Fix Decimal.floor() + Decimal.ceiling() for most non-integral values.

Source/platform/Decimal.cpp

Index: Source/platform/Decimal.cpp
diff --git a/Source/platform/Decimal.cpp b/Source/platform/Decimal.cpp
index 02dca8f3691710782a6f9cfc4b41c1d36f4b8272..e1537a793dc63c8a2af91e74ddcd24e5f895de76 100644
--- a/Source/platform/Decimal.cpp
+++ b/Source/platform/Decimal.cpp
@@ -612,6 +612,11 @@ Decimal::AlignedOperands Decimal::alignOperands(const Decimal& lhs, const Decima
     return alignedOperands;
 }
 
+static bool isMultiplePowersOfTen(uint64_t coefficient, int n)
+{
+    return !coefficient || !(coefficient % scaleUp(1, n));
+}
+
 // Round toward positive infinity.
 // Note: Mac ports defines ceil(x) as wtf_ceil(x), so we can't use name "ceil" here.
 Decimal Decimal::ceiling() const
@@ -628,10 +633,9 @@ Decimal Decimal::ceiling() const
     if (numberOfDigits < numberOfDropDigits)
         return isPositive() ? Decimal(1) : zero(Positive);
 
-    result = scaleDown(result, numberOfDropDigits - 1);
-    if (sign() == Positive && result % 10 > 0)
-        result += 10;
-    result /= 10;
+    result = scaleDown(result, numberOfDropDigits);
+    if (isPositive() && !isMultiplePowersOfTen(m_data.coefficient(), numberOfDropDigits))
+        ++result;
     return Decimal(sign(), 0, result);
 }
 
@@ -670,10 +674,9 @@ Decimal Decimal::floor() const
     if (numberOfDigits < numberOfDropDigits)
         return isPositive() ? zero(Positive) : Decimal(-1);
 
-    result = scaleDown(result, numberOfDropDigits - 1);
-    if (isNegative() && result % 10 > 0)
-        result += 10;
-    result /= 10;
+    result = scaleDown(result, numberOfDropDigits);
+    if (isNegative() && !isMultiplePowersOfTen(m_data.coefficient(), numberOfDropDigits))
+        ++result;
     return Decimal(sign(), 0, result);
 }