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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