Replace switch/case construct by a structure, to define coding schemes

A new attribute at TBF instance indicates the current scheme used.
diff --git a/src/gprs_rlcmac.cpp b/src/gprs_rlcmac.cpp
index 64bbe75..e434c4b 100644
--- a/src/gprs_rlcmac.cpp
+++ b/src/gprs_rlcmac.cpp
@@ -71,6 +71,15 @@
 /* N/A */	{ MS_NA,MS_NA,	MS_NA,	MS_NA,	MS_NA,	MS_NA,	MS_NA,	MS_NA },
 };
 
+struct gprs_rlcmac_cs gprs_rlcmac_cs[] = {
+/*	frame length	data block	max payload */
+	{ 0,		0,		0  },
+	{ 23,		23,		20 }, /* CS-1 */
+	{ 34,		33,		30 }, /* CS-2 */
+	{ 40,		39,		36 }, /* CS-3 */
+	{ 54,		53,		50 }, /* CS-4 */
+};
+
 LLIST_HEAD(gprs_rlcmac_ul_tbfs);
 LLIST_HEAD(gprs_rlcmac_dl_tbfs);
 llist_head *gprs_rlcmac_tbfs_lists[] = {
diff --git a/src/gprs_rlcmac.h b/src/gprs_rlcmac.h
index 27cf825..6479754 100644
--- a/src/gprs_rlcmac.h
+++ b/src/gprs_rlcmac.h
@@ -223,6 +223,8 @@
 
 	struct timeval bw_tv; /* timestamp for bandwidth calculation */
 	uint32_t bw_octets; /* number of octets transmitted since bw_tv */
+
+	uint8_t cs; /* current coding scheme */
 };
 
 extern struct llist_head gprs_rlcmac_ul_tbfs; /* list of uplink TBFs */
@@ -249,6 +251,17 @@
 	uint8_t ta;
 };
 
+/*
+ * coding scheme info
+ */
+struct gprs_rlcmac_cs {
+	uint8_t	block_length;
+	uint8_t block_data;
+	uint8_t block_payload;
+};
+
+extern struct gprs_rlcmac_cs gprs_rlcmac_cs[];
+
 int sba_alloc(uint8_t *_trx, uint8_t *_ts, uint32_t *_fn, uint8_t ta);
 
 struct gprs_rlcmac_sba *sba_find(uint8_t trx, uint8_t ts, uint32_t fn);
diff --git a/src/gprs_rlcmac_data.cpp b/src/gprs_rlcmac_data.cpp
index 147054e..2d03ac5 100644
--- a/src/gprs_rlcmac_data.cpp
+++ b/src/gprs_rlcmac_data.cpp
@@ -1289,23 +1289,13 @@
 	/* now we still have untransmitted LLC data, so we fill mac block */
 	index = tbf->dir.dl.v_s & mod_sns_half;
 	data = tbf->rlc_block[index];
-	switch (bts->initial_cs) {
-	case 2: /* CS-2 */
-		block_length = 34;
-		block_data = 33;
-		break;
-	case 3: /* CS-3 */
-		block_length = 40;
-		block_data = 39;
-		break;
-	case 4: /* CS-4 */
-		block_length = 54;
-		block_data = 53;
-		break;
-	default: /* CS-1 */
-		block_length = 23;
-		block_data = 23;
+	if (tbf->cs == 0) {
+		tbf->cs = bts->initial_cs;
+		if (tbf->cs < 1 || tbf->cs > 4)
+			tbf->cs = 1;
 	}
+	block_length = gprs_rlcmac_cs[tbf->cs].block_length;
+	block_data = gprs_rlcmac_cs[tbf->cs].block_data;
 	memset(data, 0x2b, block_data); /* spare bits will be left 0 */
 	rh = (struct rlc_dl_header *)data;
 	rh->pt = 0; /* Data Block */