Fix issues in URBB generation in EGPRS PUAN

Below issue in uncompresed bitmap generation is addressed
1. Corrected the number of bits that is included in URBB
2. If length is not present, 0s are coded as remaining bits
Along with this, code is restructured to enable addition of
compression support

1 files changed, 38 insertions, 35 deletions

diff --git a/src/encoding.cpp b/src/encoding.cpp
index 7d3fa14..dbf0248 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -332,7 +332,7 @@ void Encoding::write_packet_uplink_assignment(
 
 	if (!use_egprs) {
 		bitvec_write_field(dest, wp,0x0,1); // Message escape
-		bitvec_write_field(dest, wp,tbf->current_cs().to_num()-1, 2); // CHANNEL_CODING_COMMAND 
+		bitvec_write_field(dest, wp,tbf->current_cs().to_num()-1, 2); // CHANNEL_CODING_COMMAND
 		bitvec_write_field(dest, wp,0x1,1); // TLLI_BLOCK_CHANNEL_CODING 
 		bitvec_write_field(dest, wp,0x1,1); // switch TIMING_ADVANCE_VALUE = on
 		bitvec_write_field(dest, wp,tbf->ta(),6); // TIMING_ADVANCE_VALUE
@@ -355,7 +355,7 @@ void Encoding::write_packet_uplink_assignment(
 		bitvec_write_field(dest, wp,ws_enc,5); // EGPRS Window Size
 		bitvec_write_field(dest, wp,0x0,1); // No Access Technologies Request
 		bitvec_write_field(dest, wp,0x0,1); // No ARAC RETRANSMISSION REQUEST
-		bitvec_write_field(dest, wp,0x1,1); // TLLI_BLOCK_CHANNEL_CODING 
+		bitvec_write_field(dest, wp,0x1,1); // TLLI_BLOCK_CHANNEL_CODING
 		bitvec_write_field(dest, wp,0x0,1); // No BEP_PERIOD2
 
 		bitvec_write_field(dest, wp,0x1,1); // switch TIMING_ADVANCE_VALUE = on
@@ -612,14 +612,17 @@ static void write_packet_ack_nack_desc_egprs(
 	gprs_rlc_ul_window *window, bool is_final)
 {
 	int urbb_len = 0;
-	int crbb_len = 0;
 	int len;
 	bool bow = true;
 	bool eow = true;
 	int ssn = window->mod_sns(window->v_q() + 1);
 	int num_blocks = window->mod_sns(window->v_r() - window->v_q());
 	int esn_crbb = window->mod_sns(ssn - 1);
-	int rest_bits = dest->data_len * 8 - wp;
+	/* Bit 0 at the end is mandatory Table 11.2.28.1 in 44.060 */
+	int rest_bits = dest->data_len * 8 - wp - 1;
+	int is_compressed = 0;
+	bool len_coded = true;
+	uint8_t i;
 
 	if (num_blocks > 0)
 		/* V(Q) is NACK and omitted -> SSN = V(Q) + 1 */
@@ -627,33 +630,31 @@ static void write_packet_ack_nack_desc_egprs(
 
 	if (num_blocks > window->ws())
 		num_blocks = window->ws();
-
-	if (num_blocks > rest_bits) {
-		eow = false;
-		urbb_len = rest_bits;
-		/* TODO: use compression, start encoding bits and stop when the
-		 * space is exhausted. Use the first combination that encodes
-		 * all bits. If there is none, use the combination that encodes
-		 * the largest number of bits (e.g. by setting num_blocks to the
-		 * max and repeating the construction).
-		 */
-	} else if (num_blocks > rest_bits - 9) {
-		/* union bit and length field take 9 bits */
-		eow = false;
-		urbb_len = rest_bits - 9;
-		/* TODO: use compression (see above) */
-	} else
-		urbb_len = num_blocks;
-
-	if (urbb_len + crbb_len == rest_bits)
-		len = -1;
-	else if (crbb_len == 0)
+	/* TODO Compression support */
+	if (is_compressed == 0) {
+		/* Union bit takes 1 bit */
+		/* Other fields in descr for uncompresed bitmap takes 15 bits*/
+
+		if (num_blocks > rest_bits - 15 - 1) {
+			eow = false;
+			urbb_len = rest_bits - 15 - 1;
+			len_coded = false;
+		} else if (num_blocks == rest_bits - 15 - 1) {
+			urbb_len = rest_bits - 15 - 1;
+			len_coded = false;
+		/* Union bit takes 1 bit length field takes 8 bits*/
+		} else if (num_blocks > rest_bits - 15 - 9) {
+			eow = false;
+			urbb_len = rest_bits - 15 - 9;
+		} else
+			urbb_len = num_blocks;
 		len = urbb_len + 15;
-	else
-		len = urbb_len + crbb_len + 23;
+	} else {
+		/* TODO Compressed bitmap */
+	}
 
 	/* EGPRS Ack/Nack Description IE */
-	if (len < 0) {
+	if (len_coded == false) {
 		bitvec_write_field(dest, wp, 0, 1); // 0: don't have length
 	} else {
 		bitvec_write_field(dest, wp, 1, 1); // 1: have length
@@ -664,17 +665,19 @@ static void write_packet_ack_nack_desc_egprs(
 	bitvec_write_field(dest, wp, bow, 1); // BEGINNING_OF_WINDOW
 	bitvec_write_field(dest, wp, eow, 1); // END_OF_WINDOW
 	bitvec_write_field(dest, wp, ssn, 11); // STARTING_SEQUENCE_NUMBER
-	bitvec_write_field(dest, wp, 0, 1); // 0: don't have CRBB
-
-	/* TODO: Add CRBB support */
-
+	if (is_compressed) {
+		/* TODO Add CRBB support */
+	} else
+		bitvec_write_field(dest, wp, 0, 1); // CRBB_Exist
 	LOGP(DRLCMACUL, LOGL_DEBUG,
-		" - EGPRS URBB, len = %d, SSN = %d, ESN_CRBB = %d, "
+		"EGPRS URBB, urbb len = %d, SSN = %d, ESN_CRBB = %d, "
+		"len present = %s,desc len = %d, "
 		"SNS = %d, WS = %d, V(Q) = %d, V(R) = %d%s%s\n",
-		urbb_len, ssn, esn_crbb,
+		urbb_len, ssn, esn_crbb, len_coded ? "yes" : "No", len,
 		window->sns(), window->ws(), window->v_q(), window->v_r(),
 		bow ? ", BOW" : "", eow ? ", EOW" : "");
-	for (int i = urbb_len; i > 0; i--) {
+
+	for (i = urbb_len; i > 0; i--) {
 		/* Set bit at the appropriate position (see 3GPP TS 04.60 12.3.1) */
 		bool is_ack = window->m_v_n.is_received(esn_crbb + i);
 		bitvec_write_field(dest, wp, is_ack, 1);