Revert of wtf/CheckedArithmetic.h delegates to base/numerics/safe_math.h.

third_party/WebKit/Source/wtf/CheckedArithmetic.h

+/*
+ * Copyright (C) 2011 Apple 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:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
+ * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef CheckedArithmetic_h
+#define CheckedArithmetic_h
+
+#include "wtf/Assertions.h"
+#include "wtf/TypeTraits.h"
+
+#include <limits>
+#include <stdint.h>
+
+/* Checked<T>
+ *
+ * This class provides a mechanism to perform overflow-safe integer arithmetic
+ * without having to manually ensure that you have all the required bounds checks
+ * directly in your code.
+ *
+ * There are two modes of operation:
+ *  - The default is Checked<T, CrashOnOverflow>, and crashes at the point
+ *    and overflow has occurred.
+ *  - The alternative is Checked<T, RecordOverflow>, which uses an additional
+ *    byte of storage to track whether an overflow has occurred, subsequent
+ *    unchecked operations will crash if an overflow has occured
+ *
+ * It is possible to provide a custom overflow handler, in which case you need
+ * to support these functions:
+ *  - void overflowed();
+ *    This function is called when an operation has produced an overflow.
+ *  - bool hasOverflowed();
+ *    This function must return true if overflowed() has been called on an
+ *    instance and false if it has not.
+ *  - void clearOverflow();
+ *    Used to reset overflow tracking when a value is being overwritten with
+ *    a new value.
+ *
+ * Checked<T> works for all integer types, with the following caveats:
+ *  - Mixing signedness of operands is only supported for types narrower than
+ *    64bits.
+ *  - It does have a performance impact, so tight loops may want to be careful
+ *    when using it.
+ *
+ */
+
+namespace WTF {
+
+enum class CheckedState {
+    DidOverflow,
+    DidNotOverflow
+};
+
+class CrashOnOverflow {
+protected:
+    NO_RETURN_DUE_TO_CRASH void overflowed()
+    {
+        CRASH();
+    }
+
+    void clearOverflow() { }
+
+public:
+    bool hasOverflowed() const { return false; }
+};
+
+class RecordOverflow {
+protected:
+    RecordOverflow()
+        : m_overflowed(false)
+    {
+    }
+
+    void overflowed()
+    {
+        m_overflowed = true;
+    }
+
+    void clearOverflow()
+    {
+        m_overflowed = false;
+    }
+
+public:
+    bool hasOverflowed() const { return m_overflowed; }
+
+private:
+    unsigned char m_overflowed;
+};
+
+template <typename T, class OverflowHandler = CrashOnOverflow> class Checked;
+template <typename T> struct RemoveChecked;
+template <typename T> struct RemoveChecked<Checked<T>>;
+
+template <typename Target, typename Source, bool targetSigned = std::numeric_limits<Target>::is_signed, bool sourceSigned = std::numeric_limits<Source>::is_signed> struct BoundsChecker;
+template <typename Target, typename Source> struct BoundsChecker<Target, Source, false, false> {
+    static bool inBounds(Source value)
+    {
+        // Same signedness so implicit type conversion will always increase precision
+        // to widest type
+        return value <= std::numeric_limits<Target>::max();
+    }
+};
+
+template <typename Target, typename Source> struct BoundsChecker<Target, Source, true, true> {
+    static bool inBounds(Source value)
+    {
+        // Same signedness so implicit type conversion will always increase precision
+        // to widest type
+        return std::numeric_limits<Target>::min() <= value && value <= std::numeric_limits<Target>::max();
+    }
+};
+
+template <typename Target, typename Source> struct BoundsChecker<Target, Source, false, true> {
+    static bool inBounds(Source value)
+    {
+        // Target is unsigned so any value less than zero is clearly unsafe
+        if (value < 0)
+            return false;
+        // If our (unsigned) Target is the same or greater width we can
+        // convert value to type Target without losing precision
+        if (sizeof(Target) >= sizeof(Source))
+            return static_cast<Target>(value) <= std::numeric_limits<Target>::max();
+        // The signed Source type has greater precision than the target so
+        // max(Target) -> Source will widen.
