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# Validate Percentage Discount with Rounded Values

Posted on 2011-03-03

Hi experts,

Maybe this sounds as a simple question, but a didn't realize eficient way of doing this.

I have a function that needs to validade a discount(%) applied over a product price. Basically, this functions returns false if the discount is greater then the max alowed value.

For example:

Product Price: 10.00

Max Discount: 5%

So, following these parameters, all values greater then 9.50 will be allowed. Other values will not.

Note that until now I didn't applied no kind of rounding.

The problem started when I applied some rounding on calculations.

Suppose that, over a certain price, I discounted 10% and the returned price is 8.87443. If I validate this value on the previous function, the system will check that the discount is 10% and the value will be validated.

But, for some reasons, I need to round this value to 2 decimal places. So, 8.87443 will be changed to 8.87. Submiting this rounded value to the same function will return false becaue the calcutaled discount % will be greater then 10. (10.034, by eg. I didn't calculated the values).

There is some aproaches to apply, like rounding the calculated discount % on the validation function, but, after some tests, I realized that simlple rounding the calculated % will not always work, specially on smaller prices (like 1.00, 0.60 and so on). By eg, a 10.3% of discount on a product that costs 0.78 cents is acceptable, but 10.3% dilscount on a product that costs 10,000.00 are not.

So, I would like to know if anybody has another technique that considers something like rounded decimal places and the original price, that will be able to validate the discount calculated after rounding, if greater than the limit, is acceptable or not.

Thanks a lot for any advice.