Re: [AVTCORE] Review of draft-ietf-avtcore-rfc5764-mux-fixes-02

Marc Petit-Huguenin <petithug@acm.org> Fri, 25 September 2015 10:33 UTC

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To: Paul Kyzivat <pkyzivat@alum.mit.edu>, avt@ietf.org
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From: Marc Petit-Huguenin <petithug@acm.org>
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Date: Fri, 25 Sep 2015 04:33:19 -0600
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Subject: Re: [AVTCORE] Review of draft-ietf-avtcore-rfc5764-mux-fixes-02
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Hi Paul,

On 09/18/2015 10:17 AM, Paul Kyzivat wrote:
> On 9/17/15 4:10 PM, Marc Petit-Huguenin wrote:
> 
>>> K. Section 3:
>>> 
>>> When new values or ranges are added, they MUST be tested in 
>>> ascending order.
>>> 
>> 
>> This text should not talk about adding new values/ranges. Changed
>> the text to:
>> 
>> "The various range values for the first byte MUST be tested in
>> ascending order."
> 
> I just reviewed this, and I have no idea what it means. I see nothing
> about Figure 3 that requires testing to be done in a particular
> order. The *text* suggests an if/then/else or switch statement
> implementation. But the code generated for a switch statement may
> well be a lookup table and so have no particular ordering.
> 
> The only time ordering would matter would be if the ranges
> overlapped. And IIUC the goal here that the ranges *not* overlap.

The reason we added this was to plan when a new overlapping range is added (mostly because someone ignored the advices provided by this draft).  If the algorithm says today that range must be checked in ascending order, then *all* implementations will work (or, most likely, fail) in a similar way.  That sentence is meant to explicitly prevent using a lookup table or perfect hashing or whatever technique that would prevent things to fail identically everywhere.

That said the sentence can probably be improved.

Thanks.

- -- 
Marc Petit-Huguenin
Email: marc@petit-huguenin.org
Blog: http://blog.marc.petit-huguenin.org
Profile: http://www.linkedin.com/in/petithug
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