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sort: fixed bug in (Float64Slice) Less; NaN less than anything else

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Previously comparisons with NaN led to contradictory results if it was
compared to anything not NaN, since Less always returned false, thus
breaking monotonicity of ordering.
This fix makes NaN less than anything else and adds NaN and (+-)Inf to
testcases.

Fixes #2092.

R=golang-dev, r, rsc, r
CC=golang-dev
https://golang.org/cl/4805051
This commit is contained in:
Florian Uekermann 2011-07-23 15:47:06 -04:00 committed by Russ Cox
parent 47410a2490
commit 480ef72c23
2 changed files with 5 additions and 2 deletions
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4
src/pkg/sort/sort.go
View File

@ -6,6 +6,8 @@
// collections.
package sort
import "math"
// A type, typically a collection, that satisfies sort.Interface can be
// sorted by the routines in this package. The methods require that the
// elements of the collection be enumerated by an integer index.
@ -167,7 +169,7 @@ func (p IntSlice) Sort() { Sort(p) }
type Float64Slice []float64
func (p Float64Slice) Len() int { return len(p) }
func (p Float64Slice) Less(i, j int) bool { return p[i] < p[j] }
func (p Float64Slice) Less(i, j int) bool { return p[i] < p[j] || math.IsNaN(p[i]) && !math.IsNaN(p[j]) }
func (p Float64Slice) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
// Sort is a convenience method.

3
src/pkg/sort/sort_test.go
View File

@ -6,6 +6,7 @@ package sort_test
import (
"fmt"
"math"
"rand"
. "sort"
"strconv"
@ -13,7 +14,7 @@ import (
)
var ints = [...]int{74, 59, 238, -784, 9845, 959, 905, 0, 0, 42, 7586, -5467984, 7586}
var float64s = [...]float64{74.3, 59.0, 238.2, -784.0, 2.3, 9845.768, -959.7485, 905, 7.8, 7.8}
var float64s = [...]float64{74.3, 59.0, math.Inf(1), 238.2, -784.0, 2.3, math.NaN(), math.NaN(), math.Inf(-1), 9845.768, -959.7485, 905, 7.8, 7.8}
var strings = [...]string{"", "Hello", "foo", "bar", "foo", "f00", "%*&^*&^&", "***"}
func TestSortIntSlice(t *testing.T) {