Date: Sun, 21 Sep 2014 19:56:13 +0400 (MSK) From: Alexander Monakov <amonakov@...ras.ru> To: musl@...ts.openwall.com Subject: Re: [PATCH] fix a bug in the rand48 family of prng On Sun, 21 Sep 2014, Szabolcs Nagy wrote: > * Jens Gustedt <Jens.Gustedt@...ia.fr> [2014-09-21 16:39:34 +0200]: > > > > This fixes a bug found by Nadav Har'El, who observed that musl was giving > > different prn sequences than other systems, even if seeded with the same > > value. > > > > The problem with something like > > > > a = lc | lc<<16 | lc+0ULL<<32; > > > > where lc is an unsigned short and int is 32bit is the following > > > > (1) lc is promoted to int > > (2) the left shift 16 is performed on int > > > > the fix looks ok, but i'm not clear on why it breaks in practice UB on shift shouldn't be a problem here; I think the issue is that "lc | lc<<16" gets sign-extended rather than zero-extended from 32 bit to 64 bit. Alexander
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