pcu_l1_if: get rid of strange paging group calculation

The PCU uses a 16 bit integer value as paging group which does in fact
not really resamble the paging group. Instead it encodes the last three
digits of the IMSI from which the paging group can be calculated. The
value is then eventually converted back to Ascii-digits and then sent
over the PCU-IF interface. Lets get rid of this weird conversion and
use the IMSI directly.

Change-Id: I40d7fc14c9591b3de091e425faaf325421c70a0e

1 files changed, 10 insertions, 34 deletions

diff --git a/src/pcu_l1_if.cpp b/src/pcu_l1_if.cpp
index 6ec806be..84d39cb7 100644
--- a/src/pcu_l1_if.cpp
+++ b/src/pcu_l1_if.cpp
@@ -59,8 +59,6 @@ extern "C" {
 
 extern void *tall_pcu_ctx;
 
-#define PAGING_GROUP_LEN 3
-
 struct e1_ccu_conn_pars {
 	struct llist_head entry;
 
@@ -78,27 +76,6 @@ struct e1_ccu_conn_pars {
  * when it is needed. */
 static LLIST_HEAD(e1_ccu_table);
 
-/* returns [0,999] on success, > 999 on error */
-uint16_t imsi2paging_group(const char* imsi)
-{
-	uint16_t pgroup = 0;
-	size_t len;
-
-	len = (imsi != NULL) ? strlen(imsi) : 0;
-	if (len < PAGING_GROUP_LEN)
-		return 0xFFFF;
-	imsi += len - PAGING_GROUP_LEN;
-
-	while (*imsi != '\0') {
-		if (!isdigit(*imsi))
-			return 0xFFFF;
-		pgroup *= 10;
-		pgroup += *imsi - '0';
-		imsi++;
-	}
-	return pgroup;
-}
-
 /*
  * PCU messages
  */
@@ -286,24 +263,23 @@ void pcu_l1if_tx_agch(struct gprs_rlcmac_bts *bts, bitvec *block, int plen)
 	pcu_tx_data_req(bts, 0, 0, PCU_IF_SAPI_AGCH, 0, 0, 0, data, sizeof(data));
 }
 
-void pcu_l1if_tx_pch(struct gprs_rlcmac_bts *bts, bitvec *block, int plen, uint16_t pgroup)
+#define IMSI_DIGITS_FOR_PAGING 3
+void pcu_l1if_tx_pch(struct gprs_rlcmac_bts *bts, bitvec *block, int plen, const char *imsi)
 {
-	uint8_t data[PAGING_GROUP_LEN + GSM_MACBLOCK_LEN];
-	int i;
+	uint8_t data[IMSI_DIGITS_FOR_PAGING + GSM_MACBLOCK_LEN];
 
-	/* prepend paging group */
-	for (i = 0; i < PAGING_GROUP_LEN; i++) {
-		data[PAGING_GROUP_LEN - 1 - i] = '0' + (char)(pgroup % 10);
-		pgroup = pgroup / 10;
-	}
-	OSMO_ASSERT(pgroup == 0);
+	/* prepend last three IMSI digits (if present) from which BTS/BSC will calculate the paging group */
+	if (imsi && strlen(imsi) >= IMSI_DIGITS_FOR_PAGING)
+		memcpy(data, imsi + strlen(imsi) - IMSI_DIGITS_FOR_PAGING, IMSI_DIGITS_FOR_PAGING);
+	else
+		memset(data, '0', IMSI_DIGITS_FOR_PAGING);
 
 	/* block provided by upper layer comes without first byte (plen),
 	 * prepend it manually:
 	 */
-	OSMO_ASSERT(sizeof(data) >= PAGING_GROUP_LEN + 1 + block->data_len);
+	OSMO_ASSERT(sizeof(data) >= IMSI_DIGITS_FOR_PAGING + 1 + block->data_len);
 	data[3] = (plen << 2) | 0x01;
-	bitvec_pack(block, data + PAGING_GROUP_LEN + 1);
+	bitvec_pack(block, data + IMSI_DIGITS_FOR_PAGING + 1);
 
 	if (the_pcu->gsmtap_categ_mask & (1 << PCU_GSMTAP_C_DL_PCH))
 		gsmtap_send(the_pcu->gsmtap, 0, 0, GSMTAP_CHANNEL_PCH, 0, 0, 0, 0, data + 3, GSM_MACBLOCK_LEN);