Very small number when totaling

Anon

I have a General Ledger program that goes through and lists transaction for our customers. Basically, it get transactions from the database (data stored in MySql as float(8,2)) lists it and logs the value. While it's going through and listing the transactions, it is also adding the totals together as a balance that it also displays for each listing.

Example:
Id amount balance
101 10 10
102 15 25
103 -20.05 4.95
104 -4.95 0.00

Somtimes, when you do something like subtract 4.95 from 4.95 you will get a very small number like 1.1546319456102E-14. I've tried all types of things to fix this including type casting the variables involved as doubles and formating with sprintf. All that's left is test for this small value and if present, set the 'balance' to zero.

#here is my cluge fix
if ($ledger_balance < .01 && $ledger_balance > -.01) {
$ledger_balance = 0;
}

Anyone got any better ideas how I could deal with this situation?

Thanks,
Chuckc

Anon

Yeh, php's math functions aren't as precise as one would want them to be, take th following php statement.

<?php
$float = 4.95;
echo ($float-($float-0.01));
?>

Now looking at it one would think that the value would be 0.01 but in actual fact php returns this value: 0.0099999999999998

Want to hear the funniest thing, this same function works fine if you subtract any number greater than 0.01 and fails with any number below it, so whats this php is only really accurate to 2 decimal places?

WTF is up with that guys? That kinda precision faults can meen the difference between a good tax return and a bad one. Well I for one will never use php to do any math critical functions with this faulty handling.