Tom,
(inline comments)
On 30-07-13 15:53, Tom Rondeau wrote:
The codec2 needs a bit of attention. I've not known it to fail like
this (and that's a very close result you're seeing), but we need to
update the version of codec2 that we're using. So unless you really
wanted to use codec2 with GNU Radio, just ignore this error since it's
very isolated.
But I must say that there does is quite a difference between the test in
gnuradio 3.6.4.1. and 3.7.0
All the stuff about "data" and "expected data" are simply not present in the
test-script in 3.6.4.1.
Perhaps the thing here is that the script for 3.6.4.1. simply does not do
this "compair with what we expect" test and it might be that this codec2
library is just as wrong on 3.6.4.1 as in 3.7.0
Apparently, in 3.6, we weren't actually properly testing that code.
Some time ago, there was a discussion in the mailing-list about exactly
this, about the effects of code-optimalisation.
It turns out that when you start really optimizing code for specific
processors or specific features (like Single-instruction-multiple-data)
it is very difficult to do so without effecting the outcome of the
codec2 decoding process.
I'm not an expert on ARM code optimalisation but it seams to be that the
way floats are processed will under certain conditions result in very
small differences in the result when you decode a codec2 frame to a PCM
frame.
The difference are very small (after all, you do not hear a difference
of 1 or 2 over a 65536 scale of 16 PCM audio) but they are there!
This was also seen when running the codec2 code on (say) a PPC processor
instead of a intel or a ARM.
Now, I'm not a expert in the low-level code of the codec2 libraries or
on volk, but I think it may be we are seeing the same thing here: that
the code-optimalisation operations in volk result in these small
differences -depending on what processor the code runs on- which is what
causes this particular test to fail in the GNUradio 3.7.0 "make test"
script.
So it might be that it would be better to remove these bit-comparison
tests again as it will probably confuse people. People do expect a "make
test" to result in a 100 % success-rate.
Tom
Chéééééério!
Kr. Bonne.
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