[Python-Dev] 32-bit values (was RE: [Python-checkins] python/dist/src/Lib/test test_zlib.py,1.18,1.19)

[Tim Peters]

[Guido]
> Modified Files:
> 	test_zlib.py
> Log Message:
> Portable way of producing unsigned 32-bit hex output to print the
> CRCs.
>
>
> Index: test_zlib.py
> ===================================================================
> RCS file: /cvsroot/python/python/dist/src/Lib/test/test_zlib.py,v
> retrieving revision 1.18
> retrieving revision 1.19
> diff -C2 -d -r1.18 -r1.19
> *** test_zlib.py	23 Jul 2002 19:04:09 -0000	1.18
> --- test_zlib.py	12 Aug 2002 15:26:05 -0000	1.19
> ***************
> *** 13,18 ****
>
>   # test the checksums (hex so the test doesn't break on 64-bit machines)
> ! print hex(zlib.crc32('penguin')), hex(zlib.crc32('penguin', 1))
> ! print hex(zlib.adler32('penguin')), hex(zlib.adler32('penguin', 1))
>
>   # make sure we generate some expected errors
> --- 13,20 ----
>
>   # test the checksums (hex so the test doesn't break on 64-bit machines)
> ! def fix(x):
> !     return "0x%x" % (x & 0xffffffffL)
> ! print fix(zlib.crc32('penguin')), fix(zlib.crc32('penguin', 1))
> ! print fix(zlib.adler32('penguin')), fix(zlib.adler32('penguin', 1))
>
>   # make sure we generate some expected errors

This raises a question:  what should crc32 and adler32 return?  They return
32-bit values, and that's part of external definitions so we can't change
that, but how we *view* "the sign bit" is up to us.  binascii.crc32()
always-- even on 64-bit boxes --returns a value in range(-2**31, 2**31).  I
know that because I forced it to not long ago.  I don't know what the other
guys return (zlib.crc32(), zlib.adler32(), ...?).

It would sure be nice if they returned values in range(0, 2**32) instead.  A
difficulty with changing this stuff is that checksums seem frequently to be
read and written via the struct module, with format code "l", and e.g.

>>> struct.pack("!l", 1L << 31)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: long int too large to convert to int
>>>