[Python-Dev] test_gzip/test_tarfile failure om AMD64

[Bob Ippolito]

On May 30, 2006, at 2:41 AM, Nick Coghlan wrote:

> Bob Ippolito wrote:
>> On May 29, 2006, at 8:00 PM, Tim Peters wrote:
>>> We certainly don't want to see two deprecation warnings for a single
>>> deprecated behavior.  I suggest eliminating the "struct integer
>>> wrapping" warning, mostly because I had no idea what it _meant_
>>> before reading the comments in _struct.c  ("wrapping" is used most
>>> often in a proxy or delegation context in Python these days).   "'B'
>>> format requires 0 <= number <= 255" is perfectly clear all by  
>>> itself.
>> What should it be called instead of wrapping? When it says it's   
>> wrapping, it means that it's doing x &= (2 ^ (8 * n)) - 1 to force  
>> a  number into meeting the expected range.
>
> "integer overflow masking" perhaps?

Sounds good enough, I'll go ahead and change the wording to that.

>> Reducing it to one warning instead of two is kinda difficult. Is  
>> it  worth the trouble?
>
> If there are cases where only one warning or the other triggers, it  
> doesn't seem worth the effort to try and suppress one of them when  
> they both trigger.

It works kinda like this:

def get_ulong(x):
	ulong_mask = (sys.maxint << 1L) | 1
	if is_unsigned and ((unsigned)x) > ulong_mask:
		x &= ulong_mask
		warning('integer overflow masking is deprecated')
	return x

def pack_ubyte(x):
	x = get_ulong(x)
	if not (0 <= x <= 255):
		warning("'B' format requires 0 <= number <= 255")
		x &= 0xff
	return chr(x)

Given the implementation, it will warn twice if sizeof(format) <  
sizeof(long) AND one of the following:
1. Negative numbers are given for an unsigned format
2. Input value is greater than ((sys.maxint << 1) | 1) for an  
unsigned format
3. Input value is not ((-sys.maxint - 1) <= x <= sys.maxint) for a  
signed format

-bob