On Wed, 11 Apr 2007, Shawn O. Pearce wrote: > Olivier Galibert <galibert@xxxxxxxxx> wrote: > > On Wed, Apr 11, 2007 at 08:57:09AM -0400, Nicolas Pitre wrote: > > > Hmmm what we need is a random data generator that always produces the > > > same thing. I'll hack something to replace urandom. > > > > Don't hack something, ues the standard reference, the Mersenne Twister. > > > > http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html > > > > PRNGs are the same as cryptosystems, it's very easy to hack up > > something and get it very, very wrong. And it's unnecessary, since > > there are very good ones available. > > Indeed. Please don't get too excited. We don't want a full fledged random number generator with a period of 2^30000 that is faster than light and impossible to predict, etc, etc. The _only_ thing we want is a convenient way to produce large files with garbage that is neither compressible nor deltifiable, but still reproducible. And for that matter the Mersenne Twister algo is _way_ too heavy for our needs. The one that I just implemented basically boils down to: while (count--) { next = next * 1103515245 + 12345; putchar((next >> 16) & 0xff); } and that does the job perfectly well. Nicolas - To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html