Hi Everyone, Currently we are determining cpu feature by trying to execute an instruction, and catching a SIGILL. It has been part of the library as long as I can remember.
I checked in some code on my testing fork that uses getauxvalue(3) on Linux and Android to query the runtime for features. One of the reasons I avoided it in the past was, its not documented well. The Glibc folks recently answered some questions for us, so we know how to handle Aarch32 and Aarch64. Also see "When to use AT_HWCAP or AT_HWCAP2", https://sourceware.org/ml/libc-help/2017-08/msg00012.html. We fall back to CPU probing if we can't find an alternate or approved implementation. We need something for the BSDs and Apple. I believe the BSDs provide sysctl, but its not clear to me what Apple "officially" uses on iOS and OS X. iOS is very important because of acceleration on the smartphones and tablets. Apple is critical because their signal handling/longjump stuff appears broken. Uri and I had troubles with it last year or so. And OpenSSL recently moved away from the probes on Apple platforms because of unexplained crashes after a SIGILL. An interesting footnote is, some benchmarks sped-up by 0.1 cpb. I'm guessing its related to spatial and temporal locality of code and data. Its a lot easier to test a flag in a bitmask vector; and invoking a signal handler is expensive. You can see what the code looks like at https://github.com/noloader/cryptopp/blob/master/rijndael-simd.cpp#L106 and https://github.com/noloader/cryptopp/blob/master/neon.cpp#L75. Jeff -- -- You received this message because you are subscribed to the "Crypto++ Users" Google Group. To unsubscribe, send an email to cryptopp-users-unsubscr...@googlegroups.com. More information about Crypto++ and this group is available at http://www.cryptopp.com. --- You received this message because you are subscribed to the Google Groups "Crypto++ Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to cryptopp-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
