librmn no longer has crc32 method

[neishm]

See: https://github.com/armnlib/librmn/commit/686e512be455beec14426592a8bbc5f58b551286

If Python-RPN is used with librmn 016.3, it immediately fails with an AttributeError from ctypes, due to a missing crc32 symbol.

[jeixav]

I asked @djamelghb about this. It looks like librmn's crc32 duplicates zlib's. Could Python-RPN switch to using the crc32 function in the standard library (https://docs.python.org/library/zlib.html#zlib.crc32)?

[neishm]

I just ran a simple test to compare the two methods, and it looks like yes, it can be switched to zlib. Test code:

import rpnpy.librmn.all as rmn
import zlib
import numpy as np
for i in range(10):
  buf = np.random.randint(1<<32,size=1000,dtype='uint32')
  crc0 = np.random.randint(1<<32,dtype='uint32')
  from_rmn = rmn.crc32(crc0,buf)
  from_zlib = zlib.crc32(buf,crc0) & 0xffffffff
  print "%08x %08x %s"%(from_rmn, from_zlib, from_rmn == from_zlib)

Result:

776a3602 776a3602 True
87c57921 87c57921 True
3211a345 3211a345 True
4be42d64 4be42d64 True
ee23d303 ee23d303 True
6a9fa480 6a9fa480 True
b484f849 b484f849 True
099663b5 099663b5 True
f0e5d259 f0e5d259 True
7b92fbae 7b92fbae True

I had to apply the 0xffffffff as mentioned in the Python documentation (linked by @jeixav), otherwise it returns a signed integer.

[meteokid]

merged into rpnpy_2.1-branch