> On Feb 12, 2015, at 9:21 AM, Warren Young <w...@etr-usa.com> wrote: > > d = log2(n^2 / 2p) / 4
In C: double n = num_artifacts; double p = acceptable_probability_of_collision; assert(p < 0.002); int d = ceil(log2((n * n) / (2 * p)) / 4.0); n needs to be a double because squaring 5 and 6 digit numbers gets you into scientific notation territory. We don’t want to require 64-bit ints to get the correct answer, and we need to do FP math with the result anyway. We should use ceil() instead of round() because we need to calculate the smallest number of digits that *exceeds* our requested probability of collision. Going back to my 97,000 hash repository example, we need 14 digits to do that, not 13. _______________________________________________ fossil-users mailing list fossil-users@lists.fossil-scm.org http://lists.fossil-scm.org:8080/cgi-bin/mailman/listinfo/fossil-users
