On Fri, Aug 30, 2013 at 5:28 AM, Eric Blake <ebl...@redhat.com> wrote:
> On 08/30/2013 03:36 AM, Daniel P. Berrange wrote:
> > On Thu, Aug 29, 2013 at 05:19:21PM -0600, Eric Blake wrote:
> >> FreeBSD 10 recently changed their definition of RAND_MAX, to try
> >> and cover the fact that their evenly distributed results really are
> >> a smaller range than a full power of 2. As a result, I did some
> >> investigation, and learned:
> >>
>
> >> +/* The algorithm of virRandomBits relies on gnulib's guarantee that
> >> + * random_r() matches the POSIX requirements on random() of being
> >> + * evenly distributed among exactly [0, 2**31) (that is, we always get
> >> + * exactly 31 bits). While this happens to be the value of RAND_MAX
> >> + * on glibc, note that POSIX only requires RAND_MAX to be tied to the
> >> + * weaker rand(), so there are platforms where RAND_MAX is smaller
> >> + * than the range of random_r(). For the results to be evenly
> >> + * distributed among up to 64 bits, we also rely on the period of
> >> + * random_r() to be at least 2**64, which POSIX only guarantees for
> >> + * random() if you use 256 bytes of state. */
> >> +enum {
> >> + RANDOM_BITS_PER_ITER = 31,
> >> + RANDOM_BITS_MASK = (1U << RANDOM_BITS_PER_ITER) - 1,
> >> +};
> >
> > Using an enum feels a bit wierd for this. Seems like these are
> > simply 2 constants to #define.
>
> Using enums instead of #define makes gdb behave nicer - you can do 'p/x
> RANDOM_BITS_MASK' and actually get a value, instead of having to dig up
> the source file and look for the #define.
>
> >
> > ACK whether you change the enum or not.
>
> Thanks; pushed after tweaking the comment to not trigger a false
> negative during 'make syntax-check'.
>
> --
> Eric Blake eblake redhat com +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
>
>
Thank you, all. Any idea in which release this would be shipped with?
-jgh
--
Jason Helfman | FreeBSD Committer
j...@freebsd.org | http://people.freebsd.org/~jgh | The Power to Serve
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