note 81824 added to function.round

Many people posting notes here are confused. Do not assume that what you see for a floating point number is the actual value. The value 0.1 can not be represented exactly in binary floating point, no matter how many bits are present in the floating point representation, because 5 does not go into any power of 2. Most other fractions can also not be represented exactly either. For instance, <?php echo 0.285 + 0.0 - 0.285 printf("%.17f", 0.285) - 0.28499999999999998 ?> There is no problem with round(0.285) rounding in the incorrect direction; it is rounding in the correct direction for the argument it is receiving. The problem is that the coder is not being careful with tiny floating point errors that can creep in and become large when things are rounded. For money, one solution is to always store things as an integer, e.g. in cents or mils (thousandths of a monetary unit). Then there is no floating point rounding problem. For other values, where floating point is necessary, I usually add a very small epsilon before rounding, usually about 1e-6 less than the rounding digit. This causes things that look like they should be rounded up, to actually round up. Also, remember to never simply compare a floating point number against another number, even zero, and expect the comparison to work as expected, because of these tiny errors. Always use a small epsilon in the comparison. The direction of the epsilon depends on the intent of the comparison: $a > $b becomes $a > $b + $epsilon, $a >= $b becomes $a >= $b - $epsilon, and $a == $b becomes ($a <= $b + $epsilon && $a >= $b - $epsilon). Please see www.php.net/float ---- Server IP: 208.69.120.35 Probable Submitter: 66.214.49.84 ---- Manual Page -- http://www.php.net/manual/en/function.round.php Edit -- https://master.php.net/note/edit/81824 Del: integrated -- https://master.php.net/note/delete/81824/integrated Del: useless -- https://master.php.net/note/delete/81824/useless Del: bad code -- https://master.php.net/note/delete/81824/bad+code Del: spam -- https://master.php.net/note/delete/81824/spam Del: non-english -- https://master.php.net/note/delete/81824/non-english Del: in docs -- https://master.php.net/note/delete/81824/in+docs Del: other reasons-- https://master.php.net/note/delete/81824 Reject -- https://master.php.net/note/reject/81824 Search -- https://master.php.net/manage/user-notes.php