diff options
Diffstat (limited to 'glucometerutils/drivers/lifescan_common.py')
| -rw-r--r-- | glucometerutils/drivers/lifescan_common.py | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/glucometerutils/drivers/lifescan_common.py b/glucometerutils/drivers/lifescan_common.py index 9a60ab6..f37903a 100644 --- a/glucometerutils/drivers/lifescan_common.py +++ b/glucometerutils/drivers/lifescan_common.py @@ -26,3 +26,27 @@ class InvalidSerialNumber(exceptions.Error): """The serial number is not as expected.""" def __init__(self, serial_number): self.message = 'Serial number %s is invalid.' % serial_number + + +def crc_ccitt(data): + """Calculate the CRC-16-CCITT with LifeScan's common seed. + + Args: + data: (bytes) the data to calculate the checksum of + + Returns: + (int) The 16-bit integer value of the CRC-CCITT calculated. + + This function uses the non-default 0xFFFF seed as used by multiple + LifeScan meters. + """ + crc = 0xffff + + for byte in data: + crc = (crc >> 8) & 0xffff | (crc << 8) & 0xffff + crc ^= byte + crc ^= (crc & 0xff) >> 4 + crc ^= (((crc << 8) & 0xffff) << 4) & 0xffff + crc ^= (crc & 0xff) << 5 + + return (crc & 0xffff) |