Re: [PATCH] cangen: use long long in time computation for -g to support >2.1s

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 02/07/2013 12:04 PM, Konrad Anton wrote:
> Hello,
> 
> On 07.02.2013 11:41, Marc Kleine-Budde wrote:
>> we're a bit oldschool and discuss the code on the
>> linux-can@vger.kernel.org mailinglist. Feel free to subscribe.
> 
> Can you please put that information on the Gitorious page for the next
> casual committer?
> 
> 
>>>       ts.tv_sec = gap / 1000;
>>> -    ts.tv_nsec = ((int)(gap * 1000000)) % 1000000000;
>>> +    ts.tv_nsec = (long)(((long long)(gap * 1000000)) % 1000000000ll);
>>
>> What's going on here exactly?
>>
>> gap is a double - Will it be converted into an int before multiplication
>> with 1000000? IIRC there is a difference between "gap * 1000000" and
>> "gap * 1000000.0". In the latter the multiplication is done in floating
>> point, because of the ".0".
> 
> gap is a double.
> (gap * 1000000) will cause 1000000 to be converted to intermediate temp1
> of type double,
> temp1 will be truncated to long long temp2, losing its decimals,
> temp2 will be moduloed by 1000000000ll in a long-long mod operation,
> giving temp3.
> temp3 will be truncated to as many bits as long has, and stored in long
> tv_nsec.
> 
> I think it is safe.

Thanks for the details. Looks good. Can I add your Signed-off-by[1] to
the patch?

Marc
[1]
http://lxr.free-electrons.com/source/Documentation/SubmittingPatches#L298
-- 
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