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

Source/platform/Decimal.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 594 matching lines @@
         }
     }
 
     AlignedOperands alignedOperands;
     alignedOperands.exponent = exponent;
     alignedOperands.lhsCoefficient = lhsCoefficient;
     alignedOperands.rhsCoefficient = rhsCoefficient;
     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
 {
     if (isSpecial())
         return *this;
 
     if (exponent() >= 0)
         return *this;
 
     uint64_t result = m_data.coefficient();
     const int numberOfDigits = countDigits(result);
     const int numberOfDropDigits = -exponent();
     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);
 }
 
 Decimal Decimal::compareTo(const Decimal& rhs) const
 {
     const Decimal result(*this - rhs);
     switch (result.m_data.formatClass()) {
     case EncodedData::ClassInfinity:
         return result.isNegative() ? Decimal(-1) : Decimal(1);
 
@@ skipping 18 matching lines @@
 
     if (exponent() >= 0)
         return *this;
 
     uint64_t result = m_data.coefficient();
     const int numberOfDigits = countDigits(result);
     const int numberOfDropDigits = -exponent();
     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);
 }
 
 Decimal Decimal::fromDouble(double doubleValue)
 {
     if (std::isfinite(doubleValue))
         return fromString(String::numberToStringECMAScript(doubleValue));
 
     if (std::isinf(doubleValue))
         return infinity(doubleValue < 0 ? Negative : Positive);
@@ skipping 338 matching lines @@
     }
     return builder.toString();
 }
 
 Decimal Decimal::zero(Sign sign)
 {
     return Decimal(EncodedData(sign, EncodedData::ClassZero));
 }
 
 } // namespace WebCore