[Patches] [Patch #103158] Don't do unsafe arithmetic in xrange object

[noreply@sourceforge.net]

Patch #103158 has been updated. 

Project: python
Category: core (C code)
Status: Open
Submitted by: greg_ball
Assigned to : gvanrossum
Summary: Don't do unsafe arithmetic in xrange object

Follow-Ups:

Date: 2001-Jan-09 06:31
By: greg_ball

Comment:
This is a replacement for patch 103129,
as suggested by tim_one.

Possibly interesting aspects of the patch:

- xrange objects with overflowing lengths are not gratutiously rejected. 
An error is raised only if the length becomes relevant, under len() or
negative indexing.  Bad lengths are stored as -1. Objects with bad lengths
allow any non-negative integer index.

- On 64 bit platforms, sequence multiplication seems to cause an unsafe
cast from long to int.  This patch does not address that issue.

Without my patch, on i686 Linux:
Python 2.0 (#25, Jan  2 2001, 12:18:07)
[GCC 2.95.3 19991030 (prerelease)] on linux2
Type "copyright", "credits" or "license" for more information.
>>> from sys import maxint
>>> x = xrange(maxint) * 2
>>> len(x)
-2
>>> x[-1]
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
SystemError: error return without exception set
>>> y = xrange(maxint/2)*3
>>> len(y)
-1073741827
>>> y[-1]
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
SystemError: error return without exception set                            
   
>>> y.tolist()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
SystemError: listobject.c:33: bad argument to internal function
>>> m = maxint >> 16
>>> xrange(0,maxint,m)
xrange(0, -2147450883, 32767)
>>> (xrange(1)*maxint)*maxint
xrange(1)
>>>  

With my patch
Python 2.0 (#35, Jan  6 2001, 12:54:41)
[GCC 2.95.3 19991030 (prerelease)] on linux2
Type "copyright", "credits" or "license" for more information.             
   
>>> from sys import maxint
>>> x = xrange(maxint) * 2
>>> len(x)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: xrange object too long
>>> x[-1]
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: xrange object too long
>>> y = xrange(maxint/2)*3
>>> len(y)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: xrange object too long
>>> y.tolist()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: xrange object too long
>>> m = maxint >> 16
>>> xrange(0,maxint,m)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: integer addition
>>> (xrange(1)*maxint) * maxint
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: integer multiplication
>>>  

Without patch on Digital Unix
Python 2.0 (#5, Jan  6 2001, 15:42:58) [C] on osf1V4
Type "copyright", "credits" or "license" for more information.
>>> from sys import maxint
>>> m=maxint >> 32
>>> x = xrange(maxint)*2
>>> x
(xrange(9223372036854775807) * 2)
>>> len(x)
-2
>>> x[-1]
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
SystemError: error return without exception set
>>> xrange(0,maxint,m)
xrange(0, -9223372034707292163, 2147483647)
>>> xrange(1)*maxint
xrange(0)
>>> 

With patch
Python 2.0 (#7, Jan  6 2001, 15:52:21) [C] on osf1V4
Type "copyright", "credits" or "license" for more information.
>>> from sys import maxint
>>> m=maxint >> 32
>>> x = xrange(maxint)*2
>>> x
(xrange(9223372036854775807) * 2)
>>> len(x)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: xrange object too long
>>> x[-1]
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: xrange object too long
>>> xrange(0,maxint,m)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OverflowError: integer addition
>>> xrange(1)*maxint
xrange(0)
>>> 

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