+        return value <= static_cast<Source>(std::numeric_limits<Target>::max());
+    }
+};
+
+template <typename Target, typename Source> struct BoundsChecker<Target, Source, true, false> {
+    static bool inBounds(Source value)
+    {
+        // Signed target with an unsigned source
+        if (sizeof(Target) <= sizeof(Source))
+            return value <= static_cast<Source>(std::numeric_limits<Target>::max());
+        // Target is Wider than Source so we're guaranteed to fit any value in
+        // unsigned Source
+        return true;
+    }
+};
+
+template <typename Target, typename Source, bool CanElide = std::is_same<Target, Source>::value || (sizeof(Target) > sizeof(Source)) > struct BoundsCheckElider;
+template <typename Target, typename Source> struct BoundsCheckElider<Target, Source, true> {
+    static bool inBounds(Source) { return true; }
+};
+template <typename Target, typename Source> struct BoundsCheckElider<Target, Source, false> : public BoundsChecker<Target, Source> {
+};
+
+template <typename Target, typename Source> static inline bool isInBounds(Source value)
+{
+    return BoundsCheckElider<Target, Source>::inBounds(value);
+}
+
+template <typename T> struct RemoveChecked {
+    typedef T CleanType;
+    static const CleanType DefaultValue = 0;
+};
+
+template <typename T> struct RemoveChecked<Checked<T, CrashOnOverflow>> {
+    typedef typename RemoveChecked<T>::CleanType CleanType;
+    static const CleanType DefaultValue = 0;
+};
+
+template <typename T> struct RemoveChecked<Checked<T, RecordOverflow>> {
+    typedef typename RemoveChecked<T>::CleanType CleanType;
+    static const CleanType DefaultValue = 0;
+};
+
+// The ResultBase and SignednessSelector are used to workaround typeof not being
+// available in MSVC
+template <typename U, typename V, bool uIsBigger = (sizeof(U) > sizeof(V)), bool sameSize = (sizeof(U) == sizeof(V))> struct ResultBase;
+template <typename U, typename V> struct ResultBase<U, V, true, false> {
+    typedef U ResultType;
+};
+
+template <typename U, typename V> struct ResultBase<U, V, false, false> {
+    typedef V ResultType;
+};
+
+template <typename U> struct ResultBase<U, U, false, true> {
+    typedef U ResultType;
+};
+
+template <typename U, typename V, bool uIsSigned = std::numeric_limits<U>::is_signed, bool vIsSigned = std::numeric_limits<V>::is_signed> struct SignednessSelector;
+template <typename U, typename V> struct SignednessSelector<U, V, true, true> {
+    typedef U ResultType;
+};
+
+template <typename U, typename V> struct SignednessSelector<U, V, false, false> {
+    typedef U ResultType;
+};
+
+template <typename U, typename V> struct SignednessSelector<U, V, true, false> {
+    typedef V ResultType;
+};
+
+template <typename U, typename V> struct SignednessSelector<U, V, false, true> {
+    typedef U ResultType;
+};
+
+template <typename U, typename V> struct ResultBase<U, V, false, true> {
+    typedef typename SignednessSelector<U, V>::ResultType ResultType;
+};
+
+template <typename U, typename V> struct Result : ResultBase<typename RemoveChecked<U>::CleanType, typename RemoveChecked<V>::CleanType> {
+};
+
+template <typename LHS, typename RHS, typename ResultType = typename Result<LHS, RHS>::ResultType,
+    bool lhsSigned = std::numeric_limits<LHS>::is_signed, bool rhsSigned = std::numeric_limits<RHS>::is_signed> struct ArithmeticOperations;
+
+template <typename LHS, typename RHS, typename ResultType> struct ArithmeticOperations<LHS, RHS, ResultType, true, true> {
+    // LHS and RHS are signed types
+
+    // Helper function
+    static inline bool signsMatch(LHS lhs, RHS rhs)
+    {
+        return (lhs ^ rhs) >= 0;
+    }
+
+    static inline bool add(LHS lhs, RHS rhs, ResultType& result) WARN_UNUSED_RETURN
+    {
