[gsm48] Introduce a gsm48_generate_mid_from_imsi method
Prefix generate_mid_from_tmsi with a gsm48_, create a new method
to binary encode the imsi. Add a unit test for parsing and decoding.
The implementation can parse the data it generated and the
last octet seems to be filled with the end mark.
diff --git a/openbsc/src/gsm_04_08_utils.c b/openbsc/src/gsm_04_08_utils.c
index e771ea3..c62f04d 100644
--- a/openbsc/src/gsm_04_08_utils.c
+++ b/openbsc/src/gsm_04_08_utils.c
@@ -164,6 +164,12 @@
return 'A' + (bcd - 0xa);
}
+/* only works for numbers in ascci */
+static u_int8_t char2bcd(char c)
+{
+ return c - 0x30;
+}
+
void gsm0408_generate_lai(struct gsm48_loc_area_id *lai48, u_int16_t mcc,
u_int16_t mnc, u_int16_t lac)
@@ -187,7 +193,7 @@
lai48->lac = htons(lac);
}
-int generate_mid_from_tmsi(u_int8_t *buf, u_int32_t tmsi)
+int gsm48_generate_mid_from_tmsi(u_int8_t *buf, u_int32_t tmsi)
{
u_int32_t *tptr = (u_int32_t *) &buf[3];
@@ -199,6 +205,35 @@
return 7;
}
+int gsm48_generate_mid_from_imsi(u_int8_t *buf, const char *imsi)
+{
+ unsigned int length = strlen(imsi), i, off = 0;
+ u_int8_t odd = (length & 0x1) == 1;
+
+ buf[0] = GSM48_IE_MOBILE_ID;
+ buf[2] = char2bcd(imsi[0]) << 4 | GSM_MI_TYPE_IMSI | (odd << 3);
+
+ /* if the length is even we will fill half of the last octet */
+ if (odd)
+ buf[1] = (length + 1) >> 1;
+ else
+ buf[1] = (length + 2) >> 1;
+
+ for (i = 1; i < buf[1]; ++i) {
+ u_int8_t lower, upper;
+
+ lower = char2bcd(imsi[++off]);
+ if (!odd && off + 1 == length)
+ upper = 0x0f;
+ else
+ upper = char2bcd(imsi[++off]) & 0x0f;
+
+ buf[2 + i] = (upper << 4) | lower;
+ }
+
+ return 2 + buf[1];
+}
+
/* Section 9.1.8 / Table 9.9 */
struct chreq {
u_int8_t val;