[P4-dev] Where should the operations on arbitrary-precision integers be declared?

Javier richardqa at gmail.com
Mon Jun 20 17:37:43 EDT 2016


It works now,

Thank you so much Antonin

regards
Javier

2016-06-20 17:26 GMT-03:00 Javier <richardqa at gmail.com>:

> It is "9a2d5aa38" march 24:(
>
> Please let me try to do it again with the new commit. I write then
>
> Thank you so much
> Javier
>
> 2016-06-20 17:17 GMT-03:00 Antonin Bas <antonin at barefootnetworks.com>:
>
>> What is the latest commit in your behavioral-model clone? Because I added
>> modulo support this morning...
>>
>> On Mon, Jun 20, 2016 at 1:12 PM, Javier <richardqa at gmail.com> wrote:
>>
>>> Hi Antonin,
>>>
>>> Thank you so much for the reply,
>>>
>>> I tried to replicate the code simple_router.p4 with p4v1.1 using the
>>> ideas that you comment: "http://pastebin.com/hukUDq4e"
>>>
>>> As you see, I added one new action "myaction" and one new table "c".
>>>
>>> From command.txt, I just add one entry:
>>>
>>> table_add c myaction 0 => 5 3 0
>>>
>>> Now, in the action ""set_nhop", I changed this line:
>>>
>>> +    ipv4.ttl = ipv4.ttl - 1;
>>> -     ipv4.ttl = ipv4.ttl - routing_metadata.f1;
>>>
>>> Now, I execute run_demo.sh and all ok, but when I do ping between h1 and
>>> h2  I should get this value 62? (64 - 5mod3), However i didn't get to ping
>>> between them (no reply).
>>> If I change the operator '%' to '*' operator It works  64 - 3*5=49 when
>>> ping h1,h2.
>>>
>>> Could you tell me whether am I doing something bad please?
>>>
>>>
>>> Thank you in advance,
>>> Javier
>>>
>>>
>>>
>>>
>>> 2016-06-20 15:39 GMT-03:00 Antonin Bas <antonin at barefootnetworks.com>:
>>>
>>>> Hi,
>>>>
>>>>
>>>> I just noticed that modulo and divide where not supported by the P4
>>>> frontend, so I made the change. In P4v1.1, using modulo would look like
>>>> this:
>>>> action my_action(in int<32> a, in int<32> b) {
>>>>     modify_field(*h1.f1*, a % b);  // a >= 0, b > 0
>>>>     // or *h1.f1* = a % b;
>>>> }
>>>> The second syntax is supported by the p4-hlir compiler, but I don't
>>>> think it is described in the official spec.
>>>> This action can then be referenced by a table.
>>>> Really now that I have made the change in the frontend, using "modulo"
>>>> is no different from using "add" or "substract". See
>>>> https://github.com/p4lang/tutorials/blob/master/p4v1_1/simple_router/p4src/simple_router.p4#L129
>>>> for a P4v1.1 program.
>>>>
>>>> Thanks,
>>>>
>>>> Antonin
>>>>
>>>> On Mon, Jun 20, 2016 at 4:53 AM, Christian Esteve Rothenberg <
>>>> chesteve at dca.fee.unicamp.br> wrote:
>>>>
>>>>> Thanks Antonin for your comprehensive reply!
>>>>>
>>>>> Are you aware of any publicly available P4 code example using the
>>>>> modulo operation?
>>>>>
>>>>> Just a code snippet would suffice...
>>>>>
>>>>> thanks,
>>>>> Christian
>>>>>
>>>>> On Fri, Jun 17, 2016 at 5:05 PM, Antonin Bas
>>>>> <antonin at barefootnetworks.com> wrote:
>>>>> > Hi Javier,
>>>>> >
>>>>> > In P4v1.1, the only variables you have are fields (packet fields and
>>>>> > metadata fields), and they have global scope. These variables all
>>>>> have a
>>>>> > type which includes their bitwidth (with the exception of the very
>>>>> specific
>>>>> > variable-length field case). For example, the ethernet header can be
>>>>> > declared as follows:
>>>>> >
>>>>> > header_type ethernet_t {
