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

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Message-ID: <20120518143315.GB6875@quack.suse.cz>
Date:	Fri, 18 May 2012 16:33:15 +0200
From:	Jan Kara <jack@...e.cz>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jan Kara <jack@...e.cz>, 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 Thu 17-05-12 23:35:12, Peter Zijlstra wrote:
> 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.
  Yeah, I misunderstood it's purpose when I read the code originally. I'll
put it back to avoid the division since this is a hot path.

									Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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