Hej, all. Just to say what was done in the end, since it might help future archive readers. I'm now using __i386__ to detect and only 32-bit. Beyond detecting 32-bit I don't think I can tell which processor I'm on, from the compiler predefines. What I then turn to however are the __GCC_HAVE_SYNC_COMPARE_AND_SWAP_N predefines. I use __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 as a proxy for being an i486 or better (i386 lacks atomic operations). Additionally, when __x86_64__ is defined, I then use __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 to let me know if 128-bit CAS is available (as some very early Opterons do not have it, and I can deal with its absence gracefully and for free, so why not).
