Servoy Forum

Same problem, you still have to calculate the VAT and round to whole cents...

You won't believe it, Harjo, but I currently wrote nearly the same:

"Looks very complicated, this matter.
Maybe one solution would be to just store everything in cents instead of Euros, so that one can use only integers."

omar wrote:Same problem, you still have to calculate the VAT and round to whole cents...

True, but you could use integers in JavaScript, too, which have their counterparts as integers in the database.
For calculations you would need a temporary variable that can handle decimals.

However in my feeling that is not very practical in programming, so I overall agree with Harjo.

It's no rocket science, just maths and google on "javascript rounding".

Here our function (we extended the function with the optional parameter _round_part) :

function svy_utl_round(_val, _nr_decs, _round_part) {
if (_val === null) {
return null
}
var _res = _val
if (_val < 0) {
_res = - _val
}
if (_round_part) {
_res = Math.round(_res / _round_part) * _round_part
}
var _pow = _nr_decs ? Math.pow(10, _nr_decs) : 1
_res = _res * _pow
_res = Math.round(_res) / _pow
if (_val < 0) {
_res = - _res
}
return _res
}

lwjwillemsen wrote:It's no rocket science, just maths and google on "javascript rounding".

Here our function (we extended the function with the optional parameter _round_part) :

function svy_utl_round(_val, _nr_decs, _round_part) {
if (_val === null) {
return null
}
var _res = _val
if (_val < 0) {
_res = - _val
}
if (_round_part) {
_res = Math.round(_res / _round_part) * _round_part
}
var _pow = _nr_decs ? Math.pow(10, _nr_decs) : 1
_res = _res * _pow
_res = Math.round(_res) / _pow
if (_val < 0) {
_res = - _res
}
return _res
}

Oke Lambert, it IS rocketscience, did you try to round: 4.725 with your method?? it also returns 4.72

and 4.725 is not the only value what is failing

The fact that JavaScript always treats it as a float is the issue here. Just pass it off to the database as I already posted.

Edit: or perhaps Java can do it better? Plugin idea, anyone ?

ROCLASI wrote:The fact that JavaScript always treats it as a float is the issue here. Just pass it off to the database as I already posted.

Edit: or perhaps Java can do it better? Plugin idea, anyone ?

That's a solution, but how will perfom that, if you use this in a lot calculations?

So far, this method is working for me:

Code: Select all

function core_round_money(vValue) {
   if(vValue<0) {
      return Math.round((vValue - 0.00000001) * 100) / 100;
   } else {
      return Math.round((vValue + 0.00000001) * 100) / 100;
   }
}

I can't find ANY example that fails...

Harjo wrote:That's a solution, but not practical, you can't (or must not) with every calculation or rounding query the database)

Sorry, I fail to follow the logic here.. Not practical? Can't? Must not ?

ROCLASI wrote:Sorry, I fail to follow the logic here.. Not practical? Can't? Must not ?

I have edited my sentence

Oke Lambert, it IS rocketscience, did you try to round: 4.725 with your method?? it also returns 4.72

and 4.725 is not the only value what is failing

Thanks Harjo, did not realize that!
I have added the 0.00000001 addition after the multiplying with 100 in my function.
I believe that is numerical better.

Thanks again for the eye opener!

This works for me:

Code: Select all

function roundPrecision(_nNumber, _nPrecision) {
     _nPrecision = _nPrecision || 0;
     if(_nNumber == null) {
          return null;
     }
   
    var _nMultiplier = Math.pow(10 ,_nPrecision),
          _nRoundedNumber = +( Math.abs(_nNumber) * _nMultiplier ).toFixed( _nPrecision );
    _nRoundedNumber = Math.round( _nRoundedNumber );
   
    return _nRoundedNumber / _nMultiplier * (_nNumber < 0 ? -1 : 1);
}


Alright, I couldn't help myself.
Here is a oneliner based on above code examples:

Code: Select all

/**
* @param {Number} value
* @param {Number} [precision] optional value, default is 0
*/
function round(value, precision) {
    return Math.round( (value + ( (value < 0 ? -1 : 1) * 0.00000001)) * Math.pow(10, (precision||0))) / Math.pow(10, (precision||0));
}

Or the way Marc does it:

Code: Select all

/**
* @param {Number} value
* @param {Number} [precision] optional value, default is 0
*/
function round(value, precision) {
   return Math.round(Number(+ (Math.abs(value) * Math.pow(10, precision || 0)).toFixed(precision || 0))) / Math.pow(10, precision || 0) * (value < 0 ? -1 : 1);
}

And I found another one using the utils.numberFormat (but with a quirk)

Code: Select all

/**
* @param {Number} value
* @param {Number} [precision] optional value, default is 0
*/
function round(value, precision) {
    // ending on 5 doesn't seem to round up, 6 does
    return Number(utils.numberFormat(value + ( (value < 0 ? -1 : 1) * 0.00000000006), "#" + utils.stringLeft(".#############", (precision||0)+1)));
}

They all seem to work correctly with the examples in this thread.


Enjoy


Hope this helps.

Thanks everybody for your contribution!

In my bookcase I found the title "Introduction to numerical computations", James S. Vandergraft.
Nice bed time reading (again)

Servoy could potentially have a round() function
that uses then BigDecimals (and that is what you have to put directly in the record WITHOUT touching it again...

And then the database should be configured as DECIMAL/NUMERIC not float/double

but the problem is then what Harjo already pointed out a bit if you do a lot of calculations in js then all those will be done based on floating point numbers
So this would only be something that rounds "the final" floating point result.

for example if you have a lot of order lines and you display the BTW/VAT per line and everything is calculated and then the total price and the total BTW/VAT is shown.
then what do you do to get the total BTW/VAT?

is that
1> sum all the none rounded values of the lines to a total (or calculate the total price and multiply that that should have the same result)
2> sum all the rounded values

problem with both scenario's that after you round then, that if you then take your calculator that it doesn't add up
with <1> is it is possible that the sum of all the rounded values are bigger or smaller then the total that you show
with <2> that is fixed but then if somebody will really calculate the total price (without vat) * by vat that that doesn't end up (this sound more like a real problem to me, that number should be valid i guess)

So i guess you do <1> and then add a +0.01 or a -.10 somewhere so it really adds up?

Normally I would sum the amounts excluding VAT and calculate the VAT over that. That's how you fill it in in your tax reports which don't allow you to include cents anyway. Discrepancies are unavoidable. But we should distinguish between mathematical rounding issues and financial administration challenges. Mathematical rounding should always be correct in my opinion.

omar wrote:Discrepancies are unavoidable. But we should distinguish between mathematical rounding issues and financial administration challenges. Mathematical rounding should always be correct in my opinion.

Exactly!!