it would be great to move to pcg. careful implementation here: https://github.com/MichaelTJones/pcg
extensive use for quite a while On Sun, Oct 29, 2017 at 10:11 AM, <ra...@develer.com> wrote: > Il giorno domenica 29 ottobre 2017 17:49:39 UTC+1, T L ha scritto: >> >> >> >> On Sunday, October 29, 2017 at 3:47:43 AM UTC-4, Sokolov Yura wrote: >>> >>> Why no one writes Go's version they've tested with? >>> >>> HEAD of master branch is uniform? >>> >> >> 1.9.2 is a little unfair. Tip is fair. >> > > Let me recap what happened. > > At some point during the 1.9 cycle, fastrandn() was changed to use a > multiplication+shift for doing a reduction, which is much faster and has > introduces zero bias compared to a modulus which is much slower and > potentially adds a little bias. > > Unfortunately, the underlying generator used by fastrand (a LFSR) was very > weak and had a lot of bias in the high bits. Low bits were "acceptable" so > using modulus was kind of acceptable in fastrandn(), and select was "fair > enough". After switching to multiplication, select became were unfair. > After this was reported, the generator was changed on tip to use > xorshift32+ with 64-bit state, which is much much stronger (passes > SmallCrush, for instance), and thus fixes the unfairness in select for > good, whatever reduction is used. To avoid regressions, the new generator > wasn't backported to 1.9.2, but instead the fastrandn() multiplication > change was reverted. > > So to recap: > > up to 1.8: LFSR+modulus => select is "fair enough" > 1.9.0 / 1.9.1: LFSR+multiplication => select is very unfair > 1.9.2: LFSR+modulus => select is "fair enough" (same as 1.8) > tip: xorshift32+multiplication => select is fair > > Giovanni > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- Michael T. Jones michael.jo...@gmail.com -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
