When picking the end state, looking only at the path metric
is highly suboptimal because in a tail biting code, we _know_ that
whatever treillis path is correct, it must start and end at the same
state. So we only consider path meeting that condition. We know any
path that doesn't isn't the right one. We only fallback to only
path metric if no path met that condition.
Fixes OS#4508
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Change-Id: I87e51d3880c0fe7bf3d6cd08fd46517a424a230c
Remove the paragraph about writing to the Free Software Foundation's
mailing address. The FSF has changed addresses in the past, and may do
so again. In 2021 this is not useful, let's rather have a bit less
boilerplate at the start of source files.
Change-Id: I5050285e75cf120407a1d883e99b3c4bcae8ffd7
Let's fix some erroneous/accidential references to wrong license,
update copyright information where applicable and introduce a
SPDX-License-Identifier to all files.
Change-Id: I39af26c6aaaf5c926966391f6565fc5936be21af
Considering the various styles and implications found in the sources, edit
scores of files to follow the same API doc guidelines around the doxygen
grouping and the \file tag.
Many files now show a short description in the generated API doc that was so
far only available as C comment.
The guidelines and reasoning behind it is documented at
https://osmocom.org/projects/cellular-infrastructure/wiki/Guidelines_for_API_documentation
In some instances, remove file comments and add to the corresponding group
instead, to be shared among several files (e.g. bitvec).
Change-Id: Ifa70e77e90462b5eb2b0457c70fd25275910c72b
Especially for short descriptions, it is annoying to have to type \brief for
every single API doc.
Drop all \brief and enable the AUTOBRIEF feature of doxygen, which always takes
the first sentence of an API doc as the brief description.
Change-Id: I11a8a821b065a128108641a2a63fb5a2b1916e87
It's a pity that even with this patch we still are fare away from having
the whole API documented. However, at least we have a more solid
foundation. Updates not only extend the documentation, but also make
sure it is rendered properly in the doxygen HTML.
Change-Id: I1344bd1a6869fb00de7c1899a8db93bba9bafce3
Add a separate, faster convolution decoding implementation for rates
up to N=4 and constraint lengths of K=5 and K=7, which covers the
most GSM code uses. The decoding algorithm exploits the symmetric
structure of the Viterbi add-compare-select (ACS) operation - commonly
known as the ACS butterfly. This shift-register optimization can be
found in the well-known text by Dave Forney.
Forney, G.D., "The Viterbi Algorithm," Proc. of the IEEE, March 1973.
Implementation is non-architecture specific and improves performance on
x86 as well as ARM processors. Existing API is unchanged with optimized
code being called internally for supported codes.
The original code was relicensed under GPLv2-or-later with permission
of copyright holder - Tom Tsou.
Change-Id: I74d355274b4176a7d924f91ef3c96912ce338fb2
Note that this breaks the ABI and the low level API. But it shouldn't
break the high level API, nor the conv code definitions (because fields
default to 0, and for new fields '0' is the previous behavior)
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
This should have been done with 1dd7c84733
but somehow was missed and only applied to the 'finish' method and
not the 'scan' method.
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
alloca.h is not available on FreeBSD, use the default autoconf
function to check for it, there is a complete list[1] of what to
do for using alloca but let us see how far we get with this test.
Include netinet/in.h for the IPv4 and IPv6 socket address. Check
for dlopen in libraries and use this instead of linking -dl.
[1] http://www.gnu.org/s/hello/manual/autoconf/Particular-Functions.html
If the input value is '0' it should not really affect the error
since it's just an indecisive bit. We accept this either an internal
'0' (generated via puncture) or as an external '0' (generated via an
external puncturing scheme). A real received bit should never be '0',
it's always gonna be closer to 1 or the other value ...
(thanks to mad@auth.se on the ML for the idea)
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Far from perfect but suits our need thus far.
The viterbi with softbit input is quite cpu-intensive. Since
most received bursts are often mostly error free, you could
use a less cpu intensive algorithm (Fano ?) and with hard bit
input. Then only switch to viterbi soft bit input if the channel
is bad enough to justify it.
Soft output is not implemented as its usefulness for the block
coding is limited.
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Harald Welte
Sylvain Munaut
Oliver Smith
Vadim Yanitskiy
Neels Hofmeyr