+        if (signsMatch(lhs, rhs)) {
+            if (lhs >= 0) {
+                if ((std::numeric_limits<ResultType>::max() - rhs) < lhs)
+                    return false;
+            } else {
+                ResultType temp = lhs - std::numeric_limits<ResultType>::min();
+                if (rhs < -temp)
+                    return false;
+            }
+        } // if the signs do not match this operation can't overflow
+        result = static_cast<ResultType>(lhs + rhs);
+        return true;
+    }
+
+    static inline bool sub(LHS lhs, RHS rhs, ResultType& result) WARN_UNUSED_RETURN
+    {
+        if (!signsMatch(lhs, rhs)) {
+            if (lhs >= 0) {
+                if (lhs > std::numeric_limits<ResultType>::max() + rhs)
+                    return false;
+            } else {
+                if (rhs > std::numeric_limits<ResultType>::max() + lhs)
+                    return false;
+            }
+        } // if the signs match this operation can't overflow
+        result = static_cast<ResultType>(lhs - rhs);
+        return true;
+    }
+
+    static inline bool multiply(LHS lhs, RHS rhs, ResultType& result) WARN_UNUSED_RETURN
+    {
+        if (signsMatch(lhs, rhs)) {
+            if (lhs >= 0) {
+                if (lhs && (std::numeric_limits<ResultType>::max() / lhs) < rhs)
+                    return false;
+            } else {
+                if (static_cast<ResultType>(lhs) == std::numeric_limits<ResultType>::min() || static_cast<ResultType>(rhs) == std::numeric_limits<ResultType>::min())
+                    return false;
+                if ((std::numeric_limits<ResultType>::max() / -lhs) < -rhs)
+                    return false;
+            }
+        } else {
+            if (lhs < 0) {
+                if (rhs && lhs < (std::numeric_limits<ResultType>::min() / rhs))
+                    return false;
+            } else {
+                if (lhs && rhs < (std::numeric_limits<ResultType>::min() / lhs))
+                    return false;
+            }
+        }
+        result = static_cast<ResultType>(lhs * rhs);
+        return true;
+    }
+
+    static inline bool equals(LHS lhs, RHS rhs) { return lhs == rhs; }
+
+};
+
+template <typename LHS, typename RHS, typename ResultType> struct ArithmeticOperations<LHS, RHS, ResultType, false, false> {
+    // LHS and RHS are unsigned types so bounds checks are nice and easy
+    static inline bool add(LHS lhs, RHS rhs, ResultType& result) WARN_UNUSED_RETURN
+    {
+        ResultType temp = lhs + rhs;
+        if (temp < lhs)
+            return false;
+        result = temp;
+        return true;
+    }
+
+    static inline bool sub(LHS lhs, RHS rhs, ResultType& result) WARN_UNUSED_RETURN
+    {
+        ResultType temp = lhs - rhs;
+        if (temp > lhs)
+            return false;
+        result = temp;
+        return true;
+    }
+
+    static inline bool multiply(LHS lhs, RHS rhs, ResultType& result) WARN_UNUSED_RETURN
+    {
+        if (!lhs || !rhs) {
+            result = 0;
+            return true;
+        }
+        if (std::numeric_limits<ResultType>::max() / lhs < rhs)
+            return false;
+        result = lhs * rhs;
+        return true;
+    }
+
+    static inline bool equals(LHS lhs, RHS rhs) { return lhs == rhs; }
+
+};
+
+template <typename ResultType> struct ArithmeticOperations<int, unsigned, ResultType, true, false> {
+    static inline bool add(int64_t lhs, int64_t rhs, ResultType& result)
+    {
+        int64_t temp = lhs + rhs;
+        if (temp < std::numeric_limits<ResultType>::min())
+            return false;
+        if (temp > std::numeric_limits<ResultType>::max())
+            return false;
+        result = static_cast<ResultType>(temp);
+        return true;
+    }
+
