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The literal "0" is treated as a signed int, which results in the expression "~0 << ..." performing a left shift of a negative number. This is undefined behaviour in C which newer GCC and Clang will warn about with -Wshift-negative-value. This commit uses unsigned long literals to ensure the shifts are interpreted correctly. For the record, all the compilers I have on hand handle this code correctly, but other compilers may not.
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Not only that but he uses |
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Very handy utility @clementine-m, thanks for writing this! I came across the following while building with a recent Clang.
The literal
0is treated as a signed int, which results in the expression~0 << ...performing a left shift of a negative number. This is undefinedbehaviour in C which newer GCC and Clang will warn about with
-Wshift-negative-value. This commit uses unsigned long literals to ensure the
shifts are interpreted correctly. For the record, all the compilers I have on
hand handle this code correctly, but other compilers may not.