Edit report at https://bugs.php.net/bug.php?id=61787&edit=1
ID: 61787
Updated by: rasmus@php.net
Reported by: ubuntu at spacetrace dot org
Summary: money_format round error
Status: Not a bug
Type: Bug
Package: Math related
Operating System: Linux ubuntu 11.04
PHP Version: 5.3.10
Block user comment: N
Private report: N
New Comment:
This is getting a bit tiresome. There is no bug here.
Maybe you will understand it this way. Try running this:
<?php
ini_set('precision',32);
$ns = array(1.005, 7.005, 8.005);
foreach($ns as $n) {
echo "$n ".money_format('%.2i', $n)."\n";
}
The output on my machine is:
1.004999999999999893418589635985 1.00
7.004999999999999893418589635985 7.00
8.0050000000000007815970093361102 8.01
That is, 1.005 can't actually be represented accurately and it ends up being
slightly below 1.005 which means when you round it you get 1.00. And 8.005 ends
up being represented as slightly larger than 8.005 so when you round it you get
8.01. It makes perfect sense. Simply add a fuzz factor to your floating point
values to the appropriate precision you care about. Or, as most people know,
when dealing with money, don't use floating point at all. Work in integers.
Previous Comments:
------------------------------------------------------------------------
[2012-04-21 21:55:42] ubuntu at spacetrace dot org
(i meant: money_format('%.2i',8.005) results in 8.01)
------------------------------------------------------------------------
[2012-04-21 21:54:15] ubuntu at spacetrace dot org
money_format('%.2i',1.005) results in 1.00
and
money_format('%.2i',7.005) results in 7.01
this is definitely a bug. you only showed me, the reason, how the bug was created. but it should
still be solved!
Or, if you say, the syntax is not correct, cause you provoke an unpredictable behaviour with
'%.2i' then shouldnt that throw an error notice at least?
why cannot the php-supporters use the same algorythm, like in function round(), where there IS
rounded correctly
------------------------------------------------------------------------
[2012-04-21 21:24:35] rasmus@php.net
Rounding errors compound when you loop like that. There is still no bug here.
------------------------------------------------------------------------
[2012-04-21 21:21:40] ubuntu at spacetrace dot org
now that i uderstand how floating numbers work in computers, this is sure a real bug then:
they say:
"a tiny error in the 17th decimal place doesnât matter at all "
here the bug is at the 3rd place!
and:
" If you just donât want to see all those extra decimal places: simply format your
result rounded to a fixed number of decimal places when displaying it."
this is what i did here and that caused the bug
think about it: NO ONE wants this behaviour if he or she uses '%.2i' in a function
This function should be fixed, so it rounds mathematically correct like the round() function.
If not, then it should throw an error like
"cannot shorten a float variable with this syntax" or so.
------------------------------------------------------------------------
[2012-04-21 18:17:01] rasmus@php.net
How does always rounding down fix anything? What if you are trying to do 3.0 but
you actually get 2.999999999999999, if you always round down you would get 2
instead of 3.
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