Date: Wed, 10 Dec 2008 11:25:12 -0600
From: Scott Wood <scottwood@freescale.com>
To: Yuri Tikhonov <yur@emcraft.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>, Wolfgang Denk <wd@denx.de>,
       Detlev Zundel <dzu@denx.de>, linux-kernel@vger.kernel.org,
       Milton Miller <miltonm@bga.com>, linuxppc-dev@ozlabs.org,
       Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>,
       Ilya Yanok <yanok@emcraft.com>
Subject: Re: [PATCH] fork_init: fix division by zero
Message-ID: <20081210172512.GA19584@ld0162-tx32.am.freescale.net>
References: <200812092044.40649.yur@emcraft.com> <Pine.LNX.4.64.0812100944080.25126@vixen.sonytel.be> <503391615.20081210130113@emcraft.com> <20081210101745.GG28946@ZenIV.linux.org.uk> <1795455197.20081210132912@emcraft.com>
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On Wed, Dec 10, 2008 at 01:29:12PM +0300, Yuri Tikhonov wrote:
> On Wednesday, December 10, 2008 you wrote:
> > x * y / z is parsed as (x * y) / z, not x * (y / z).
> 
>  Here we believe in preprocessor: since all PAGE_SIZE, 8, and 
> THREAD_SIZE are the constants we expect it will calculate this.
> 
>  E.g. here is the result from this line as produced by cross-gcc 
> 4.2.2:
> 
>         lis     r9,0
>         rlwinm  r29,r29,2,16,29
>         stw     r29,0(r9)
> 
>  As you see - only rotate-left, i.e. multiplication to the constant.

Yes, and also note that it is masking the result by 0xfffc, to preserve
the effect of any overflow in (x * y).

-Scott
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