On Thu, Jun 22, 2017 at 12:34 PM, Toebs Douglass <toby@xxxxxxxxxxxxxx> wrote: > > I asked recently about the largest supported alignment. > > Turns out there is a compiler defined define, "__BIGGEST_ALIGNMENT", > which indicates this value. It is usually small (16 bytes kindafing). Its 32 for machines with AVX. > It seems to have in older versions (something like 4.5 ish and earlier) > to have been named "BIGGEST_ALIGNMENT". > > In other news, I've been experimenting again with the "__i686" define. > > As far as I can tell, it is defined for arch "i686" up to and including > "pentium3" (I'm currently using 5.4.0). > > https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gcc/x86-Options.html#x86-Options Also see https://gcc.gnu.org/onlinedocs/cpp/Predefined-Macros.html and https://gcc.gnu.org/onlinedocs/cpp/System-specific-Predefined-Macros.html#System-specific-Predefined-Macros. And from https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html : GCC also provides a target specific macro __BIGGEST_ALIGNMENT__, which is the largest alignment ever used for any data type on the target machine you are compiling for. For example, you could write: short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__))); Jeff
