Re: Re: qsort fix

I actually think it's legitimate. If your comparison function isn't deterministic, the sorting algorithm may not make sense, and it assumptions one makes when designing a sorting algorithm (at the very least, that there's an order defined on the to-be-sorted set) end up not being valid, and may screw the algorithm. Zeev On Fri, 28 May 1999, Rasmus Lerdorf wrote: > > This is definitely a problem in Solaris's qsort(). The problem is > > that we're really doing something that is kind of non-kosher. > > Everybody else's qsort() seems to handly it fine, though. > > Since qsort() takes a user-supplied comparison function, the > implementation should be robust enough to not crash regardless of what > this comparison function returns. The Solaris man page for qsort just > says: > > The function must return an integer less than, equal to, or > greater than zero to indicate if the first argument is to be > considered less than, equal to, or greater than the second > argument. > > and then under the NOTES: > > The comparison function need not compare every byte, so > arbitrary data may be contained in the elements in addition > to the values being compared. > > The relative order in the output of two items that compare > as equal is unpredictable. > > > So, basically going from the first blurb there, they say, "if the first > argument should be considered less than..." They don't say "if the first > argument *is* less than..." which to me means that it should be valid to > not use the same criteria on every iteration to determine which argument > should be considered less than another. And they definitely don't > explicitly say that the comparison function must always use the same > criteria for comparing two values. > > Silly Sun... > > -Rasmus > > > -- > PHP Development Mailing List http://www.php.net/ > To unsubscribe send an empty message to php-dev-unsubscribe@lists.php.net > For help: php-dev-help@lists.php.net > > -- ----------------------------------------------------- Zeev Suraski <zeev@zend.com> For a PGP public key, finger bourbon@netvision.net.il -- PHP Development Mailing List http://www.php.net/ To unsubscribe send an empty message to php-dev-unsubscribe@lists.php.net For help: php-dev-help@lists.php.net