On 21.10.2011. 13:06, Tim Blechmann wrote:
compile-time vs run-time dispatching: some instructions are not available on every CPU of a specific architecture. e.g. cmpxchg8b or cmpxchg16b are not available on all ia32/x86_64 cpus. i would appreciate if these instructions would not be used before performing a CPUID check, whether these instructions are really available (at least in a legacy mode)
the correct way to do that is to have different libraries for sub-architectures and have the runtime- linker decide... this requires infrastructure not present in boost
it would be equally correct to have something like: static bool has_cmpxchg16b = query_cpuid_for_cmpxchg16b()
if (has_cmpxchg16b) use_cmpxchg16b(); else use_fallback();
less bloat and prbly only a minor performance hit ;)
cmpxchg8b is available since the original Pentium. Preferably dynamic support for such ancient hardware, if supported at all, should not be on by default (by forcing dynamic dispatching on everyone). -- "What Huxley teaches is that in the age of advanced technology, spiritual devastation is more likely to come from an enemy with a smiling face than from one whose countenance exudes suspicion and hate." Neil Postman