1 files changed, 70 insertions, 0 deletions
diff --git a/glucometerutils/drivers/lifescan_common.py b/glucometerutils/drivers/lifescan_common.py
new file mode 100644
index 0000000..ac25d22
--- /dev/null
+++ b/glucometerutils/drivers/lifescan_common.py
@@ -0,0 +1,70 @@
+# -*- coding: utf-8 -*-
+"""Common utility functions for LifeScan meters."""
+
+__author__ = 'Diego Elio Pettenò'
+__email__ = 'flameeyes@flameeyes.eu'
+__copyright__ = 'Copyright © 2013, Diego Elio Pettenò'
+__license__ = 'GPL v3 or later'
+
+import ctypes
+
+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 InvalidChecksum(exceptions.InvalidResponse):
+  def __init__(self, expected, gotten):
+    self.message = (
+      'Response checksum not matching: %04x expected, %04x gotten' %
+      (expected, gotten))
+
+
+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 calculate_checksum(bytestring):
+  """Calculate the "CRC16 Sick" style checksum for LifeScan protocols.
+
+  Args:
+    bytestring: the string of which the checksum has to be calculated.
+
+  Returns:
+    A 16-bit integer that is the checksum for the input.
+
+  Credits for this code go to Christian Navalici, who implemented it in his
+  library at https://github.com/cristianav/PyCRC/ .
+  """
+  crcValue = 0x0000
+  prev_c = 0x0000
+
+  for idx, c in enumerate(bytestring):
+    short_c  =  0x00ff & c
+
+    idx_previous = idx - 1
+    short_p  = ( 0x00ff & prev_c) << 8;
+
+    if ( crcValue & 0x8000 ):
+      crcValue = ctypes.c_ushort(crcValue << 1).value ^ 0x8005
+    else:
+      crcValue = ctypes.c_ushort(crcValue << 1).value
+
+    crcValue &= 0xffff
+    crcValue ^= ( short_c | short_p )
+
+    prev_c = short_c
+
+  # After processing, the one's complement of the CRC is calcluated and the
+  # two bytes of the CRC are swapped.
+  low_byte   = (crcValue & 0xff00) >> 8
+  high_byte  = (crcValue & 0x00ff) << 8
+  crcValue   = low_byte | high_byte;
+
+  return crcValue