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VM: double.parse creates NaN value not identical to double.NAN. #15293

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lrhn opened this issue Nov 25, 2013 · 4 comments
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VM: double.parse creates NaN value not identical to double.NAN. #15293

lrhn opened this issue Nov 25, 2013 · 4 comments
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@floitschG
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area-vm Use area-vm for VM related issues, including code coverage, FFI, and the AOT and JIT backends. closed-as-intended Closed as the reported issue is expected behavior

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@lrhn
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lrhn commented Nov 25, 2013

Example code:
main() {
  print(identical(double.NAN, double.parse("NAN")));
}

prints "false", should print "true".

I'm adding a hack to prevent this problem, in double_patch.dart,
adding the line:
  if (result.isNaN) return NAN;

That's a workaround, but the underlying identical operation should not make this necessary, and it suggests that it may happen in other places too.
See: https://codereview.chromium.org/85633003/diff/50001/runtime/lib/double_patch.dart
@ghost
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ghost commented Nov 25, 2013

Set owner to @sgmitrovic.
Added Accepted label.

@iposva-google
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After some discussion we are not sure that identical for Nan and -Nan is expected and desired. Similarly are two Nan values with a different bit pattern identical?

cc @sgmitrovic.
Set owner to @floitschG.
Added NeedsInfo label.

@lrhn
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lrhn commented Nov 26, 2013

From the spec (section: Object Identity):

"The predefined dart function identical() is defined such that identical(c1, c2) iff:
  ...
  c1 and c2 are instances of double and one of the following holds:
     ...
     Both c1 and c2 represent a NaN value."

So all NaN values need to be identical.

@floitschG
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I filed issue #15317.

Closing this issue as designed.

Added AsDesigned label.

@lrhn lrhn added Type-Defect area-vm Use area-vm for VM related issues, including code coverage, FFI, and the AOT and JIT backends. closed-as-intended Closed as the reported issue is expected behavior labels Nov 26, 2013
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area-vm Use area-vm for VM related issues, including code coverage, FFI, and the AOT and JIT backends. closed-as-intended Closed as the reported issue is expected behavior
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