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 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-

  * vim: set ts=8 sts=4 et sw=4 tw=99:

  *

  * 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,

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  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR

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  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

  */

 #ifndef yarr_CheckedArithmetic_h

 #define yarr_CheckedArithmetic_h

 #include "assembler/wtf/Assertions.h"

 #include <limits>

 #include <stdint.h>

 #include "mozilla/TypeTraits.h"

 #ifdef _MSC_VER

 # undef min

 # undef max

 #endif

 /* 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 = RecordOverflow> 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 = mozilla::IsSame<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;

     }

     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) || 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 /* yarr_CheckedArithmetic_h */