2_10(b *testing.B) {
	benchmarkInsertProbeSparse(b, 2, 10)
	}

	func BenchmarkInsertProbeSparse_10_10(b *testing.B) {
	benchmarkInsertProbeSparse(b, 10, 10)
	}

	func BenchmarkInsertProbeSparse_10_1000(b *testing.B) {
	benchmarkInsertProbeSparse(b, 10, 1000)
	}

	func BenchmarkInsertProbeSparse_100_100(b *testing.B) {
	benchmarkInsertProbeSparse(b, 100, 100)
	}

	func BenchmarkInsertProbeSparse_100_10000(b *testing.B) {
	benchmarkInsertProbeSparse(b, 100, 1000)
	}

	func BenchmarkUnionDifferenceSparse(b *testing.B) {
	prng := rand.New(rand.NewSource(0))
	for tries := 0; tries < b.N; tries++ {
	var x, y, z intsets.Sparse
	for i := 0; i < 1000; i++ {
	n := int(prng.Int()) % 100000
	if i%2 == 0 {
	x.Insert(n)
	} else {
	y.Insert(n)
	}
	}
	z.Union(&x, &y)
	z.Difference(&x, &y)
	}
	}

	func BenchmarkUnionDifferenceHashTable(b *testing.B) {
	prng := rand.New(rand.NewSource(0))
	for tries := 0; tries < b.N; tries++ {
	x, y, z := make(map[int]bool), make(map[int]bool), make(map[int]bool)
	for i := 0; i < 1000; i++ {
	n := int(prng.Int()) % 100000
	if i%2 == 0 {
	x[n] = true
	} else {
	y[n] = true
	}
	}
	// union
	for n := range x {
	z[n] = true
	}
	for n := range y {
	z[n] = true
	}
	// difference
	z = make(map[int]bool)
	for n := range y {
	if !x[n] {
	z[n] = true
	}
	}
	}
	}

	func BenchmarkAppendTo(b *testing.B) {
	prng := rand.New(rand.NewSource(0))
	var x intsets.Sparse
	for i := 0; i < 1000; i++ {
	x.Insert(int(prng.Int()) % 10000)
	}
	var space [1000]int
	for tries := 0; tries < b.N; tries++ {
	x.AppendTo(space[:0])
	}
	}