Patches item #1438991, was opened at 2006-02-26 07:54 Message generated for change (Comment added) made by dlwalker You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=307586&aid=1438991&group_id=7586 Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: None Group: None

Status: Closed Resolution: Duplicate Priority: 5 Private: No Submitted By: David Benbennick (dbenbenn) Assigned to: Jonathan Turkanis (turkanis) Summary: rational::operator<(rational) fails due to overflow

Initial Comment: Consider boost::rational<long>. Pick two objects of that type at random (that's well defined, since there are only finitely many objects of that type), and pick them to both have the same sign. Call them a and b. Then the expression "a < b" returns the wrong value 50% of the time! The problem is that the calculation in rational.hpp can overflow, and that overflow actually happens most of the time. Here's a patch that implements operator< without overflow. It's somewhat less efficient (I haven't benchmarked it) but it gives the right answer. Possibly the new version of operator< has bugs. I've run a few hundred million random tests, with the right answer every time (I've used bc to check the answers), but there might be a subtle problem. In particular, the new code assumes that integer division always truncates towards 0, even when dividing negative integers. Perhaps that is not true on some obscure platforms/compilers? ----------------------------------------------------------------------

Comment By: Daryle L. Walker (dlwalker) Date: 2006-11-02 11:28

Message: Logged In: YES user_id=551024 The problem was also described as bug #798357. Your issue should be fixed since I've fixed the other bug. I used continued-fraction expansion, with the components found by the Euclidean GCD algorithm and forcibly floor-rounding division & modulus. ---------------------------------------------------------------------- Comment By: David Benbennick (dbenbenn) Date: 2006-03-07 16:08 Message: Logged In: YES user_id=95581 Here's a new patch that uses std::numeric_limits to select the more efficient, direct comparison method for unbounded types, and only uses the overflow-avoiding method for types that can overflow. ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=307586&aid=1438991&group_id=7586 ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Boost-bugs mailing list Boost-bugs@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/boost-bugs