在 2021/4/12 上午10:46, He Leon via Gcc-help 写道:
I meet an issue of integral promotion. I have small APP as appended. The bit-fields integral promotion(***shift = fl_a.e << 28***) result is different between Linux and windows. a) Linux gcc: fl_a.e is promoted as integer, and shift result is "0xffffffffe0000000", b) windows: fl_a.e is promoted as unsigned integer, and shift result is "0x7e0000000" Per C++ spec, seems Linux behavior is correct.
It is not Windows that is incorrect; it is MSVC that is incorrect, because if you compile this piece of code with mingw-w64 GCC, you will get the correct result.
Not only is there no option to change this behavior, your code also results in an overflow (because `fl_a.e` has type `int` which comprises 32 bits) which is undefined behavior.
`-Wsign-conversion` may help you catch such issues, but you probably have to change your code. -- Best regards, Liu Hao
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