1 files changed, 51 insertions, 0 deletions
diff --git a/glucometerutils/support/lifescan.py b/glucometerutils/support/lifescan.py
new file mode 100644
index 0000000..1f8234d
--- /dev/null
+++ b/glucometerutils/support/lifescan.py
@@ -0,0 +1,51 @@
+# -*- coding: utf-8 -*-
+"""Common utility functions for LifeScan meters."""
+
+__author__ = 'Diego Elio Pettenò'
+__email__ = 'flameeyes@flameeyes.eu'
+__copyright__ = 'Copyright © 2013, Diego Elio Pettenò'
+__license__ = 'MIT'
+
+from glucometerutils import exceptions
+
+
+class MissingChecksum(exceptions.InvalidResponse):
+  """The response misses the expected 4-digits checksum."""
+  def __init__(self, response):
+    self.message = 'Response is missing checksum: %s' % response
+
+
+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
+
+
+class MalformedCommand(exceptions.InvalidResponse):
+  def __init__(self, message):
+    exceptions.InvalidResponse.__init__(
+      self, 'Malformed command: %s' % message)
+
+
+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)