Posted by tedd on 01/10/06 01:25

>I am calculating things like tax and want to format them so they only have 2
>digits past the decimal point. I've been using sprintf but just noticed that
>it tends to round up. I want the same functionlity without rounding.

Mark:

Rounding?

You can try round(), such as:

<?php
echo round(3.4); // 3
echo round(3.5); // 4
echo round(3.6); // 4
echo round(3.6, 0); // 4
echo round(1.95583, 2); // 1.96
echo round(1241757, -3); // 1242000
echo round(5.045, 2); // 5.05
echo round(5.055, 2); // 5.06
?>

But, as you can see, this rounds up (not the best).

You may want to consider that there is more than one way to round a
number. For example, there is no completely accurate solution for
rounding any real number. If you want absolute precision, then you
must use absolute numbers to whatever precision they are. However,
this may not be obtainable because of continuos numbers like pi. As
such, you may be forced to round.

There are several different algorithms for rounding, such as
truncation, floor (rounding down), ceiling (round up), common, and
statistical. None are perfect, but some are more prone to errors than
others. The least prone to error is the statistical, please review:

"Statisticians method of rounding":

http://en.wikipedia.org/wiki/Rounding

And, if you ignore rounding, please review:

http://www.ima.umn.edu/~arnold/disasters/disasters.html

http://catless.ncl.ac.uk/php/risks/search.php?query=rounding

tedd

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