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Diffstat (limited to 'src/utils.c')
| -rw-r--r-- | src/utils.c | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/src/utils.c b/src/utils.c index 35d70ace..d1da4fa8 100644 --- a/src/utils.c +++ b/src/utils.c @@ -765,4 +765,35 @@ const char *osmo_str_toupper(const char *src) 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'; +} + /*! @} */ |