Hello Al,
On Wednesday, December 10, 2008 you wrote:
> On Wed, Dec 10, 2008 at 01:01:13PM +0300, Yuri Tikhonov wrote:
>> >> + max_threads = mempages * PAGE_SIZE / (8 * THREAD_SIZE);
>> > ^^^^^^^^^^^^^^^^^^^^
>> >> +#endif
>>
>> > Can't this overflow, e.g. on 32-bit machines with HIGHMEM?
>>
>> The multiplier here is not PAGE_SIZE, but [PAGE_SIZE / (8 *
>> THREAD_SIZE)], and this value is expected to be rather small (2, 4, or
>> so).
> 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.
In any case, adding braces as follows probably would be better:
+ max_threads = mempages * (PAGE_SIZE / (8 * THREAD_SIZE));
Right ?
> Only assignment operators (and ?:, in a sense that a ? b : c ? d : e is
> parsed as a ? b : (c ? d : e)) are right-to-left. The rest is left-to-right.
Regards, Yuri
--
Yuri Tikhonov, Senior Software Engineer
Emcraft Systems, www.emcraft.com
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