lkml.org 
[lkml]   [2008]   [Dec]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe[2]: [PATCH] fork_init: fix division by zero


Hello Scott,

On Wednesday, December 10, 2008 you wrote:

> 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).

Right, such a mask was the result of missed brackets. Now (see
"[PATCH][v2] fork_init: fix division by zero" I've just posted) the
situation is better:

lis r9,0
rlwinm r29,r29,2,0,29
stw r29,0(r9)

I.e. the mask is 0xFFFFFFFC.
Regards, Yuri

--
Yuri Tikhonov, Senior Software Engineer
Emcraft Systems, www.emcraft.com



\
 
 \ /
  Last update: 2008-12-10 18:59    [from the cache]
©2003-2011 Jasper Spaans. Advertise on this site