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sort: fix for nondeterministic less function in quicksort pivot

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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>
This commit is contained in:
Jure Ham 2016-02-23 11:41:27 +01:00 committed by Ian Lance Taylor
parent 50c38d46e8
commit 38d4511b10
2 changed files with 44 additions and 7 deletions
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14
src/sort/sort.go
View File

@ -119,15 +119,15 @@ func doPivot(data Interface, lo, hi int) (midlo, midhi int) {
pivot := lo
a, c := lo+1, hi-1
for ; a != c && data.Less(a, pivot); a++ {
for ; a < c && data.Less(a, pivot); a++ {
}
b := a
for {
for ; b != c && !data.Less(pivot, b); b++ { // data[b] <= pivot
for ; b < c && !data.Less(pivot, b); b++ { // data[b] <= pivot
}
for ; b != c && data.Less(pivot, c-1); c-- { // data[c-1] > pivot
for ; b < c && data.Less(pivot, c-1); c-- { // data[c-1] > pivot
}
if b == c {
if b >= c {
break
}
// data[b] > pivot; data[c-1] <= pivot
@ -167,11 +167,11 @@ func doPivot(data Interface, lo, hi int) (midlo, midhi int) {
// data[a <= i < b] unexamined
// data[b <= i < c] = pivot
for {
for ; a != b && !data.Less(b-1, pivot); b-- { // data[b] == pivot
for ; a < b && !data.Less(b-1, pivot); b-- { // data[b] == pivot
}
for ; a != b && data.Less(a, pivot); a++ { // data[a] < pivot
for ; a < b && data.Less(a, pivot); a++ { // data[a] < pivot
}
if a == b {
if a >= b {
break
}
// data[a] == pivot; data[b-1] < pivot

37
src/sort/sort_test.go
View File

@ -109,6 +109,43 @@ func TestReverseSortIntSlice(t *testing.T) {
}
}
type nonDeterministicTestingData struct {
r *rand.Rand
}
func (t *nonDeterministicTestingData) Len() int {
return 500
}
func (t *nonDeterministicTestingData) Less(i, j int) bool {
if i < 0 || j < 0 || i >= t.Len() || j >= t.Len() {
panic("nondeterministic comparison out of bounds")
}
return t.r.Float32() < 0.5
}
func (t *nonDeterministicTestingData) Swap(i, j int) {
if i < 0 || j < 0 || i >= t.Len() || j >= t.Len() {
panic("nondeterministic comparison out of bounds")
}
}
func TestNonDeterministicComparison(t *testing.T) {
// Ensure that sort.Sort does not panic when Less returns inconsistent results.
// See https://golang.org/issue/14377.
defer func() {
if r := recover(); r != nil {
t.Error(r)
}
}()
td := &nonDeterministicTestingData{
r: rand.New(rand.NewSource(0)),
}
for i := 0; i < 10; i++ {
Sort(td)
}
}
func BenchmarkSortString1K(b *testing.B) {
b.StopTimer()
for i := 0; i < b.N; i++ {