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reflect: when Converting between float32s, don't lose signal NaNs
When converting from float32->float64->float32, any signal NaNs get converted to quiet NaNs. Avoid that so using reflect.Value.Convert between two float32 types keeps the signal bit of NaNs. Update #36400 Change-Id: Ic4dd04c4be7189d2171d12b7e4e8f7cf2fb22bb4 Reviewed-on: https://go-review.googlesource.com/c/go/+/213497 Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>
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@ -4163,6 +4163,17 @@ func TestConvert(t *testing.T) {
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}
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}
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func TestConvertNaNs(t *testing.T) {
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const snan uint32 = 0x7f800001
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type myFloat32 float32
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x := V(myFloat32(math.Float32frombits(snan)))
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y := x.Convert(TypeOf(float32(0)))
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z := y.Interface().(float32)
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if got := math.Float32bits(z); got != snan {
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t.Errorf("signaling nan conversion got %x, want %x", got, snan)
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}
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}
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type ComparableStruct struct {
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X int
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}
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@ -2541,6 +2541,14 @@ func makeFloat(f flag, v float64, t Type) Value {
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return Value{typ, ptr, f | flagIndir | flag(typ.Kind())}
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}
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// makeFloat returns a Value of type t equal to v, where t is a float32 type.
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func makeFloat32(f flag, v float32, t Type) Value {
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typ := t.common()
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ptr := unsafe_New(typ)
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*(*float32)(ptr) = v
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return Value{typ, ptr, f | flagIndir | flag(typ.Kind())}
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}
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// makeComplex returns a Value of type t equal to v (possibly truncated to complex64),
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// where t is a complex64 or complex128 type.
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func makeComplex(f flag, v complex128, t Type) Value {
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@ -2613,6 +2621,12 @@ func cvtUintFloat(v Value, t Type) Value {
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// convertOp: floatXX -> floatXX
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func cvtFloat(v Value, t Type) Value {
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if v.Type().Kind() == Float32 && t.Kind() == Float32 {
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// Don't do any conversion if both types have underlying type float32.
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// This avoids converting to float64 and back, which will
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// convert a signaling NaN to a quiet NaN. See issue 36400.
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return makeFloat32(v.flag.ro(), *(*float32)(v.ptr), t)
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}
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return makeFloat(v.flag.ro(), v.Float(), t)
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}
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