Compute digits of float value before applying factor

When applying the factor, we introduce new rounding issue which falsify the
computation of digits.
So it is better to compute the digits using the initial value (coming from the
string parsing) and update the digits based on the order of the factor.

Closes #13964
(grafted from 3606a9f176d0312d9645d05902b74192391538e4)

--HG--
branch : 6.0

sao/src/common.js

@@ -2085,8 +2085,7 @@
                     return '';
                 }
                 var digit = 0;
-                var factor = Number(field.factor || 1);
-                var string = String(value * factor);
+                var string = String(value);
                 if (string.contains('e')) {
                     var exp = string.split('e')[1];
                     string = string.split('e')[0];
@@ -2095,6 +2094,8 @@
                 if (string.contains('.')) {
                     digit += string.replace(/0+$/, '').split('.')[1].length;
                 }
+                var factor = Number(field.factor || 1);
+                digit -= Math.round(Math.log10(factor));
                 return (value * factor).toFixed(digit);
             };
             var format_selection = function() {

tryton/tryton/common/domain_parser.py

@@ -1,5 +1,6 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
+import math
 from shlex import shlex
 from types import GeneratorType
 import gettext
@@ -334,17 +335,18 @@ def format_value(field, value, target=None, context=None, _quote_empty=False):
                     or isinstance(value, bool))):
             return ''
         digit = 0
-        if isinstance(value, Decimal):
-            cast = Decimal
-        else:
-            cast = float
-        factor = cast(field.get('factor', 1))
-        string_ = str(value * factor)
+        string_ = str(value)
         if 'e' in string_:
             string_, exp = string_.split('e')
             digit -= int(exp)
         if '.' in string_:
             digit += len(string_.rstrip('0').split('.')[1])
+        if isinstance(value, Decimal):
+            cast = Decimal
+        else:
+            cast = float
+        factor = cast(field.get('factor', 1))
+        digit -= round(math.log10(factor))
         return locale.localize(
             '{0:.{1}f}'.format(value * factor or 0, digit), True)