So the initialization of the mersenne twister is expensive, so if you do it once and then reuse it, it is much more efficient than going to Wincrypt.
Mersenne is only fast on x86/x64. It is dog slow on every other CPU. Also, I hate to be pedantic, but Mersenne is not cryptographically secure. UUIDs ought to be generated from a crypto-strong source unless the end user specifically asks for otherwise. On Windows, that's RtlGenRandom() which is rand_s() in recent MSVC's. On POSIX that is /dev/urandom or /dev/random depending on the POSIX flavour. If you want something faster, Blake2b is crypto strong and fast on all modern CPUs. Just need to seed it with a random seed, and you're happy. Failing that, really recent CPUs can do SHA256 in hardware, but they have tiny market penetration currently. You can, of course, use any AES hardware offload also as a randomness generator, that has much wider support in CPUs. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/