Patches item #1438991, was opened at 2006-02-26 04:54 Message generated for change (Settings changed) made by mclow 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: Open Resolution: None Priority: 5 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: David Benbennick (dbenbenn) Date: 2006-03-07 13:08 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 ------------------------------------------------------- This SF.Net email is sponsored by xPML, a groundbreaking scripting language that extends applications into web and mobile media. Attend the live webcast and join the prime developer group breaking into this new coding territory! http://sel.as-us.falkag.net/sel?cmd=lnk&kid=110944&bid=241720&dat=121642 _______________________________________________ Boost-bugs mailing list Boost-bugs@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/boost-bugs