On 16/07/18 21:52, Marcel Keller wrote: > Hi, > > I've found that the attached program, which supposedly adds 1 and 0 as > 128-bit numbers using inline assembly, outputs 2^64 + 1 instead when > compiled with g++ 7 or 8 and at least -O1. Am I doing something wrong, > or is this a compiler bug? > If you just want to use 128-bit integers, rather than learning inline assembly, then you might be easier using gcc's __int128 or unsigned __int128 types. If your particular target does not support __int128, then another option is the builtin overflow functions. With a little care (and optimisation enabled), these will give you at least as good code, and sometimes better, as your inline assembly. (It can be better because the compiler knows what they do for optimisation, and may be able to improve instruction scheduling.) <https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html>
