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Date: Sun, 21 Sep 2014 15:57:03 +0200
From: Jens Gustedt <jens.gustedt@...ia.fr>
To: musl@...ts.openwall.com
Cc: Nadav Har'El <nyh@...udius-systems.com>
Subject: Re: Re: drand48() gives wrong sequence?
Am Sonntag, den 21.09.2014, 15:45 +0200 schrieb Jens Gustedt:
> Am Sonntag, den 21.09.2014, 14:27 +0100 schrieb Justin Cormack:
> > Hmm, just checked on a non-OSv Musl system and get the same result as
> > you. I also checked on NetBSD and FreeBSD and they give the same
> > result as glibc, so I think there must be a Musl bug.
>
> In __rand48_step there is this line
>
> x = xi[0] | xi[1]<<16 | xi[2]+0ULL<<32;
>
> on arch with 16bit int this would be UB, no? Do we have such archs,
> still?
Thinking of it, it is UB even on platforms with 32bit if the high
order bit in the unsigned short is set. We then have
unsigned short --> int --> shifted value inside int --> unsigned long
So we better shouldn't do that in any case.
Jens
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