Thanks a lot for tracking this down. For reference, here it is in our bug
On Thursday, February 11, 2016 at 3:28:33 AM UTC-8, Ron Ben-Yosef wrote:
> I'm using the proto3 C++ library compiled in MSVC, and noticed some pretty
> strange behavior - using the JsonToBinaryString or JsonToBinaryStream
> functions, values in the upper half of the uint32 range get lost in the
> transition from JSON to binary.
> After some investigation, it seems the issue's root cause is in the
> MathUtil::Sign function (called from NumberConvertAndCheck, which is called
> from DataPiece::GenericConvert, which gets called
> from DataPiece::ToUint32...)
> When compiled in Release mode (with optimizations) it seems, the ternary
> condition operator in that function gets optimized incorrectly (the
> assembly code generated looks as if it's treated as int32 instead of
> uint32), causing the Sign function to return an incorrect result in the
> case of those larger uint32 values, which in turn causes a condition in
> some if statement in NumberConvertAndCheck to evaluate to false when it
> should be true, thus causing the value to be dropped.
> Now obviously this is not really a protobuf issue, but more likely a
> compiler bug (opened an issue regarding this with Microsoft
> but since it's likely to be a while until the compiler issue is addressed
> (if at all) and since protobuf does support MSVC compilers, I would suggest
> that until then the issue should probably be handled with a workaround in
> the protobuf code in the meantime, for instance by changing that ternary
> condition operator to a simple if-else statement (seems to compile
> correctly, without this issue), or simply removing optimization flags when
> compiling with VS2010/VS2012/VS2013/VS2015, although this is probably a
> less desirable solution.
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