On Friday, 20 July 2012 at 12:51:25 UTC, Andrea Fontana wrote: > CMWC is proven to be a valid method and it passes diehard > tests. It was > written by prof. George Marsiglia (he developed xorshift too - > included > in std.random). He was one of the best experts in PRNG. > > He also developed the "Marsiglia's Theorem" where he > demonstrate that > LCG (that is the default algorithm for many languages for ex: > glibc and > vc++ lib, ...) has big issues. > LCG is very widespread but d doesn't use it (phew!). If a user > know > difference between PRNG algorithms can use MT, but as default > for people > that use weak C rand() function as default (that neither passes > diehard > tests) it can just be a good improvement (why should we give > them MT > that is slower than CMWC if they neither know default rand() > weakness?) > > MT has a complex implementation, I hope std.random MT was > tested :) > > Il giorno ven, 20/07/2012 alle 13.16 +0200, monarch_dodra ha > scritto: > >> On Friday, 20 July 2012 at 09:47:52 UTC, Andrea Fontana wrote: >> > I read that default RNG in phobos is Mersenne Twister. >> > >> > I think it would be a good idea to replace it with >> > complementary-multiply-with-carry (cmwc). CMWC is faster >> > (use simpler >> > math), has a longer period (standard implementation has a >> > 2^131104 >> > period vs 2^19937 of current MT implementation in phobos) >> > and passed >> > diehard tests (mt passes them too) >> > >> > And of course it's very easy to implement: >> > http://en.wikipedia.org/wiki/Multiply-with-carry#Implementation >> >> I'd say the problem is that it is not a very widespread or >> known PRNG. >> >> While I wouldn't be against adding it to the library ("I see >> no reason not to add it"), making it the _default_ PRNG is a >> whole other story. >> >> Users that choose "default" want something reliable, >> documented, trustworthy etc... >> >> Multiply With Carry seems like it is Cutting Edge to me, not >> yet widespread, known or tested. I'd say it should only be >> used by those that explicitly request it's usage. But Mersenne Twister has a cooler name :o) 'Multiply with carry' is so blah. You'll need to come up with a sexy new name for it. Cheers, Craig