On Mon, 25 Apr 2016, Jonathan Lennox wrote: > Is there any portable way in GCC to detect whether the architecture we’re > targeting has a fast native 64-bit type? > > The motivation is that there are operations that it’s faster to do as a > single 64-bit multiplication if the architecture really supports native > 64-bit operations, but if instead 64-bit is emulated, it’s faster to write > multiple 32-bit multiplications. > [snip] > I know there are any number of 64-bit platforms that have x32-style ABIs. > Rather than enumerate them all, is there some way I can get this information > from GCC directly? (Extra points if it works on Clang as well.) As an approximation, you can use availability of non-standard integer type __int128 to infer whether 64-bit operations are native or not. Of course it doesn't guarantee that 64-bit paths would be faster than 32-bit paths, but chaining on exceptions to that should be easier. So something like: #ifdef __SIZEOF_INT128__ /* use 64-bit arith */ #else /* 32-bit */ #endif (__int128 is a GNU extension also supported by Clang) HTH. Alexander
