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cmp/internal/value: fix handling of negative zero for floats #152

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merged 2 commits into from
Aug 5, 2019
Merged

cmp/internal/value: fix handling of negative zero for floats #152

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68cd567
cmp/internal/value: fix handling of negative zero for floats
dsnet Aug 5, 2019
cefcd77
Merge branch 'master' into fix-float-zero
dsnet Aug 5, 2019
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4 changes: 3 additions & 1 deletion cmp/internal/value/sort.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ func SortKeys(vs []reflect.Value) []reflect.Value {
}

// Sort the map keys.
sort.Slice(vs, func(i, j int) bool { return isLess(vs[i], vs[j]) })
sort.SliceStable(vs, func(i, j int) bool { return isLess(vs[i], vs[j]) })

// Deduplicate keys (fails for NaNs).
vs2 := vs[:1]
Expand All @@ -42,6 +42,8 @@ func isLess(x, y reflect.Value) bool {
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return x.Uint() < y.Uint()
case reflect.Float32, reflect.Float64:
// NOTE: This does not sort -0 as less than +0
// since Go maps treat -0 and +0 as equal keys.
fx, fy := x.Float(), y.Float()
return fx < fy || math.IsNaN(fx) && !math.IsNaN(fy)
case reflect.Complex64, reflect.Complex128:
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9 changes: 6 additions & 3 deletions cmp/internal/value/zero.go
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Expand Up @@ -4,7 +4,10 @@

package value

import "reflect"
import (
"math"
"reflect"
)

// IsZero reports whether v is the zero value.
// This does not rely on Interface and so can be used on unexported fields.
Expand All @@ -17,9 +20,9 @@ func IsZero(v reflect.Value) bool {
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return v.Uint() == 0
case reflect.Float32, reflect.Float64:
return v.Float() == 0
return math.Float64bits(v.Float()) == 0
case reflect.Complex64, reflect.Complex128:
return v.Complex() == 0
return math.Float64bits(real(v.Complex())) == 0 && math.Float64bits(imag(v.Complex())) == 0
case reflect.String:
return v.String() == ""
case reflect.UnsafePointer:
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7 changes: 7 additions & 0 deletions cmp/internal/value/zero_test.go
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Expand Up @@ -6,6 +6,7 @@ package value

import (
"archive/tar"
"math"
"reflect"
"testing"
)
Expand All @@ -32,6 +33,12 @@ func TestIsZero(t *testing.T) {
{TestIsZero, false},
{[...]int{0, 0, 0}, true},
{[...]int{0, 1, 0}, false},
{math.Copysign(0, +1), true},
{math.Copysign(0, -1), false},
{complex(math.Copysign(0, +1), math.Copysign(0, +1)), true},
{complex(math.Copysign(0, -1), math.Copysign(0, +1)), false},
{complex(math.Copysign(0, +1), math.Copysign(0, -1)), false},
{complex(math.Copysign(0, -1), math.Copysign(0, -1)), false},
}

for _, tt := range tests {
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