+    static inline bool sub(int64_t lhs, int64_t rhs, ResultType& result)
+    {
+        int64_t temp = lhs - rhs;
+        if (temp < std::numeric_limits<ResultType>::min())
+            return false;
+        if (temp > std::numeric_limits<ResultType>::max())
+            return false;
+        result = static_cast<ResultType>(temp);
+        return true;
+    }
+
+    static inline bool multiply(int64_t lhs, int64_t rhs, ResultType& result)
+    {
+        int64_t temp = lhs * rhs;
+        if (temp < std::numeric_limits<ResultType>::min())
+            return false;
+        if (temp > std::numeric_limits<ResultType>::max())
+            return false;
+        result = static_cast<ResultType>(temp);
+        return true;
+    }
+
+    static inline bool equals(int lhs, unsigned rhs)
+    {
+        return static_cast<int64_t>(lhs) == static_cast<int64_t>(rhs);
+    }
+};
+
+template <typename ResultType> struct ArithmeticOperations<unsigned, int, ResultType, false, true> {
+    static inline bool add(int64_t lhs, int64_t rhs, ResultType& result)
+    {
+        return ArithmeticOperations<int, unsigned, ResultType>::add(rhs, lhs, result);
+    }
+
+    static inline bool sub(int64_t lhs, int64_t rhs, ResultType& result)
+    {
+        return ArithmeticOperations<int, unsigned, ResultType>::sub(lhs, rhs, result);
+    }
+
+    static inline bool multiply(int64_t lhs, int64_t rhs, ResultType& result)
+    {
+        return ArithmeticOperations<int, unsigned, ResultType>::multiply(rhs, lhs, result);
+    }
+
+    static inline bool equals(unsigned lhs, int rhs)
+    {
+        return ArithmeticOperations<int, unsigned, ResultType>::equals(rhs, lhs);
+    }
+};
+
+template <typename U, typename V, typename R> static inline bool safeAdd(U lhs, V rhs, R& result)
+{
+    return ArithmeticOperations<U, V, R>::add(lhs, rhs, result);
+}
+
+template <typename U, typename V, typename R> static inline bool safeSub(U lhs, V rhs, R& result)
+{
+    return ArithmeticOperations<U, V, R>::sub(lhs, rhs, result);
+}
+
+template <typename U, typename V, typename R> static inline bool safeMultiply(U lhs, V rhs, R& result)
+{
+    return ArithmeticOperations<U, V, R>::multiply(lhs, rhs, result);
+}
+
+template <typename U, typename V> static inline bool safeEquals(U lhs, V rhs)
+{
+    return ArithmeticOperations<U, V>::equals(lhs, rhs);
+}
+
+enum ResultOverflowedTag { ResultOverflowed };
+
+template <typename T, class OverflowHandler> class Checked : public OverflowHandler {
+public:
+    template <typename _T, class _OverflowHandler> friend class Checked;
+    Checked()
+        : m_value(0)
+    {
+    }
+
+    Checked(ResultOverflowedTag)
+        : m_value(0)
+    {
+        this->overflowed();
+    }
+
+    template <typename U> Checked(U value)
+    {
+        if (!isInBounds<T>(value))
+            this->overflowed();
+        m_value = static_cast<T>(value);
+    }
+
+    template <typename V> Checked(const Checked<T, V>& rhs)
+        : m_value(rhs.m_value)
+    {
+        if (rhs.hasOverflowed())
+            this->overflowed();
+    }
+
+    template <typename U> Checked(const Checked<U, OverflowHandler>& rhs)
+        : OverflowHandler(rhs)
+    {
+        if (!isInBounds<T>(rhs.m_value))
+            this->overflowed();
+        m_value = static_cast<T>(rhs.m_value);
+    }
+
+    template <typename U, typename V> Checked(const Checked<U, V>& rhs)
+    {
+        if (rhs.hasOverflowed())
+            this->overflowed();
+        if (!isInBounds<T>(rhs.m_value))
+            this->overflowed();
+        m_value = static_cast<T>(rhs.m_value);
+    }
+
+    const Checked& operator=(Checked rhs)
+    {
+        this->clearOverflow();
+        if (rhs.hasOverflowed())
+            this->overflowed();
+        m_value = static_cast<T>(rhs.m_value);
