[Patches] Re: bug in PyLong_FromLongLong (PR#324)

[Trent Mick]

[Thomas]
> there's a bug in PyLong_FromLongLong, resulting in truncation of negative 64 bi
> t
> integers. PyLong_FromLongLong starts with: 
> 	if( ival <= (LONG_LONG)LONG_MAX ) {
> 		return PyLong_FromLong( (long)ival );
> 	}
> 	else if( ival <= (unsigned LONG_LONG)ULONG_MAX ) {
> 		return PyLong_FromUnsignedLong( (unsigned long)ival );
> 	}
> 	else {
>              ....
> 
> Now, if ival is smaller than -LONG_MAX, it falls outside the long integer range
> (being a 64 bit negative integer), but gets handled by the first if-then-case i
> n
> above code ('cause it is, of course, smaller than LONG_MAX). This results in
> truncation of the 64 bit negative integer to a more or less arbitrary 32 bit
> number. The way to fix it is to compare the absolute value of imax against
> LONG_MAX in the first condition. The second condition (ULONG_MAX) must, at
> least, check wether ival is positive. 

On Thu, May 11, 2000 at 09:23:16AM -0400, Guido van Rossum wrote:
> I think he's right.  I have no access to a 64-bit machine -- can you
> come up with a fix and test it?

Yup, Thomas is right. Actually I demonstrated the bug and the fix on linux32
and win32. You need a machine where sizeof(long) != sizeof(LONG_LONG).

Please, see a related email on python-dev about being able to test for this
kind of thing.


Patch Discussion:

Correct bounds checking in PyLong_FromLongLong. Previously, it did not check
properly for negative values when looking checking to see if the given value
fit in a long or unsigned long.


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Patch:


diff -c3  /home/trentm/main/contrib/python/dist/src/Objects/longobject.c ./Objects/longobject.c
*** /home/trentm/main/contrib/python/dist/src/Objects/longobject.c	Wed May  3 16:44:35 2000
--- ./Objects/longobject.c	Thu May 11 14:22:34 2000
***************
*** 355,364 ****
  	/* In case the compiler is faking it. */
  	return PyLong_FromLong( (long)ival );
  #else
! 	if( ival <= (LONG_LONG)LONG_MAX ) {
  		return PyLong_FromLong( (long)ival );
  	}
! 	else if( ival <= (unsigned LONG_LONG)ULONG_MAX ) {
  		return PyLong_FromUnsignedLong( (unsigned long)ival );
  	}
  	else {
--- 355,364 ----
  	/* In case the compiler is faking it. */
  	return PyLong_FromLong( (long)ival );
  #else
! 	if ((LONG_LONG)LONG_MIN <= ival && ival <= (LONG_LONG)LONG_MAX) {
  		return PyLong_FromLong( (long)ival );
  	}
! 	else if (0 <= ival && ival <= (unsigned LONG_LONG)ULONG_MAX) {
  		return PyLong_FromUnsignedLong( (unsigned long)ival );
  	}
  	else {




-- 
Trent Mick
trentm@activestate.com