Date: Mon, 17 Feb 2003 08:16:39 +0300 From: "Andrey A. Chernov" <ache@nagual.pp.ru> To: Kris Kennaway <kris@obsecurity.org> Cc: current@FreeBSD.org Subject: Re: cvs commit: src/lib/libc/stdlib rand.c Message-ID: <20030217051639.GA27710@nagual.pp.ru> In-Reply-To: <20030217045729.GA68471@rot13.obsecurity.org> References: <200302170352.h1H3qawJ062671@repoman.freebsd.org> <20030217045729.GA68471@rot13.obsecurity.org>
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[-- Attachment #1 --] On Sun, Feb 16, 2003 at 20:57:29 -0800, Kris Kennaway wrote: > On Sun, Feb 16, 2003 at 07:52:35PM -0800, Andrey A. Chernov wrote: > > > So, monotonically increased seed->first value correlation problem remains... > > I think we should commit this patch (to -current) and fix all the > problems that pop up. For example, it's used in awk (which started > this set of changes), and in some of the XFree86 libraries. I agree. (diff is for old rand.c, but idea is clear in anycase). I have no fancy ideas how to fix correlation problem AND keep rand_r() compatibility at the same time. All linear mod-type generators share this problem with monotonic seeding and usual solution is shuffling array (more complex code than I use), but it will be incompatible with rand_r() again. If we back out most of changes and return to very first formulae with overflow, we 1) Make monotonic increasing for seed->first_value less visible. 2) Not fix seed->first_value correlation (taking some parts of bits will show repeated pattern). 3) Make distribution and lower bits bad. -- Andrey A. Chernov http://ache.pp.ru/ [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.0 (FreeBSD) iQCVAwUBPlBwN+JgpPLZnQjrAQGwBQQApVvTqRAxzggEO1hs1Pdq7d/1680Kl8QQ Wza3gJi6rJv8Duorh0kKBRC4Vi7amL4HMhf85clNBMPTfFTrF1k8hZ4p77Lt/J8T tY9LfRmhEYFfCQPAINbEWxVw33si6FcsaSF+Zdqyt6hZiItmDSKUrAM+nLnAXovy IOB2pdybtD0= =KcEp -----END PGP SIGNATURE-----help
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