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Date:   Mon, 17 Oct 2022 20:39:41 +0000
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From:   "Yann Droneaud" <ydroneaud@opteya.com>
Message-ID: <e50884573b0f88ebd1f5b495476c13f28a5f0aa2@opteya.com>
Subject: Re: [PATCH] random: use rejection sampling for uniform bounded
 random integers
To:     "Eric Biggers" <ebiggers@kernel.org>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
        sneves@dei.uc.pt
In-Reply-To: <Y02ehdiCtHyLErB8@sol.localdomain>
References: <Y02ehdiCtHyLErB8@sol.localdomain>
 <20221017023752.3907-1-Jason@zx2c4.com>
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Hi, 

17 octobre 2022 à 20:27 "Eric Biggers" a écrit:
> On Sun, Oct 16, 2022 at 08:37:53PM -0600, Jason A. Donenfeld wrote:
> 
> > 
> > In order to be efficient, we implement a kernel-specific variant of
> >  Daniel Lemire's algorithm from "Fast Random Integer Generation in an
> >  Interval", linked below. The kernel's variant takes advantage of
> >  constant folding to avoid divisions entirely in the vast majority of
> >  cases, works on both 32-bit and 64-bit architectures, and requests a
> >  minimal amount of bytes from the RNG.
> >  
> >  Link: https://arxiv.org/pdf/1805.10941.pdf
> > 
> 

> Thanks for doing this! Your code looks correct, but it was hard for me to
> understand until I read the paper that is linked to. 

Other algorithms exists that might be easier to understand before the Lemire’s one.
M.E. O’Neil has written a long blog post on many possible alternatives.

https://www.pcg-random.org/posts/bounded-rands.html

Regards.

—- 
Yann Droneaud
OPTEYA