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

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

diff --git a/src/pkg/sort/sort.go b/src/pkg/sort/sort.go
index 067d27901e44aab9fbfff271668f7a14c82e28c5..0a4a4375f05910f849b778fe610edf0084d3418c 100644 (file)
--- a/src/pkg/sort/sort.go
+++ b/src/pkg/sort/sort.go
@@ -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.

diff --git a/src/pkg/sort/sort_test.go b/src/pkg/sort/sort_test.go
index 64d486b7590dffa584428b7b69b6ca16c2cb465e..5007a92a56267689be54144a1cc73a9861876ef4 100644 (file)
--- a/src/pkg/sort/sort_test.go
+++ b/src/pkg/sort/sort_test.go
@@ -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) {