https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94087
--- Comment #20 from rguenther at suse dot de <rguenther at suse dot de> --- On Thu, 14 May 2020, redi at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94087 > > --- Comment #19 from Jonathan Wakely <redi at gcc dot gnu.org> --- > If you mean the mersenne twister in the std::random_device object, that's a > union member and doesn't exist when a proper source (/dev/random, rdrand, > rdseed etc) is available. So we'd need to add *another* mersenne twister > object > (which would double the size of std::random_device, changing ABI, or have to > be > global and protected by a mutex, or thread-local) and we'd have to seed it so > it's not 100% deterministic, and MT has a state size of 19968 bits which needs > a lot of seeding. It's not a good choice for many reasons. Doh. OK, guess I'd set up the twister in all cases and make it programatically skip itself when rdrand/rdseed is available so we could easily fall back to it. Not sure what extra state there is that warrants the union, but well ... I suppose simply calling random() from the C library isn't an option ;)
