codec_pref: move match_codec_pref() to separate c-file and add unit-test

At the moment there are three sources that may advertise a list of
supported audio codec/rate settings. There is the MS that advertises
advertises a speech codec list and the MSC that sends a channel type
information element over A and there are also settings in the bsc
configuration file that may restrict the codec/rate types that are
allowed to use.

The function match_codec_pref() looks at all of the three buckets and
selects a codec that satisfies all three. This is already a somewhat
complicated process, overit is very isolated, so lets give it its own
c-file.

Due to the lack of unit-tests it is very hard to make changes here so
lets add also unit-test to make sure that regressions are catched early.

- Put match_codec_pref() and all its helper functions into a separate
  c-file.
- Add a unit test.

Change-Id: Iabedfdcec8b99a319f2d57cbea45c5e36c7b6e29
Related: OS#3361

1 files changed, 6 insertions, 0 deletions

diff --git a/include/osmocom/bsc/codec_pref.h b/include/osmocom/bsc/codec_pref.h
new file mode 100644
index 000000000..6933ceacd
--- /dev/null
+++ b/include/osmocom/bsc/codec_pref.h
@@ -0,0 +1,6 @@
+#pragma once
+
+int match_codec_pref(int *full_rate, enum gsm48_chan_mode *chan_mode,
+		     const struct gsm0808_channel_type *ct,
+		     const struct gsm0808_speech_codec_list *scl,
+		     const struct bsc_msc_data *msc);