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..45f69c3ae8a99f5e288cb2ee202fd24b1d6fe77f 100644
--- a/Source/platform/Decimal.cpp
+++ b/Source/platform/Decimal.cpp
@@ -612,6 +612,21 @@ Decimal::AlignedOperands Decimal::alignOperands(const Decimal& lhs, const Decima
     return alignedOperands;
 }
 
+// Returns true if the 'n' least significant digits of
+// the coefficient are all zero.
+static bool digitsAllZero(uint64_t coefficient, int n)

[yosin_UTC9, 2013/11/18 03:48:28]

How about this?

static bool isMultipleOfTenPowerN(uint64_t coefficient, int n) {
    uint64_t tenPowerN = scaleUp(1, n);
    return !coefficient % tenPowerN;
}

log(N, 2) multiplication + one division may be faster than 2xN division.

[sof, 2013/11/18 06:48:27]

Yes, clearer too. Done + took the opportunity to spot the zero special case.

+{
+    ASSERT(n >= 0);
+    while (n > 0) {
+        if (coefficient % 10) {
+            return false;
+        }
+        coefficient /= 10;
+        n--;

[yosin_UTC9, 2013/11/18 03:48:28]

nit: --n
Other parts of this file use prefix decrement/increment.

+    }
+    return true;
+}
+
 // 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 +643,9 @@ 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() && !digitsAllZero(m_data.coefficient(), numberOfDropDigits))
+        result++;

[yosin_UTC9, 2013/11/18 03:48:28]

nit: ++result
Other parts of this file use prefix decrement/increment.

[sof, 2013/11/18 06:48:27]

Done.

     return Decimal(sign(), 0, result);
 }
 
@@ -670,10 +684,9 @@ 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() && !digitsAllZero(m_data.coefficient(), numberOfDropDigits))
+        result++;

[yosin_UTC9, 2013/11/18 03:48:28]

nit: ++result
Other parts of this file use prefix decrement/increment.

[sof, 2013/11/18 06:48:27]

Done.

     return Decimal(sign(), 0, result);
 }