implement support for 3-digit MNC with leading zeros

Enable representing three-digit MNC with leading zeros. The MNCs 23 and 023 are
actually different; so far we treated both as 23. Re-encode an incoming BCD or
string of 023 as it were, i.e. not dropping the leading zero as 23.

Break ABI compatibility by changing the size and ordering of structs
gprs_ra_id, osmo_plmn_id, osmo_cell_global_id, ... by adding an mnc_3_digits
flag.

Change ordering in gprs_ra_id because the canonical oder is {Mobile Country
Code, Mobile Network Code}, so have the mcc member first.

ABI compatibility cannot be maintained for struct gprs_ra_id, since it is a
direct member of structs bssgp_bvc_ctx and bssgp_paging_info, and even just
adding a flag to the end would cause ABI changes of those structs. Similarly,
osmo_plmn_id is a direct member of osmo_location_area_id, and so forth.

Add new API to set and read this additional flag to preserve leading zeros:
- osmo_plmn_to_bcd(), osmo_plmn_from_bcd() after
  gsm48_mcc_mnc_to_bcd() and gsm48_mcc_mnc_from_bcd().
- gsm48_decode_lai2(), gsm48_generate_lai2() after
  gsm48_decode_lai(), gsm48_generate_lai().
- gsm0808_create_layer3_2() after gsm0808_create_layer3() and gsm0808_create_layer3_aoip().
- various osmo_*_name() functions in gsm23003.h (osmo_rai_name() still in
  gsm48.h close to struct gprs_ra_id definition). The amount and duplication of
  these may seem a bit overboard, but IMO they do make sense in this way.
  Though most code will soon see patches unifying the data structures used, in
  some cases (vty, ctrl) they are required singled out. Without these
  functions, the formatting ("%0*u", mnc_3_digits ?  3 : 2, mnc) would be
  duplicated all over our diverse repositories.

In various log output, include the leading MNC zeros.

Mark one TODO in card_fs_sim.c, I am not sure how to communicate a leading zero
to/from a SIM card FS. The focus here is on the core network / BSS.

To indicate ABI incompatibility, bump libosmogsm and libosmogb LIBVERSIONs;
adjust debian files accordingly.

Implementation choices:

- The default behavior upon zero-initialization will be the mnc_3_digits flag
  set to false, which yields exactly the previous behavior.

- I decided against packing the mnc with the mnc_3_digits field into a
  sub-struct because it would immediately break all builds of dependent
  projects: it would require immediate merging of numerous patches in other
  repositories, and it would make compiling older code against a newer
  libosmocore unneccessarily hard.

Change-Id: Id2240f7f518494c9df6c8bda52c0d5092f90f221

1 files changed, 129 insertions, 0 deletions

diff --git a/src/gsm/gsm23003.c b/src/gsm/gsm23003.c
index 95ac9f83..63de2b81 100644
--- a/src/gsm/gsm23003.c
+++ b/src/gsm/gsm23003.c
@@ -24,6 +24,7 @@
  */
 
