Fix encoding of padding bits to start with 0 bit

This patch is for fixing encoding of padding bits according to the
3gpp spec 44.060 section 11, wherein it shall always start with 0
bit followed with spare padding bits.

During introduction of basic EGPRS feature new hex dump messages
from a different working network log were used in Unit test. These
exposed the issue of incorrect handling of padding bits encoding
in osmo-pcu.

Corrections in the existing test vector of rlcmac is also updated.
In testsuite tbf appropriate corrections for the Tbftest.err is
also done.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/csn1.cpp b/src/csn1.cpp
index 54cc411..82bf17f 100644
--- a/src/csn1.cpp
+++ b/src/csn1.cpp
@@ -2400,7 +2400,12 @@ gint16 csnStreamEncoder(csnStream_t* ar, const CSN_DESCR* pDescr, bitvec *vector
             guint8 bits_to_handle = remaining_bits_len%8;
             if (bits_to_handle > 0)
             {
-              guint8 fl = filler&(0xff>>(8-bits_to_handle));
+              /* section 11 of 44.060
+               * The padding bits may be the 'null' string. Otherwise, the
+               * padding bits starts with bit '0', followed by 'spare padding'
+               * < padding bits > ::= { null | 0 < spare padding > ! < Ignore : 1 bit** = < no string > > } ;
+              */
+              guint8 fl = filler&(0xff>>(8-bits_to_handle + 1));
               bitvec_write_field(vector, writeIndex, fl, bits_to_handle);
               LOGPC(DCSN1, LOGL_NOTICE, "%u|", fl);
               remaining_bits_len -= bits_to_handle;