gsm23003: add osmo_imei_str_valid()
Verify 14 digit and 15 digit IMEI strings. OsmoHLR will use the 14
digit version to check IMEIs before writing them to the DB.
Place the Luhn checksum code in a dedicated osmo_luhn() function, so
it can be used elsewhere.
Related: OS#2541
Change-Id: Id2d2a3a93b033bafc74c62e15297034bf4aafe61
diff --git a/src/utils.c b/src/utils.c
index 35d70ac..d1da4fa 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -765,4 +765,35 @@
return buf;
}
+/*! Calculate the Luhn checksum (as used for IMEIs).
+ * \param[in] in Input digits in ASCII string representation.
+ * \param[in] in_len Count of digits to use for the input (14 for IMEI).
+ * \returns checksum char (e.g. '3'); negative on error
+ */
+const char osmo_luhn(const char* in, int in_len)
+{
+ int i, sum = 0;
+
+ /* All input must be numbers */
+ for (i = 0; i < in_len; i++) {
+ if (!isdigit(in[i]))
+ return -EINVAL;
+ }
+
+ /* Double every second digit and add it to sum */
+ for (i = in_len - 1; i >= 0; i -= 2) {
+ int dbl = (in[i] - '0') * 2;
+ if (dbl > 9)
+ dbl -= 9;
+ sum += dbl;
+ }
+
+ /* Add other digits to sum */
+ for (i = in_len - 2; i >= 0; i -= 2)
+ sum += in[i] - '0';
+
+ /* Final checksum */
+ return (sum * 9) % 10 + '0';
+}
+
/*! @} */