SI2q: cleanup UARFCN addition

* expand comments, fix typos * constify parameter * move try-add-adjust routine into separate function to facilitate further modifications * remove excessive checks and unnecessary return values * move (UARFCN, Scrambling Code) tuple uniqueness check into separate function and use it early Change-Id: Ia72f848dec40723510ca56868e08081804227d47 Related: OS#2357
2017-09-29 14:10:24 +02:00 · 2017-09-29 14:10:24 +02:00 · 081cebaa6d
parent ff20215db2
commit 081cebaa6d
2 changed files with 90 additions and 88 deletions
--- a/src/libbsc/rest_octets.c
+++ b/src/libbsc/rest_octets.c
@ -232,7 +232,7 @@ static inline int f0_helper(int *sc, size_t length, uint8_t *chan_list)
 }

 /* Estimate how many bits it'll take to append single FDD UARFCN */
-static inline int append_utran_fdd_length(uint16_t u, int *sc, size_t sc_len, size_t length)
+static inline int append_utran_fdd_length(uint16_t u, const int *sc, size_t sc_len, size_t length)
 {
 	uint8_t chan_list[16] = { 0 };
 	int tmp[sc_len], f0;
@ -274,18 +274,42 @@ static inline int append_utran_fdd(struct bitvec *bv, uint16_t u, int *sc, size_
 	return 21 + range1024_p(length);
 }

-/* Append multiple FDD UARFCNs */
-static inline int append_uarfcns(struct bitvec *bv, struct gsm_bts *bts, uint8_t budget)
+static inline int try_adding_uarfcn(struct bitvec *bv, struct gsm_bts *bts, uint16_t uarfcn,
+				    uint8_t num_sc, uint8_t start_pos, uint8_t budget)
 {
-	const uint16_t *u = bts->si_common.data.uarfcn_list, *sc = bts->si_common.data.scramble_list;
-	int i, j, k, rc, st = 0, a[bts->si_common.uarfcn_length];
+	int i, k, rc, a[bts->si_common.uarfcn_length];
+
+	if (budget < 23)
+		return -ENOMEM;
+
+	/* copy corresponding Scrambling Codes: range encoder make in-place modifications */
+	for (i = start_pos, k = 0; i < num_sc; a[k++] = bts->si_common.data.scramble_list[i++]);
+
+	/* estimate bit length requirements */
+	rc = append_utran_fdd_length(uarfcn, a, bts->si_common.uarfcn_length, k);
+	if (rc < 0)
+		return rc; /* range encoder failure */
+
+	if (budget - rc <= 0)
+		return -ENOMEM; /* we have ran out of budget in current SI2q */
+
+	/* compute next offset */
+	bts->u_offset += k;
+
+	return budget - append_utran_fdd(bv, uarfcn, a, k);
+}
+
+/* Append multiple FDD UARFCNs */
+static inline void append_uarfcns(struct bitvec *bv, struct gsm_bts *bts, uint8_t budget)
+{
+	const uint16_t *u = bts->si_common.data.uarfcn_list;
+	int i, rem = budget - 7, st = 0; /* account for constant bits right away */
 	uint16_t cu = u[bts->u_offset]; /* caller ensures that length is positive */
-	uint8_t rem = budget - 7, offset_diff; /* account for constant bits right away */

 	OSMO_ASSERT(budget <= SI2Q_MAX_LEN);

 	if (budget <= 7)
-		return -ENOMEM;
+		return;

 	/* 3G Neighbour Cell Description */
 	bitvec_set_bit(bv, 1);
@ -299,53 +323,24 @@ static inline int append_uarfcns(struct bitvec *bv, struct gsm_bts *bts, uint8_t
 	/* No Bandwidth_FDD */
 	bitvec_set_bit(bv, 0);

-	for (i = bts->u_offset; i < bts->si_common.uarfcn_length; i++) {
-		offset_diff = 0;
-		for (j = st, k = 0; j < i; j++) {
-			a[k++] = sc[j]; /* copy corresponding SCs */
-			offset_diff++; /* compute proper offset step */
-		}
+	for (i = bts->u_offset; i <= bts->si_common.uarfcn_length; i++)
 		if (u[i] != cu) { /* we've reached new UARFCN */
-			rc = append_utran_fdd_length(cu, a, bts->si_common.uarfcn_length, k);
-			if (rc < 0) { /* estimate bit length requirements */
-				return rc;
-			}
+			rem = try_adding_uarfcn(bv, bts, cu, i, st, rem);
+			if (rem < 0)
+				break;

