[Bob Ippolito]
> It seems that we should convert the crc32 functions in binascii,
> zlib, etc. to deal with unsigned integers. Currently it seems that 32-
> bit and 64-bit platforms are going to have different results for
> these functions.
binascii.crc32 very deliberately intends to return the same signed
integer values on all platforms. That's what this section at the end
is trying to do:
#if SIZEOF_LONG > 4
/* Extend the sign bit. This is one way to ensure the result is the
* same across platforms. The other way would be to return an
* unbounded unsigned long, but the evidence suggests that lots of
* code outside this treats the result as if it were a signed 4-byte
* integer.
*/
result |= -(result & (1L << 31));
#endif
return PyInt_FromLong(result);
I wouldn't try to fight that, unless that code is buggy (it looks
correct to me). I don't remember "the evidence" now, but Barry & I
found "lots of code" relying on it at the time ;-)
> Should we do the same as the struct module, and do DeprecationWarning
> when the input value is < 0?
If the _result_ is going to change from sometimes-negative to
always-positive, then FutureWarning is most appropriate.
> ...
> None of the unit tests seem to exercise values where 32-bit and 64-
> bit platforms would have differing results, but that's easy enough to
> fix...
As above, it shouldn't be possible to concoct a case where
binascii.crc32's result differ across boxes. That function also
intends to treat negative inputs the same way across boxes.
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