Req #79073 [Opn]: round() does not have PHP_ROUND_UP or PHP_ROUND_DOWN modes

Edit report at https://bugs.php.net/bug.php?id=79073&edit=1 ID: 79073 Updated by: cmb@php.net Reported by: objecttothis at gmail dot com Summary: round() does not have PHP_ROUND_UP or PHP_ROUND_DOWN modes Status: Open Type: Feature/Change Request Package: *Math Functions Operating System: FreeBSD 11.2 PHP Version: 7.4.1 Block user comment: N Private report: N New Comment: The problem is not specificly the rounding, but rather that floating point arithmetic has limited precision[1], so you may have already a wrong result before rounding and rounding does not necessarily fix that. Currency calculations should better be done with BCMath or with integers storing the currency in minor units (e.g. cents). Rounding up is than as simple as adding 1 and truncating (for integers), or adding "0.01" (for BCMath numbers). And if you need division (or multiplication with non-integer values), you may want to use rational numbers for intermediate values. [1] <https://floating-point-gui.de/> Previous Comments: ------------------------------------------------------------------------ [2020-01-07 12:00:32] objecttothis at gmail dot com @cmb I'll bite. What is the best practice for rounding currency if not a floating calculation? Perhaps I'm missing something but if I need to get 51.5 percent of $11.01, the result will be $5.67015. Many times in use the desired rounding would be always up. I really am curious how this should be done without a floating point calculation. ------------------------------------------------------------------------ [2020-01-07 11:39:07] cmb@php.net > When dealing with currency (accounting, discount calculation, > etc) this is often needed. I'd avoid float calculations for currency. ------------------------------------------------------------------------ [2020-01-07 10:55:32] objecttothis at gmail dot com The result, if these modes were added, would be: echo round(1234.231,2,PHP_ROUND_UP); //Output 1234.24 echo round(1234.231,2,PHP_ROUND_DOWN); //Output 1234.23 When dealing with currency (accounting, discount calculation, etc) this is often needed. ------------------------------------------------------------------------ [2020-01-07 10:48:54] objecttothis at gmail dot com Description: ------------ There is no mode in round() that always rounds up or always rounds down. To do this you have to use ceil() or floor() which do not use precision, so the result will always be an integer. If PHP_ROUND_UP and PHP_ROUND_DOWN modes were added, it would resolve this problem. Test script: --------------- <?php function round_up($number, $precision = 2) { $fig = (int) str_pad('1', $precision, '0'); return (ceil($number * $fig) / $fig); } function round_down($number, $precision = 2) { $fig = (int) str_pad('1', $precision, '0'); return (floor($number * $fig) / $fig); } ?> ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=79073&edit=1