-			if (rem - rc <= 0)
-				break; /* we have ran out of budget in current SI2q */
-			else {
-				rem -= append_utran_fdd(bv, cu, a, k);
-				bts->u_offset += offset_diff;
-			}
-			cu = u[i];
-			st = i; /* update start position */
+			if (i < bts->si_common.uarfcn_length) {
+				cu = u[i];
+				st = i;
+			} else
+				break;
 		}
-	}
-
-	if (rem > 22) {	/* add last UARFCN not covered by previous cycle if it could possibly fit into budget */
-		offset_diff = 0;
-		for (i = st, k = 0; i < bts->si_common.uarfcn_length; i++) {
-			a[k++] = sc[i];
-			offset_diff++;
-		}
-		rc = append_utran_fdd_length(cu, a, bts->si_common.uarfcn_length, k);
-		if (rc < 0) {
-			return rc;
-		}
-
-		if (rem - rc >= 0) {
-			rem -= append_utran_fdd(bv, cu, a, k);
-			bts->u_offset += offset_diff;
-		}
-	}

 	/* stop bit - end of Repeated UTRAN FDD Neighbour Cells */
 	bitvec_set_bit(bv, 0);

 	/* UTRAN TDD Description */
 	bitvec_set_bit(bv, 0);
-
-	return 0;
 }

 /* generate SI2quater rest octets: 3GPP TS 44.018 § 10.5.2.33b */
@ -393,15 +388,9 @@ int rest_octets_si2quater(uint8_t *data, struct gsm_bts *bts)
 	bitvec_set_bit(&bv, 0);

 	rc = SI2Q_MAX_LEN - (bv.cur_bit + 3);
-	if (rc > 0 && bts->si_common.uarfcn_length - bts->u_offset > 0) {
-		rc = append_uarfcns(&bv, bts, rc);
-		if (rc < 0) {
-			LOGP(DRR, LOGL_ERROR, "SI2quater [%u/%u]: failed to append %zu UARFCNs due to range encoding "
-			     "failure: %s\n",
-			     bts->si2q_index, bts->si2q_count, bts->si_common.uarfcn_length, strerror(-rc));
-			return rc;
-		}
-	} else /* No 3G Neighbour Cell Description */
+	if (rc > 0 && bts->si_common.uarfcn_length - bts->u_offset > 0)
+		append_uarfcns(&bv, bts, rc);
+	else /* No 3G Neighbour Cell Description */
 		bitvec_set_bit(&bv, 0);

 	/* No 3G Measurement Parameters Description */
--- a/src/libbsc/system_information.c
+++ b/src/libbsc/system_information.c
@ -182,7 +182,7 @@ uint8_t si2q_num(struct gsm_bts *bts)
 	int rc = make_si2quaters(bts, true);
 	uint8_t num = bts->si2q_index + 1; /* number of SI2quater messages */

-	/* N. B: si2q_num() should NEVER be called during actualSI2q rest octets generation
+	/* N. B: si2q_num() should NEVER be called during actual SI2q rest octets generation
 	   we're not re-entrant because of the following code: */
 	bts->u_offset = 0;
 	bts->e_offset = 0;
@ -239,27 +239,41 @@ int bts_earfcn_add(struct gsm_bts *bts, uint16_t earfcn, uint8_t thresh_hi, uint
 	return r;
 }

