Re: [Discuss-gnuradio] new to GNUradio: AFSK and codec2 gmsk modem

[Tom Rondeau]

On Tue, Jul 30, 2013 at 4:47 PM, Kristoff Bonne <address@hidden> wrote:
> Marcus,
>
> (repost due to technical problems. My appolologies for a possible double
> post).
>
>
>
> On 30-07-13 21:41, Marcus D. Leech wrote:
>>
>> On 07/30/2013 03:35 PM, Kristoff Bonne wrote:
>>>
>>> Tom,
>>>
>>>
>>> (inline comments)
>>>
>>>
>> My understanding was that all IEEE floating-point implementations followed
>> the same rounding rules, etc?  Is that not the case?
>>
>> Are the SIMD subsystems not IEEE compliant, for performance reasons?

Yeah, actually, not all SIMD subsytems are IEEE compliant, though off
the top of my head, I can't tell you any more than that. So it is
possible that precision issues can come into play here. There are a
number of Issues on our project page that I believe are related to
this exact problem (basically on different ARM processors with and
without NEON).


> As said, I'm not an expert in code-optimisation.
>
> I did look up the discussions. It was more then "a few weeks ago", they date
> back to January this year. :-)
>
> There are two discussions that might be interesting:
> http://sourceforge.net/mailarchive/forum.php?forum_name=freetel-codec2&viewmonth=201301
>
> "c2dec produces different wav-files on i386 and on ARM" and "adding compiler
> flags"

So codec2 shouldn't be using Volk, but if it's using some other SIMD
code itself, that could be a problem.

The problem with just turning off a QA test because it fails is that
we're now just hiding a potential problem. I'd rather understand the
problem and try and patch it as opposed to shutting our eyes and
pretending everything's ok :)

-- 
Tom
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