Paul M Foster wrote:
> On Mon, Jan 11, 2010 at 04:56:03PM -0500, tedd wrote:
>> The above described rounding algorithm introduces more bias than
>> simply using PHP's round() function, which always rounds down. IMO,
>> modifying rounding is not worth the effort.
>> The "best" rounding algorithm is to look at the last digit and do this:
>> 0 -- no rounding needed.
>> 1-4 round down.
>> 6-9 round up.
>> In the case of 5, then look to the number that precedes it -- if it
>> is even, then round up and if it is odd, then round down -- or vise
>> versa, it doesn't make any difference as long as you are consistent.
>> Here are some examples:
>> 122.4 <-- round down (122)
>> 122.6 <-- round up (123)
>> 122.5 <-- round up (123)
>> 123.4 <-- round down (123)
>> 123.6 <-- round up (124)
>> 123.5 <-- round down (123)
>> There are people who claim that there's no difference, or are at odds
>> with this method, but they simply have not investigated the problem
>> sufficiently to see the bias that rounding up/down causes. However,
>> that difference is very insignificant and can only be seen after tens
>> of thousands iterations. PHP's rounding function is quite sufficient.
> This is called (among other things) "banker's rounding". But PHP's
> round() function won't do banker's rounding, as far as I know.
floor( $val + 0.5 );
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