From 5f8de423f190bbb79a62f804151bc24824fa32d8 Mon Sep 17 00:00:00 2001 From: "Matt A. Tobin" Date: Fri, 2 Feb 2018 04:16:08 -0500 Subject: Add m-esr52 at 52.6.0 --- mfbt/CheckedInt.h | 791 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 791 insertions(+) create mode 100644 mfbt/CheckedInt.h (limited to 'mfbt/CheckedInt.h') diff --git a/mfbt/CheckedInt.h b/mfbt/CheckedInt.h new file mode 100644 index 000000000..02ef8d5b7 --- /dev/null +++ b/mfbt/CheckedInt.h @@ -0,0 +1,791 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ +/* vim: set ts=8 sts=2 et sw=2 tw=80: */ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +/* Provides checked integers, detecting integer overflow and divide-by-0. */ + +#ifndef mozilla_CheckedInt_h +#define mozilla_CheckedInt_h + +#include +#include "mozilla/Assertions.h" +#include "mozilla/Attributes.h" +#include "mozilla/IntegerTypeTraits.h" + +namespace mozilla { + +template class CheckedInt; + +namespace detail { + +/* + * Step 1: manually record supported types + * + * What's nontrivial here is that there are different families of integer + * types: basic integer types and stdint types. It is merrily undefined which + * types from one family may be just typedefs for a type from another family. + * + * For example, on GCC 4.6, aside from the basic integer types, the only other + * type that isn't just a typedef for some of them, is int8_t. + */ + +struct UnsupportedType {}; + +template +struct IsSupportedPass2 +{ + static const bool value = false; +}; + +template +struct IsSupported +{ + static const bool value = IsSupportedPass2::value; +}; + +template<> +struct IsSupported +{ static const bool value = true; }; + +template<> +struct IsSupported +{ static const bool value = true; }; + +template<> +struct IsSupported +{ static const bool value = true; }; + +template<> +struct IsSupported +{ static const bool value = true; }; + +template<> +struct IsSupported +{ static const bool value = true; }; + +template<> +struct IsSupported +{ static const bool value = true; }; + +template<> +struct IsSupported +{ static const bool value = true; }; + +template<> +struct IsSupported +{ static const bool value = true; }; + + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +template<> +struct IsSupportedPass2 +{ static const bool value = true; }; + +/* + * Step 2: Implement the actual validity checks. + * + * Ideas taken from IntegerLib, code different. + */ + +template +struct TwiceBiggerType +{ + typedef typename detail::StdintTypeForSizeAndSignedness< + sizeof(IntegerType) * 2, + IsSigned::value + >::Type Type; +}; + +template +struct TwiceBiggerType +{ + typedef UnsupportedType Type; +}; + +template +inline bool +HasSignBit(T aX) +{ + // In C++, right bit shifts on negative values is undefined by the standard. + // Notice that signed-to-unsigned conversions are always well-defined in the + // standard, as the value congruent modulo 2**n as expected. By contrast, + // unsigned-to-signed is only well-defined if the value is representable. + return bool(typename MakeUnsigned::Type(aX) >> + PositionOfSignBit::value); +} + +// Bitwise ops may return a larger type, so it's good to use this inline +// helper guaranteeing that the result is really of type T. +template +inline T +BinaryComplement(T aX) +{ + return ~aX; +} + +template::value, + bool IsUSigned = IsSigned::value> +struct DoesRangeContainRange +{ +}; + +template +struct DoesRangeContainRange +{ + static const bool value = sizeof(T) >= sizeof(U); +}; + +template +struct DoesRangeContainRange +{ + static const bool value = sizeof(T) > sizeof(U); +}; + +template +struct DoesRangeContainRange +{ + static const bool value = false; +}; + +template::value, + bool IsUSigned = IsSigned::value, + bool DoesTRangeContainURange = DoesRangeContainRange::value> +struct IsInRangeImpl {}; + +template +struct IsInRangeImpl +{ + static bool run(U) + { + return true; + } +}; + +template +struct IsInRangeImpl +{ + static bool run(U aX) + { + return aX <= MaxValue::value && aX >= MinValue::value; + } +}; + +template +struct IsInRangeImpl +{ + static bool run(U aX) + { + return aX <= MaxValue::value; + } +}; + +template +struct IsInRangeImpl +{ + static bool run(U aX) + { + return sizeof(T) > sizeof(U) || aX <= U(MaxValue::value); + } +}; + +template +struct IsInRangeImpl +{ + static bool run(U aX) + { + return sizeof(T) >= sizeof(U) + ? aX >= 0 + : aX >= 0 && aX <= U(MaxValue::value); + } +}; + +template +inline bool +IsInRange(U aX) +{ + return IsInRangeImpl::run(aX); +} + +template +inline bool +IsAddValid(T aX, T aY) +{ + // Addition