Re: Math Weirdness

On Tue, 2008-07-15 at 20:17 +0200, Jochem Maas wrote: > Robin Vickery schreef: > > 2008/7/15 tedd <tedd.sperling@gmail.com>: > >> I said: > >> > >> "Round-off errors normally don't enter into things unless your doing > >> multiplication and division operations." > >> > >> And that is not "Bull" -- it's true. You can add and subtract all the > >> floating point numbers (the one's we are talking about here) you want > >> without any rounding errors whatsoever. > > > > $ php -r 'echo 0.7 - 0.2 == 0.5 ? "true\n" : "false\n";' > > false > > > > The operation you do isn't important. You just can't represent certain > > numbers exactly in binary, just as you can't represent 1/3 exactly in > > decimal. They have to be rounded internally. > > which makes php casting so much fun: > > $ php -r 'echo (string)(0.7 - 0.2) == 0.5 ? "true\n" : > "false\n";' > true Just make a simple function... <?php function close_enough( $float1, $float2, $delta=0.000001 ) { return (abs( $float1 - $float2 ) < $delta); } ?> Cheers, Rob. -- http://www.interjinn.com Application and Templating Framework for PHP