[Python-bugs-list] Integer division can crash under Windows (PR#88)

[tim_one@email.msn.com]

Full_Name: Tim Peters
Version: 1.5.2
OS: Win95
Submission from: 1cust9.tnt4.bos1.da.uu.net (63.21.45.9)


i_divmod doesn't catch overflow when dividing
-sys.maxint-1 by -1.  Under Win95, this has two symptoms:

1. Under the debug build, -sys.maxint-1 is returned.

2. Under the release(!) build, Windows kills the
   interpreter with a system division exception.

The difference is due to different division sequences generated by
the compiler (#2 is triggered by the hardware).

The patch below raises OverflowError in this case.

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*** Objects/Old/intobject.c	Fri Mar 19 14:30:38 1999
--- Objects/New/intobject.c	Sun Sep 26 11:55:10 1999
***************
*** 434,441 ****
  		return -1;
  	}
  	if (yi < 0) {
! 		if (xi < 0)
  			xdivy = -xi / -yi;
  		else
  			xdivy = - (xi / -yi);
  	}
--- 434,447 ----
  		return -1;
  	}
  	if (yi < 0) {
! 		if (xi < 0) {
! 			if (yi == -1 && -xi < 0) {
! 				/* most negative / -1 */
! 				err_ovf("integer division");
! 				return -1;
! 			}
  			xdivy = -xi / -yi;
+ 		}
  		else
  			xdivy = - (xi / -yi);
  	}