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-rw-r--r--glucometerutils/drivers/lifescan_common.py38
-rw-r--r--test/test_lifescan.py7
-rw-r--r--test/test_otultra2.py2
3 files changed, 13 insertions, 34 deletions
diff --git a/glucometerutils/drivers/lifescan_common.py b/glucometerutils/drivers/lifescan_common.py
index ac25d22..5b42c33 100644
--- a/glucometerutils/drivers/lifescan_common.py
+++ b/glucometerutils/drivers/lifescan_common.py
@@ -6,8 +6,6 @@ __email__ = 'flameeyes@flameeyes.eu'
__copyright__ = 'Copyright © 2013, Diego Elio Pettenò'
__license__ = 'GPL v3 or later'
-import ctypes
-
from glucometerutils import exceptions
@@ -31,40 +29,20 @@ class InvalidSerialNumber(exceptions.Error):
def calculate_checksum(bytestring):
- """Calculate the "CRC16 Sick" style checksum for LifeScan protocols.
+ """Calculate the checksum used by OneTouch Ultra and Ultra2 devices
Args:
bytestring: the string of which the checksum has to be calculated.
Returns:
- A 16-bit integer that is the checksum for the input.
+ A string with the hexdecimal representation of 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/ .
+ The checksum is a very stupid one: it just sums all the bytes,
+ modulo 16-bit, without any parity.
"""
- 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
+ checksum = 0
- # 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;
+ for byte in bytestring:
+ checksum = (checksum + byte) & 0xffff
- return crcValue
+ return checksum
diff --git a/test/test_lifescan.py b/test/test_lifescan.py
index 774567d..a7446e0 100644
--- a/test/test_lifescan.py
+++ b/test/test_lifescan.py
@@ -20,10 +20,11 @@ from glucometerutils import exceptions
class TestOTUltra2(unittest.TestCase):
def testChecksum(self):
checksum = lifescan_common.calculate_checksum(bytes('T', 'ascii'))
- self.assertEqual(0x5400, checksum)
+ self.assertEqual(0x0054, checksum)
- checksum = lifescan_common.calculate_checksum(bytes('TestString', 'ascii'))
- self.assertEqual(0x0643, checksum)
+ checksum = lifescan_common.calculate_checksum(
+ bytes('T "SAT","08/03/13","22:12:00 "', 'ascii'))
+ self.assertEqual(0x0608, checksum)
if __name__ == '__main__':
unittest.main()
diff --git a/test/test_otultra2.py b/test/test_otultra2.py
index 6ffea83..98fffc8 100644
--- a/test/test_otultra2.py
+++ b/test/test_otultra2.py
@@ -48,7 +48,7 @@ class TestOTUltra2(unittest.TestCase):
def testInvalidSerialNumber(self):
self.mock_readline.return_value = bytes(
- '@ "12345678O" E105\r', 'ascii')
+ '@ "12345678O" 0297\r', 'ascii')
self.assertRaises(lifescan_common.InvalidSerialNumber,
self.device.get_serial_number)