puzzled, currency display misinterprets exponential notation

[♥bruyndoncx]

In my product bundles the savings are calculated.

For a particular item it showed a wrong number.

I found out it was because of rounding differences there was a difference of -0.00005

echoing the different values during the calculation shows

 

saving: -5.000000000166E-5

 

i did a rudimentory fix by casting to integer and dividing again like this

echo 'saving fix ' . ((int)($bundle_saving*100 ) ) / 100;

 

resulting in the correct result:

saving fix 0

 

the actual display of the savings with the currency notation is generated with this piece of code

    $bundle_saving =  $currencies->display_price($bundle_saving, tep_get_tax_rate($product_info['products_tax_class_id']));

 

so question is, shouldn't the display_price function be able to handle the exponential notation properly ?

or perhaps something wrong with my code ?

 

Can someone try to reproduce this ?

 

I understand i can easily apply this quickfix, but I feel I should fix it for all uses of the currencies->display_price and not just this particular case where I noticed the error.

[MrPhil]

Well... that's a common problem when using "floating point" ("real") numbers in a computer. You often end up with numbers that have a little tail on them when multiplying percentages by percentages. Would you be expecting an answer of 0, or of .00005 as the "correct" answer for $bundle_saving? Maybe a call to tep_round() is needed, to round $bundle_saving to something reasonable (say, nearest .01 Euro or whatever) before the display_price() call to add in the tax calculation.

[Chris H]

Like MrPhil says.

 

It may be worth mentioning that a line such as

 

if ($saving == 0) {

 

can be the source of a puzzling logic error. As for 'tep_round', the osC developers evidently thought it an improvement on php's built-in 'round'. Though I can't see it.