[FIX] web: Python-like rounding method

Javascript and Python handle the rounding of -x.5 differently.

In JS, `Math.round(-0.5)` is equal to `-0`.
In Python, `round(-0.5)` is equal to `-1`.

This will lead to inconsistencies between Python and Javascript, but it
can also lead to inconsistencies in the Javascript itself. Indeed, in
the POS, a refund to the client is entered as a negative number. For
example, `4.245` will be rounded to `4.25`, but a refund of `-4.245`
will be rounded to `-4.24`. The payment and the refund are not
consistent.

Sources:
- http://www.ecma-international.org/ecma-262/6.0/index.html#sec-math.round
- https://docs.python.org/2/library/functions.html#round
- https://en.wikipedia.org/wiki/Rounding#Round_half_up

Fixes #9249
opw-653034
This commit is contained in:
Nicolas Martinelli 2015-11-03 17:11:45 +01:00
parent 2f35c40714
commit ea2c80cad0
1 changed files with 10 additions and 1 deletions

View File

@ -350,7 +350,16 @@ instance.web.round_precision = function(value, precision){
var epsilon_magnitude = Math.log(Math.abs(normalized_value))/Math.log(2);
var epsilon = Math.pow(2, epsilon_magnitude - 53);
normalized_value += normalized_value >= 0 ? epsilon : -epsilon;
var rounded_value = Math.round(normalized_value);
/**
* Javascript performs strictly the round half up method, which is asymmetric. However, in
* Python, the method is symmetric. For example:
* - In JS, Math.round(-0.5) is equal to -0.
* - In Python, round(-0.5) is equal to -1.
* We want to keep the Python behavior for consistency.
*/
var sign = normalized_value < 0 ? -1.0 : 1.0;
var rounded_value = sign * Math.round(Math.abs(normalized_value));
return rounded_value * precision;
};