+        return *this;
+    }
+
+    template <typename U> const Checked& operator=(U value)
+    {
+        return *this = Checked(value);
+    }
+
+    template <typename U, typename V> const Checked& operator=(const Checked<U, V>& rhs)
+    {
+        return *this = Checked(rhs);
+    }
+
+    // prefix
+    const Checked& operator++()
+    {
+        if (m_value == std::numeric_limits<T>::max())
+            this->overflowed();
+        m_value++;
+        return *this;
+    }
+
+    const Checked& operator--()
+    {
+        if (m_value == std::numeric_limits<T>::min())
+            this->overflowed();
+        m_value--;
+        return *this;
+    }
+
+    // postfix operators
+    const Checked operator++(int)
+    {
+        if (m_value == std::numeric_limits<T>::max())
+            this->overflowed();
+        return Checked(m_value++);
+    }
+
+    const Checked operator--(int)
+    {
+        if (m_value == std::numeric_limits<T>::min())
+            this->overflowed();
+        return Checked(m_value--);
+    }
+
+    // Boolean operators
+    bool operator!() const
+    {
+        if (this->hasOverflowed())
+            CRASH();
+        return !m_value;
+    }
+
+    typedef void* (Checked::*UnspecifiedBoolType);
+    operator UnspecifiedBoolType*() const
+    {
+        if (this->hasOverflowed())
+            CRASH();
+        return (m_value) ? reinterpret_cast<UnspecifiedBoolType*>(1) : 0;
+    }
+
+    // Value accessors. unsafeGet() will crash if there's been an overflow.
+    T unsafeGet() const
+    {
+        if (this->hasOverflowed())
+            CRASH();
+        return m_value;
+    }
+
+    inline CheckedState safeGet(T& value) const WARN_UNUSED_RETURN
+    {
+        value = m_value;
+        if (this->hasOverflowed())
+            return CheckedState::DidOverflow;
+        return CheckedState::DidNotOverflow;
+    }
+
+    // Mutating assignment
+    template <typename U> const Checked operator+=(U rhs)
+    {
+        if (!safeAdd(m_value, rhs, m_value))
+            this->overflowed();
+        return *this;
+    }
+
+    template <typename U> const Checked operator-=(U rhs)
+    {
+        if (!safeSub(m_value, rhs, m_value))
+            this->overflowed();
+        return *this;
+    }
+
+    template <typename U> const Checked operator*=(U rhs)
+    {
+        if (!safeMultiply(m_value, rhs, m_value))
+            this->overflowed();
+        return *this;
+    }
+
+    const Checked operator*=(double rhs)
+    {
+        double result = rhs * m_value;
+        // Handle +/- infinity and NaN
+        if (!(std::numeric_limits<T>::min() <= result && std::numeric_limits<T>::max() >= result))
+            this->overflowed();
+        m_value = (T)result;
+        return *this;
+    }
+
+    const Checked operator*=(float rhs)
+    {
+        return *this *= (double)rhs;
+    }
+
+    template <typename U, typename V> const Checked operator+=(Checked<U, V> rhs)
+    {
+        if (rhs.hasOverflowed())
+            this->overflowed();
+        return *this += rhs.m_value;
+    }
+
+    template <typename U, typename V> const Checked operator-=(Checked<U, V> rhs)
+    {
+        if (rhs.hasOverflowed())
+            this->overflowed();
+        return *this -= rhs.m_value;
+    }
+
+    template <typename U, typename V> const Checked operator*=(Checked<U, V> rhs)
+    {
+        if (rhs.hasOverflowed())
+            this->overflowed();
+        return *this *= rhs.m_value;
+    }
+
+    // Equality comparisons
+    template <typename V> bool operator==(Checked<T, V> rhs)
+    {
+        return unsafeGet() == rhs.unsafeGet();
+    }
+
+    template <typename U> bool operator==(U rhs)
+    {
+        if (this->hasOverflowed())
+            this->overflowed();
