[Click] nsclick rng support for ns3

[Eddie Kohler]

Why not just set the CLICK_RAND_MAX to 0x7FFFFFFFU, which NS can handle 
as well as normal code?

Eddie


On 1/23/13 12:35 PM, Sascha Alexander Jopen wrote:
> Hi Eddie,
>
> I did not implement a fallback method, because i was not sure how to
> handle CLICK_RAND_MAX in case a fall back is necessary. In
> include/click/glue.hh CLICK_RAND_MAX is defined as the maximum value
> supported by the ns3 implementation. However, if we find the simulator
> not supporting random numbers at runtime, falling back to random() or
> rand() could lead to a RAND_MAX, which is different from the defined
> CLICK_RAND_MAX. This could lead to unexpected simulation behaviour. Any
> comments, how to handle this?
>
> Regarding the CLICK_RAND_MAX value itself, i can change the maximum
> value to 0xFFFFFFFFU.
>
> I used 0xFFFFFFFEU in the first place, because, although the ns3
> documentation says, that calling
>
>    uint32_t GetInteger(uint32_t min, uint32_t max)
>
> returns an integer in the range [min,max], this seems not to be true for
> max = 0xFFFFFFFFU. Because this calls internally another method, with
> GetValue(min, max + 1), this results in an overflow. So 0xFFFFFFFEU
> would be the largest possible integer. See around line 187 in file
> src/core/model/random-variable-stream.cc. Either i'm wrong, or this is
> something to report to the ns3 team.
>
> However, i certainly missed the alternative call with a cast of the max
> value 0xFFFFFFFFU to double and back to uint32_t after a call to the
> double based GetValue function. This would lead to a RAND_MAX of
> 0xFFFFFFFFU. I will fix this.
>
> Thanks for reviewing,
> Sascha
>
> On 23.01.2013 16:52, Eddie Kohler wrote:
>> Hey,
>>
>> Two comments.
>> - Breaking random numbers except for nses that export random numbers
>> considered lame. Why not fall back to the normal random number
>> generator?
>> - The RAND_MAX value seems odd. (-2??) Why this value?
>>
>> Eddie
>>
>> On Wed, Jan 23, 2013 at 3:52 AM, Lalith Suresh <suresh.lalith at gmail.com> wrote:
>>> Hi,
>>>
>>> On Mon, Jan 21, 2013 at 12:16 PM, Sascha Alexander Jopen
>>> <jopen at informatik.uni-bonn.de> wrote:
>>>> Hey,
>>>>
>>>> please find attached a patchset for click and ns3 which adds support for
>>>> drawing random numbers within click simulations from the underlying ns3
>>>> random number generator. Each simulated click node has its own uniformly
>>>> distributed random number stream (as opposed to my previously submitted
>>>> patch). This way all nodes have independent random number streams.
>>>>
>>>> Setting the seed or run numbers is done within the simulation by means of
>>>>
>>>> RngSeedManager::SetSeed ();
>>>> RngSeedManager::SetRun ();
>>>>
>>>> or with environment variables or command line parameters.
>>>> See http://www.nsnam.org/docs/manual/html/random-variables.html
>>>>
>>>> I still have no ns2 available. Currently, missing rng support from the
>>>> simulator side is detected and reported but no random numbers are
>>>> available to the simulation. Implementing a fallback method should be
>>>> possible, however. Maybe someone who uses ns2 could provide this?
>>>>
>>>> click-ns3-rng.diff is for the click side and ns3-nsclick-rng.diff for
>>>> the ns3 side.
>>>>
>>>
>>> I had a look through this patch. For clarity, my comment is to rename
>>> the simclick command to SIMCLICK_GET_RANDOM_INT and the
>>> Ipv4ClickRouting method's name to GetRandomVariable(). Otherwise, it
>>> looks good.
>>>
>>> I can push this to ns-3-dev when the click side gets committed.
>>>
>>>> Regards,
>>>> Sascha
>>>>
>>>> --
>>>> Dipl.-Inform. Sascha Jopen
>>>>
>>>> University of Bonn                     Tel.:   +49-228-73-54219
>>>> Institute of Computer Science 4        Fax:    +49-228-73-4571
>>>> Friedrich-Ebert-Allee 144              E-mail: jopen at cs.uni-bonn.de
>>>> D-53113 Bonn, Germany
>>>>
>>>> _______________________________________________
>>>> click mailing list
>>>> click at amsterdam.lcs.mit.edu
>>>> https://amsterdam.lcs.mit.edu/mailman/listinfo/click
>>>>
>>>
>>>
>>>
>>> --
>>> Lalith Suresh
>>> www.lalith.in
>>> _______________________________________________
>>> click mailing list
>>> click at amsterdam.lcs.mit.edu
>>> https://amsterdam.lcs.mit.edu/mailman/listinfo/click
>
>