+/* Scrambling Code as defined in 3GPP TS 25.213 is 9 bit long so number below is unreacheable upper bound */
+#define SC_BOUND 600
+
+/* Find position for a given UARFCN (take SC into consideration if it's available) in a sorted list
+   N. B: we rely on the assumption that (uarfcn, scramble) tuple is unique in the lists */
+static int uarfcn_sc_pos(const struct gsm_bts *bts, uint16_t uarfcn, uint16_t scramble)
+{
+	const uint16_t *sc = bts->si_common.data.scramble_list;
+	uint16_t i, scramble0 = encode_fdd(scramble, false), scramble1 = encode_fdd(scramble, true);
+	for (i = 0; i < bts->si_common.uarfcn_length; i++)
+		if (uarfcn == bts->si_common.data.uarfcn_list[i]) {
+			if (scramble < SC_BOUND) {
+				if (scramble0 == sc[i] || scramble1 == sc[i])
+					return i;
+			} else
+				return i;
+		}
+
+	return -1;
+}
+
 int bts_uarfcn_del(struct gsm_bts *bts, uint16_t arfcn, uint16_t scramble)
 {
-	uint16_t sc0 = encode_fdd(scramble, false), sc1 = encode_fdd(scramble, true),
-		*ual = bts->si_common.data.uarfcn_list,
-		*scl = bts->si_common.data.scramble_list;
-	size_t len = bts->si_common.uarfcn_length, i;
-	for (i = 0; i < len; i++) {
-		if (arfcn == ual[i] && (sc0 == scl[i] || sc1 == scl[i])) {
-			/* we rely on the assumption that (uarfcn, scramble)
-			   tuple is unique in the lists */
-			if (i != len - 1) { /* move the tail if necessary */
-				memmove(ual + i, ual + i + 1, 2 * (len - i + 1));
-				memmove(scl + i, scl + i + 1, 2 * (len - i + 1));
-			}
-			break;
-		}
-	}
+	uint16_t *ual = bts->si_common.data.uarfcn_list, *scl = bts->si_common.data.scramble_list;
+	size_t len = bts->si_common.uarfcn_length;
+	int pos = uarfcn_sc_pos(bts, arfcn, scramble);

-	if (i == len)
+	if (pos < 0)
 		return -EINVAL;

+	if (pos != len - 1) { /* move the tail if necessary */
+		memmove(ual + pos, ual + pos + 1, 2 * (len - pos + 1));
+		memmove(scl + pos, scl + pos + 1, 2 * (len - pos + 1));
+	}
+
 	bts->si_common.uarfcn_length--;
 	return 0;
 }
@ -267,29 +281,27 @@ int bts_uarfcn_del(struct gsm_bts *bts, uint16_t arfcn, uint16_t scramble)
 int bts_uarfcn_add(struct gsm_bts *bts, uint16_t arfcn, uint16_t scramble, bool diversity)
 {
 	size_t len = bts->si_common.uarfcn_length, i, k = 0;
-	uint16_t scr, chk,
+	uint8_t si2q;
+	int pos = uarfcn_sc_pos(bts, arfcn, scramble);
+	uint16_t scr = diversity ? encode_fdd(scramble, true) : encode_fdd(scramble, false),
 		*ual = bts->si_common.data.uarfcn_list,
-		*scl = bts->si_common.data.scramble_list,
-		scramble1 = encode_fdd(scramble, true),
-		scramble0 = encode_fdd(scramble, false);
-
-	scr = diversity ? scramble1 : scramble0;
-	chk = diversity ? scramble0 : scramble1;
+		*scl = bts->si_common.data.scramble_list;

 	if (len == MAX_EARFCN_LIST)
 		return -ENOMEM;

-	for (i = 0; i < len; i++) /* find the position of arfcn if any */
-		if (arfcn == ual[i])
-			break;
+	if (pos >= 0)
+		return -EADDRINUSE;

-	for (k = 0; i < len; i++) {
-		if (arfcn == ual[i] && (scr == scl[i] || chk == scl[i]))
-			return -EADDRINUSE;
+	/* find the suitable position for arfcn if any */
+	pos = uarfcn_sc_pos(bts, arfcn, SC_BOUND);
+	i = (pos < 0) ? len : pos;
+
+	for (k = 0; i < len; i++)
 		if (scr > scl[i])
 			k = i + 1;
-	}
-	/* we keep lists sorted by scramble code:
+
+	/* we keep lists sorted by scramble code of a given UARFCN:
 	   insert into appropriate position and move the tail */
 	if (len - k) {
 		memmove(ual + k + 1, ual + k, (len - k) * 2);
@ -299,9 +311,10 @@ int bts_uarfcn_add(struct gsm_bts *bts, uint16_t arfcn, uint16_t scramble, bool
 	ual[k] = arfcn;
 	scl[k] = scr;
 	bts->si_common.uarfcn_length++;
+	si2q = si2q_num(bts);

-	if (si2q_num(bts) <= SI2Q_MAX_NUM) {
-		bts->si2q_count = si2q_num(bts) - 1;
+	if (si2q <= SI2Q_MAX_NUM) {
+		bts->si2q_count = si2q - 1;
 		return 0;
 	}