[Form] Improve rounding precision

Author: foaly-nr1

Extension/Core/DataTransformer/NumberToLocalizedStringTransformer.php

@@ -266,7 +266,8 @@ private function round($number)
         if (null !== $this->precision && null !== $this->roundingMode) {
             // shift number to maintain the correct scale during rounding
             $roundingCoef = pow(10, $this->precision);
-            $number *= $roundingCoef;
+            // string representation to avoid rounding errors, similar to bcmul()
+            $number = (string) ($number * $roundingCoef);
 
             switch ($this->roundingMode) {
                 case self::ROUND_CEILING:

Tests/Extension/Core/DataTransformer/NumberToLocalizedStringTransformerTest.php

@@ -307,6 +307,8 @@ public function reverseTransformWithRoundingProvider()
             array(1, '123,44', 123.4, NumberToLocalizedStringTransformer::ROUND_DOWN),
             array(1, '-123,45', -123.4, NumberToLocalizedStringTransformer::ROUND_DOWN),
             array(1, '-123,44', -123.4, NumberToLocalizedStringTransformer::ROUND_DOWN),
+            array(2, '37.37', 37.37, NumberToLocalizedStringTransformer::ROUND_DOWN),
+            array(2, '2.01', 2.01, NumberToLocalizedStringTransformer::ROUND_DOWN),
             // round halves (.5) to the next even number
             array(0, '1234,6', 1235, NumberToLocalizedStringTransformer::ROUND_HALF_EVEN),
             array(0, '1234,5', 1234, NumberToLocalizedStringTransformer::ROUND_HALF_EVEN),