 #include <ctype.h>
+#include <stdio.h>
 
 #include <osmocom/gsm/gsm23003.h>
 #include <osmocom/gsm/protocol/gsm_23_003.h>
@@ -66,3 +67,131 @@ bool osmo_msisdn_str_valid(const char *msisdn)
 {
 	return is_n_digits(msisdn, 1, 15);
 }
+
+/*! Return MCC string as standardized 3-digit with leading zeros.
+ * \param[in] mcc  MCC value.
+ * \returns string in static buffer.
+ */
+const char *osmo_mcc_name(uint16_t mcc)
+{
+	static char buf[8];
+	snprintf(buf, sizeof(buf), "%03u", mcc);
+	return buf;
+}
+
+/*! Return MNC string as standardized 2- or 3-digit with leading zeros.
+ * \param[in] mnc  MNC value.
+ * \param[in] mnc_3_digits  True if an MNC should fill three digits, only has an effect if MNC < 100.
+ * \returns string in static buffer.
+ */
+const char *osmo_mnc_name(uint16_t mnc, bool mnc_3_digits)
+{
+	static char buf[8];
+	snprintf(buf, sizeof(buf), "%0*u", mnc_3_digits ? 3 : 2, mnc);
+	return buf;
+}
+
+static inline void plmn_name(char *buf, size_t buflen, const struct osmo_plmn_id *plmn)
+{
+	snprintf(buf, buflen, "%s-%s", osmo_mcc_name(plmn->mcc),
+		 osmo_mnc_name(plmn->mnc, plmn->mnc_3_digits));
+}
+
+/*! Return MCC-MNC string as standardized 3-digit-dash-2/3-digit with leading zeros.
+ * \param[in] plmn  MCC-MNC value.
+ * \returns string in static buffer.
+ */
+const char *osmo_plmn_name(const struct osmo_plmn_id *plmn)
+{
+	static char buf[16];
+	plmn_name(buf, sizeof(buf), plmn);
+	return buf;
+}
+
+/*! Same as osmo_mcc_mnc_name(), but returning in a different static buffer.
+ * \param[in] plmn  MCC-MNC value.
+ * \returns string in static buffer.
+ */
+const char *osmo_plmn_name2(const struct osmo_plmn_id *plmn)
+{
+	static char buf[16];
+	plmn_name(buf, sizeof(buf), plmn);
+	return buf;
+}
+
+/*! Return MCC-MNC-LAC as string, in a static buffer.
+ * \param[in] lai  LAI to encode, the rac member is ignored.
+ * \returns Static string buffer.
+ */
+const char *osmo_lai_name(const struct osmo_location_area_id *lai)
+{
+	static char buf[32];
+	snprintf(buf, sizeof(buf), "%s-%u", osmo_plmn_name(&lai->plmn), lai->lac);
+	return buf;
+}
+
+static void to_bcd(uint8_t *bcd, uint16_t val)
+{
+	bcd[2] = val % 10;
+	val = val / 10;
+	bcd[1] = val % 10;
+	val = val / 10;
+	bcd[0] = val % 10;
+}
+
+/* Convert MCC + MNC to BCD representation
+ * \param[out] bcd_dst caller-allocated memory for output
+ * \param[in] mcc Mobile Country Code
+ * \param[in] mnc Mobile Network Code
+ * \param[in] mnc_3_digits true if the MNC shall have three digits.
+ *
+ * Convert given mcc and mnc to BCD and write to *bcd_dst, which must be an
+ * allocated buffer of (at least) 3 bytes length. Encode the MNC in three
+ * digits if its integer value is > 99, or if mnc_3_digits is passed true.
+ * Encode an MNC < 100 with mnc_3_digits passed as true as a three-digit MNC
+ * with leading zeros in the BCD representation.
+ */
+void osmo_plmn_to_bcd(uint8_t *bcd_dst, const struct osmo_plmn_id *plmn)
+{
+	uint8_t bcd[3];
+
+	to_bcd(bcd, plmn->mcc);
+	bcd_dst[0] = bcd[0] | (bcd[1] << 4);
+	bcd_dst[1] = bcd[2];
+
+	to_bcd(bcd, plmn->mnc);
+	if (plmn->mnc > 99 || plmn->mnc_3_digits) {
+		bcd_dst[1] |= bcd[2] << 4;
+		bcd_dst[2] = bcd[0] | (bcd[1] << 4);
+	} else {
+		bcd_dst[1] |= 0xf << 4;
+		bcd_dst[2] = bcd[1] | (bcd[2] << 4);
+	}
+}
+
+/* Convert given 3-byte BCD buffer to integers and write results to *mcc and
+ * *mnc. The first three BCD digits result in the MCC and the remaining ones in
+ * the MNC. Return mnc_3_digits as false if the MNC's most significant digit is encoded as 0xF, true
+ * otherwise; i.e. true if MNC > 99 or if it is represented with leading zeros instead of 0xF.
+ * \param[in] bcd_src 	3-byte BCD buffer containing MCC+MNC representations.
+ * \param[out] mcc 	MCC result buffer, or NULL.
+ * \param[out] mnc	MNC result buffer, or NULL.
+ * \param[out] mnc_3_digits	Result buffer for 3-digit flag, or NULL.
+ */
+void osmo_plmn_from_bcd(const uint8_t *bcd_src, struct osmo_plmn_id *plmn)
+{
+	plmn->mcc = (bcd_src[0] & 0x0f) * 100
+		  + (bcd_src[0] >> 4) * 10
+		  + (bcd_src[1] & 0x0f);
+
+	if ((bcd_src[1] & 0xf0) == 0xf0) {
+		plmn->mnc = (bcd_src[2] & 0x0f) * 10
+			  + (bcd_src[2] >> 4);
+		plmn->mnc_3_digits = false;
+	} else {
+		plmn->mnc = (bcd_src[2] & 0x0f) * 100
+			  + (bcd_src[2] >> 4) * 10
+			  + (bcd_src[1] >> 4);
+		plmn->mnc_3_digits = true;
+	}
+}