>>>>> >     fields {
>>>>> >         bit<48> dstAddr;
>>>>> >         bit<48> srcAddr;
>>>>> >         bit<16> etherType;
>>>>> >     }
>>>>> > }
>>>>> >
>>>>> >
>>>>> > Notice that all three fields are bitstrings. One can also declare
>>>>> fields has
>>>>> > signed integers (int<w>), usually this is more useful for some
>>>>> metadata
>>>>> > fields.
>>>>> > As mentioned in the spec, you cannot declare fields a "int" (without
>>>>> a
>>>>> > width). This is reserved for evaluation of compile-time constants.
>>>>> The "int"
>>>>> > type is used by the compiler but is hidden from the P4 programmer.
>>>>> For
>>>>> > example, let's look at the following code:
>>>>> > ethernet.etherType = (bit<16>) (11111111 - 1);
>>>>> > The compiler will use the internal "int" type to represent
>>>>> compile-time
>>>>> > constants 11111111 and 1. It will also compute the difference,
>>>>> 11111110,
>>>>> > which is also of type "int". This is what we call
>>>>> "arbitrary-precision
>>>>> > arithmetic" since the compiler can handle arbitrarily large compile
>>>>> time
>>>>> > constants. Finally the compiler should give you a warning because
>>>>> 11111110
>>>>> > cannot be represented using 16 bits and the most significant bits
>>>>> will be
>>>>> > lost.
>>>>> >
>>>>> > Best,
>>>>> >
>>>>> > Antonin
>>>>> >
>>>>> >
>>>>> > On Thu, Jun 16, 2016 at 4:13 PM, Javier <richardqa at gmail.com> wrote:
>>>>> >>
>>>>> >> Hi everyone,
>>>>> >>
>>>>> >> I am trying to use the operations on "arbitrary-precison constant
>>>>> >> integers", however I dont get to know how to declare these constant
>>>>> >> integers. In the P4 spec for v1.1 tell that "the only values that
>>>>> can have
>>>>> >> the type int are compile-time constants" but it doesn't show how to
>>>>> use it.
>>>>> >> For example, i want to use the operator modulo to get the modulo of
>>>>> two
>>>>> >> variables, where and how should I declare these variables?.
>>>>> >>
>>>>> >> Thank in advance,
>>>>> >> Javier
>>>>> >>
>>>>> >>
>>>>> >> --
>>>>> >> Saludos Cordiales
>>>>> >> Javier
>>>>> >> Fingerprint: 7AF8 4E03 66C2 2663 3A77  7067 6B5A D8F9 EE91 47BE
>>>>> >>
>>>>> >> _______________________________________________
>>>>> >> P4-dev mailing list
>>>>> >> P4-dev at lists.p4.org
>>>>> >> http://lists.p4.org/mailman/listinfo/p4-dev_lists.p4.org
>>>>> >
>>>>> >
>>>>> >
>>>>> >
>>>>> > --
>>>>> > Antonin
>>>>> >
>>>>> > _______________________________________________
>>>>> > P4-dev mailing list
>>>>> > P4-dev at lists.p4.org
>>>>> > http://lists.p4.org/mailman/listinfo/p4-dev_lists.p4.org
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Antonin
>>>>
>>>
>>>
>>>
>>> --
>>> Saludos Cordiales
>>> Javier
>>> PhD Student (UNICAMP)
>>> http://www.linkedin.com/in/richardqa
>>> Fingerprint: 7AF8 4E03 66C2 2663 3A77  7067 6B5A D8F9 EE91 47BE
>>>
>>
>>
>>
>> --
>> Antonin
>>
>
>
>
> --
> Saludos Cordiales
> Javier
> PhD Student (UNICAMP)
> http://www.linkedin.com/in/richardqa
> Fingerprint: 7AF8 4E03 66C2 2663 3A77  7067 6B5A D8F9 EE91 47BE
>



-- 
Saludos Cordiales
Javier
PhD Student (UNICAMP)
http://www.linkedin.com/in/richardqa
Fingerprint: 7AF8 4E03 66C2 2663 3A77  7067 6B5A D8F9 EE91 47BE
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.p4.org/pipermail/p4-dev_lists.p4.org/attachments/20160620/01c84ee3/attachment-0002.html>


More information about the P4-dev mailing list