Unsigned CRC 32 for Python to match Java's CRC 32?

Question

A Python client communicates with a Java server across an unreliable channel, and they must communicate package corruption via CRC32.

On Java's end, the CRC 32 is unsigned:

//where data is a byte[]
crc.update(data, 8, data.length-8);
long chksum = crc.getValue();

But on Python's end, the CRC 32 is signed:

//where some_segment is a bytearray() of data
crc = zlib.crc32(some_segment)

Is there a way to compute the checksum in Python's crc32 to match that of Java's? In other words, make python's crc32 unsigned?

Answer 1

You can bitwise the result with 0xffffffff to get an unsigned value:

crc = zlib.crc32(some_segment) & 0xffffffff

In Python 3 this is the default, so you only need this on python 2.X, but will work for both versions.

Answer 2

Do & 0xffffffff on the crc.