Fix of the rounding error for negative numbers.

Author: codisart

src/Decimal.php

@@ -858,9 +858,12 @@ private static function innerRound($value, $scale = 0)
         $diffDigit = bcsub($value, $rounded, $scale+1);
         $diffDigit = (int)$diffDigit[strlen($diffDigit)-1];
 
-        if ($diffDigit >= 5) {
+        if ($diffDigit >= 5 && $value[0] !== '-') {
             $rounded = bcadd($rounded, bcpow('10', -$scale, $scale), $scale);
         }
+        if ($diffDigit >= 5 && $value[0] === '-') {
+            $rounded = bcsub($rounded, bcpow('10', -$scale, $scale), $scale);
+        }
 
         return $rounded;
     }

tests/Decimal/DecimalRoundTest.php

@@ -23,6 +23,14 @@ public function testRoundWithDecimals()
         $this->assertTrue(Decimal::fromString('3.44')->round(1)->equals(Decimal::fromString('3.4')));
     }
 
+    public function testNegativeRoundWithDecimals()
+    {
+        $this->assertTrue(Decimal::fromString('-5.59059956723478932512')->round(3)->equals(Decimal::fromString('-5.591')));
+        $this->assertTrue(Decimal::fromString('-5.59059956723478932512')->round(4)->equals(Decimal::fromString('-5.5906')));
+        $this->assertTrue(Decimal::fromString('-5.59059956723478932512')->round(5)->equals(Decimal::fromString('-5.59060')));
+        $this->assertTrue(Decimal::fromString('-5.59059956723478932512')->round(6)->equals(Decimal::fromString('-5.590600')));
+    }
+
     public function testNoUsefulRound()
     {
         $this->assertTrue(Decimal::fromString('3.45')->round(2)->equals(Decimal::fromString('3.45')));