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sort: fix for nondeterministic less function in quicksort pivot
Fixes #14377 Change-Id: I130a6e1b8bc827db44efd0a74e759b894ecc4977 Reviewed-on: https://go-review.googlesource.com/19823 Reviewed-by: Ian Lance Taylor <iant@golang.org> Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>
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@ -119,15 +119,15 @@ func doPivot(data Interface, lo, hi int) (midlo, midhi int) {
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pivot := lo
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a, c := lo+1, hi-1
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for ; a != c && data.Less(a, pivot); a++ {
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for ; a < c && data.Less(a, pivot); a++ {
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}
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b := a
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for {
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for ; b != c && !data.Less(pivot, b); b++ { // data[b] <= pivot
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for ; b < c && !data.Less(pivot, b); b++ { // data[b] <= pivot
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}
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for ; b != c && data.Less(pivot, c-1); c-- { // data[c-1] > pivot
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for ; b < c && data.Less(pivot, c-1); c-- { // data[c-1] > pivot
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}
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if b == c {
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if b >= c {
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break
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}
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// data[b] > pivot; data[c-1] <= pivot
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@ -167,11 +167,11 @@ func doPivot(data Interface, lo, hi int) (midlo, midhi int) {
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// data[a <= i < b] unexamined
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// data[b <= i < c] = pivot
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for {
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for ; a != b && !data.Less(b-1, pivot); b-- { // data[b] == pivot
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for ; a < b && !data.Less(b-1, pivot); b-- { // data[b] == pivot
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}
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for ; a != b && data.Less(a, pivot); a++ { // data[a] < pivot
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for ; a < b && data.Less(a, pivot); a++ { // data[a] < pivot
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}
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if a == b {
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if a >= b {
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break
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}
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// data[a] == pivot; data[b-1] < pivot
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@ -109,6 +109,43 @@ func TestReverseSortIntSlice(t *testing.T) {
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}
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}
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type nonDeterministicTestingData struct {
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r *rand.Rand
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}
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func (t *nonDeterministicTestingData) Len() int {
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return 500
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}
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func (t *nonDeterministicTestingData) Less(i, j int) bool {
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if i < 0 || j < 0 || i >= t.Len() || j >= t.Len() {
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panic("nondeterministic comparison out of bounds")
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}
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return t.r.Float32() < 0.5
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}
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func (t *nonDeterministicTestingData) Swap(i, j int) {
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if i < 0 || j < 0 || i >= t.Len() || j >= t.Len() {
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panic("nondeterministic comparison out of bounds")
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}
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}
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func TestNonDeterministicComparison(t *testing.T) {
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// Ensure that sort.Sort does not panic when Less returns inconsistent results.
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// See https://golang.org/issue/14377.
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defer func() {
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if r := recover(); r != nil {
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t.Error(r)
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}
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}()
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td := &nonDeterministicTestingData{
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r: rand.New(rand.NewSource(0)),
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}
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for i := 0; i < 10; i++ {
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Sort(td)
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}
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}
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func BenchmarkSortString1K(b *testing.B) {
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b.StopTimer()
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for i := 0; i < b.N; i++ {
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