+/*
+ * 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 "Assertions.h"
+#include "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 {
+
+class CrashOnOverflow {
+protected:
+ 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 SameType = IsSameType<Target, Source>::value> 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 = 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 = 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 (lhs == std::numeric_limits<ResultType>::min() || 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 = 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
+ {
+ ResultType temp = lhs * rhs;
+ if (temp < lhs)
+ return false;
+ result = temp;
+ 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 };
+
+// FIXME: Needed to workaround http://llvm.org/bugs/show_bug.cgi?id=10801
+static inline bool workAroundClangBug() { return true; }
+
+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)
+ {
+ // FIXME: Remove this when clang fixes http://llvm.org/bugs/show_bug.cgi?id=10801
+ if (workAroundClangBug())
+ 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;
+ }
+
+ bool safeGet(T& value) const WARN_UNUSED_RETURN
+ {
+ value = m_value;
+ return this->hasOverflowed();
+ }
+
+ // 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;
+ }
+
+ 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) || rhs.safeGet(y);
+ 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) || rhs.safeGet(y);
+ 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) || rhs.safeGet(y);
+ 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;
+}
+
+}
+
+using WTF::Checked;
+using WTF::RecordOverflow;
+
+#endif
projects / apple / javascriptcore.git / commitdiff
