> Il giorno 21/mag/2016, alle ore 21:15, Bruce Evans <b...@optusnet.com.au> ha > scritto: > > On Sun, 22 May 2016, Pedro F. Giffuni wrote: > >> Log: >> ndis(4): adjustments for our random() specific implementation. >> >> - Revert r300377: The implementation claims to return a value >> within the range. [1] >> - Adjust the value for the case of a zero seed, whihc according >> to standards should be equivalent to a seed of value 1. > > This was already correct. Standards don't say that a seed of 0 for > srand() means the same as a seed of 1 passed to srand(). They say > that if srand() is not called, then the sequence shall be the same > as if it had been called with a seed of 1. This is already > implemented by using an internal initial value of the seed that is > the result of srand(1). >
OK. I misunderstood the standard. I will revert the if seed thing. (Tomorrow). > The commit gives the following bugs: > - srand() is less random. srand(0) now gives the same sequence as > srand(0) > - srand(0) is not binary compatible. > > My previous mail pointed out the version in libc is the kernel version > with some bugs fixed. It also has some regressions. In the libc > version, srand(seed) sets the internal seed almost directly (it just > adds 1 for technical reasons). The kernel version advances the seed > through 50 iterations of random(). This doesn't really increase > randomness but it makes the linearity relation in the LCG less obvious. > Merging both is out of scope from what I expected to be a much simpler cleanup for ndis(4). I would have liked to replace completely random() with something like Mersenne Twister + unpredictable seed but that is basically a waste of time: developers seem sufficiently happy with random() and when not arc4random() can be used. :-/ Thanks for all this feedback. Pedro. > _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
