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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