linux-kernel - Re: [PATCH 1/2] lib: Proportions with flexible period

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Date:	Thu, 17 May 2012 23:35:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Wu Fengguang <fengguang.wu@...el.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] lib: Proportions with flexible period

On Tue, 2012-05-15 at 17:43 +0200, Jan Kara wrote:
> +               if (numerator > ((long long)denominator) * max_frac / 100)

Does that even compile on 32bit archs?

Operator precedence is *,/ left-to-right, so that's:

  long long t1 = (long long)denom * max_frac
  long long t2 = t1 / 100;

Which is a 64bit signed division.

There's a reason I used that max_prop_frac thing you removed, it avoids
having to do the division at all and allows a mult and shift instead.


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