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From: George Spelvin <lkml@sdf.org>
To: linux-kernel@vger.kernel.org, lkml@sdf.org, tytso@mit.edu
Cc: Jason@zx2c4.com
Subject: Re: [RFC PATCH v2] random: add get_random_max() function
Date: Thu, 28 Mar 2019 10:00:27 GMT	[thread overview]
Message-ID: <201903281000.x2SA0RcA017002@sdf.org> (raw)
In-Reply-To: <201903270655.x2R6tDjo020894@sdf.org>

By the way, I just noticed that my fallback get_random_max64()
algorithm (if there's no __int128 type) is completely broken and
will need rewriting.

It would work if I rejected and regenerated the high half
if the low half were out of range, but that's not what it does.

The worst case is a range of 0x10000001, where it would return
0x10000000 half the time.

Needs rethinking to find something as simple as possible.
I'm sure I can come up with something, but I'm not averse to
suggestions if anyone has any.

(If I had a reliably fast clz/fls, that would open some
possibilities, but sigh...)

      parent reply	other threads:[~2019-03-28 10:00 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <201903241244.x2OCiL8P011277@sdf.org>
2019-03-24 20:47 ` [RFC PATCH] random: add get_random_max() function Jason A. Donenfeld
2019-03-25  0:28   ` George Spelvin
2019-03-25  1:14   ` George Spelvin
     [not found] ` <201903270655.x2R6tDjo020894@sdf.org>
2019-03-28 10:00   ` George Spelvin [this message]

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