- write32(self.fileobj, self.crc)
+ # The native zlib crc is an unsigned 32-bit integer, but
+ # the Python wrapper implicitly casts that to a signed C
+ # long. So, on a 32-bit box self.crc may "look negative",
+ # while the same crc on a 64-bit box may "look positive".
+ # To avoid irksome warnings from the `struct` module, force
+ # it to look positive on all boxes.
+ write32u(self.fileobj, LOWU32(self.crc))
# self.size may exceed 2GB, or even 4GB