+        return safeEquals(m_value, rhs);
+    }
+
+    template <typename U, typename V> const Checked operator==(Checked<U, V> rhs)
+    {
+        return unsafeGet() == Checked(rhs.unsafeGet());
+    }
+
+    template <typename U> bool operator!=(U rhs)
+    {
+        return !(*this == rhs);
+    }
+
+private:
+    // Disallow implicit conversion of floating point to integer types
+    Checked(float);
+    Checked(double);
+    void operator=(float);
+    void operator=(double);
+    void operator+=(float);
+    void operator+=(double);
+    void operator-=(float);
+    void operator-=(double);
+    T m_value;
+};
+
+template <typename U, typename V, typename OverflowHandler> static inline Checked<typename Result<U, V>::ResultType, OverflowHandler> operator+(Checked<U, OverflowHandler> lhs, Checked<V, OverflowHandler> rhs)
+{
+    U x = 0;
+    V y = 0;
+    bool overflowed = lhs.safeGet(x) == CheckedState::DidOverflow || rhs.safeGet(y) == CheckedState::DidOverflow;
+    typename Result<U, V>::ResultType result = 0;
+    overflowed |= !safeAdd(x, y, result);
+    if (overflowed)
+        return ResultOverflowed;
+    return result;
+}
+
+template <typename U, typename V, typename OverflowHandler> static inline Checked<typename Result<U, V>::ResultType, OverflowHandler> operator-(Checked<U, OverflowHandler> lhs, Checked<V, OverflowHandler> rhs)
+{
+    U x = 0;
+    V y = 0;
+    bool overflowed = lhs.safeGet(x) == CheckedState::DidOverflow || rhs.safeGet(y) == CheckedState::DidOverflow;
+    typename Result<U, V>::ResultType result = 0;
+    overflowed |= !safeSub(x, y, result);
+    if (overflowed)
+        return ResultOverflowed;
+    return result;
+}
+
+template <typename U, typename V, typename OverflowHandler> static inline Checked<typename Result<U, V>::ResultType, OverflowHandler> operator*(Checked<U, OverflowHandler> lhs, Checked<V, OverflowHandler> rhs)
+{
+    U x = 0;
+    V y = 0;
+    bool overflowed = lhs.safeGet(x) == CheckedState::DidOverflow || rhs.safeGet(y) == CheckedState::DidOverflow;
+    typename Result<U, V>::ResultType result = 0;
+    overflowed |= !safeMultiply(x, y, result);
+    if (overflowed)
+        return ResultOverflowed;
+    return result;
+}
+
+template <typename U, typename V, typename OverflowHandler> static inline Checked<typename Result<U, V>::ResultType, OverflowHandler> operator+(Checked<U, OverflowHandler> lhs, V rhs)
+{
+    return lhs + Checked<V, OverflowHandler>(rhs);
+}
+
+template <typename U, typename V, typename OverflowHandler> static inline Checked<typename Result<U, V>::ResultType, OverflowHandler> operator-(Checked<U, OverflowHandler> lhs, V rhs)
+{
+    return lhs - Checked<V, OverflowHandler>(rhs);
+}
+
+template <typename U, typename V, typename OverflowHandler> static inline Checked<typename Result<U, V>::ResultType, OverflowHandler> operator*(Checked<U, OverflowHandler> lhs, V rhs)
+{
+    return lhs * Checked<V, OverflowHandler>(rhs);
+}
+
+template <typename U, typename V, typename OverflowHandler> static inline Checked<typename Result<U, V>::ResultType, OverflowHandler> operator+(U lhs, Checked<V, OverflowHandler> rhs)
+{
+    return Checked<U, OverflowHandler>(lhs) + rhs;
+}
+
+template <typename U, typename V, typename OverflowHandler> static inline Checked<typename Result<U, V>::ResultType, OverflowHandler> operator-(U lhs, Checked<V, OverflowHandler> rhs)
+{
+    return Checked<U, OverflowHandler>(lhs) - rhs;
+}
+
+template <typename U, typename V, typename OverflowHandler> static inline Checked<typename Result<U, V>::ResultType, OverflowHandler> operator*(U lhs, Checked<V, OverflowHandler> rhs)
+{
+    return Checked<U, OverflowHandler>(lhs) * rhs;
+}
+
+} // namespace WTF
+
+using WTF::Checked;
+using WTF::CheckedState;
+using WTF::RecordOverflow;
+
+#endif