linux-kernel - Re: [PATCH net-next 1/2] random32: add prandom_u32_lt_N and convert "misuses" of reciprocal

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Message-ID: <1389832172.14001.41.camel@joe-AO722>
Date:	Wed, 15 Jan 2014 16:29:32 -0800
From:	Joe Perches <joe@...ches.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jakub Zawadzki <darkjames-ws@...kjames.pl>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH net-next 1/2] random32: add prandom_u32_lt_N and convert
 "misuses" of reciprocal_divide

On Thu, 2014-01-16 at 00:23 +0100, Daniel Borkmann wrote:
> Many functions have open coded a function that return a random
> number in range [0,N-1]. Also, only because we have a function
> that is named reciprocal_divide(), it has not much to do with
> the pupose where it is being used when a previous reciprocal_value()
> has not been obtained.

prandom_u32_lt_N?

I do not like the camelcase name and thought the
prandom_u32_max was better.

How about using

u32 prandom_u32_max(u32 max)
{
	return (u32)(((u64)prandom_u32() * max) >> 32);
}

u32 prandom_u32_range(u32 a, u32 b)
{
	if (b < a)
		swap(a, b);

	return a + (u32)(((u64)prandom_u32() * (b - a)) >> 32);
}


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