overflow-arith: begin to add support for overflow builtin functions
The idea of the overflow-arith.h header is to collect overflow checking functions in one central place. If gcc compiler supports the __builtin_overflow_* builtins we use them because they might give better performance, otherwise the code falls back to normal overflow checking functions. The builtin_overflow functions are supported by gcc-5 and clang. The matter of supporting clang is to just provide a corresponding CC_HAVE_BUILTIN_OVERFLOW, because the specific overflow checking builtins don't differ between gcc and clang. I just provide overflow_usub function here as I intend this to get merged into net, more functions will definitely follow as they are needed. Signed-off-by:Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by:
David S. Miller <davem@davemloft.net>
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c80dbe04
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