is valid if the sign of aX+aY is equal to either that of aX or + // that of aY. Since the value of aX+aY is undefined if we have a signed + // type, we compute it using the unsigned type of the same size. Beware! + // These bitwise operations can return a larger integer type, if T was a + // small type like int8_t, so we explicitly cast to T. + + typename MakeUnsigned::Type ux = aX; + typename MakeUnsigned::Type uy = aY; + typename MakeUnsigned::Type result = ux + uy; + return IsSigned::value + ? HasSignBit(BinaryComplement(T((result ^ aX) & (result ^ aY)))) + : BinaryComplement(aX) >= aY; +} + +template +inline bool +IsSubValid(T aX, T aY) +{ + // Subtraction is valid if either aX and aY have same sign, or aX-aY and aX + // have same sign. Since the value of aX-aY is undefined if we have a signed + // type, we compute it using the unsigned type of the same size. + typename MakeUnsigned::Type ux = aX; + typename MakeUnsigned::Type uy = aY; + typename MakeUnsigned::Type result = ux - uy; + + return IsSigned::value + ? HasSignBit(BinaryComplement(T((result ^ aX) & (aX ^ aY)))) + : aX >= aY; +} + +template::value, + bool TwiceBiggerTypeIsSupported = + IsSupported::Type>::value> +struct IsMulValidImpl {}; + +template +struct IsMulValidImpl +{ + static bool run(T aX, T aY) + { + typedef typename TwiceBiggerType::Type TwiceBiggerType; + TwiceBiggerType product = TwiceBiggerType(aX) * TwiceBiggerType(aY); + return IsInRange(product); + } +}; + +template +struct IsMulValidImpl +{ + static bool run(T aX, T aY) + { + const T max = MaxValue::value; + const T min = MinValue::value; + + if (aX == 0 || aY == 0) { + return true; + } + if (aX > 0) { + return aY > 0 + ? aX <= max / aY + : aY >= min / aX; + } + + // If we reach this point, we know that aX < 0. + return aY > 0 + ? aX >= min / aY + : aY >= max / aX; + } +}; + +template +struct IsMulValidImpl +{ + static bool run(T aX, T aY) + { + return aY == 0 || aX <= MaxValue::value / aY; + } +}; + +template +inline bool +IsMulValid(T aX, T aY) +{ + return IsMulValidImpl::run(aX, aY); +} + +template +inline bool +IsDivValid(T aX, T aY) +{ + // Keep in mind that in the signed case, min/-1 is invalid because + // abs(min)>max. + return aY != 0 && + !(IsSigned::value && aX == MinValue::value && aY == T(-1)); +} + +template::value> +struct IsModValidImpl; + +template +inline bool +IsModValid(T aX, T aY) +{ + return IsModValidImpl::run(aX, aY); +} + +/* + * Mod is pretty simple. + * For now, let's just use the ANSI C definition: + * If aX or aY are negative, the results are implementation defined. + * Consider these invalid. + * Undefined for aY=0. + * The result will never exceed either aX or aY. + * + * Checking that aX>=0 is a warning when T is unsigned. + */ + +template +struct IsModValidImpl +{ + static inline bool run(T aX, T aY) + { + return aY >= 1; + } +}; + +template +struct IsModValidImpl +{ + static inline bool run(T aX, T aY) + { + if (aX < 0) { + return false; + } + return aY >= 1; + } +}; + +template::value> +struct NegateImpl; + +template +struct NegateImpl +{ + static CheckedInt negate(const CheckedInt& aVal) + { + // Handle negation separately for signed/unsigned, for simpler code and to + // avoid an MSVC warning negating an unsigned value. + return CheckedInt(0, aVal.isValid() && aVal.mValue == 0); + } +}; + +template +struct NegateImpl +{ + static CheckedInt negate(const CheckedInt& aVal) + { + // Watch out for the min-value, which (with twos-complement) can't be + // negated as -min-value is then (max-value + 1). + if (!aVal.isValid() || aVal.mValue == MinValue::value) { + return CheckedInt(aVal.mValue, false); + } + return CheckedInt(-aVal.mValue, true); + } +}; + +} // namespace detail + + +/* + * Step 3: Now define the CheckedInt class. + */ + +/** + * @class CheckedInt + * @brief Integer wrapper class checking for integer overflow and other errors + * @param T the integer type to wrap. Can be any type among the following: + * - any basic integer type such as |int| + * - any stdint type such as |int8_t| + * + * This class implements guarded integer arithmetic. Do a computation, check + * that isValid() returns true, you then have a guarantee that no problem, such + * as integer overflow, happened during this computation, and you can call + * value() to get the plain integer value. + * + * The arithmetic operators in this class are guaranteed not to raise a signal + * (e.g. in case of a division by zero). + * + * For example, suppose that you want to implement a function that computes + * (aX+aY)/aZ, that doesn't crash if aZ==0, and that reports on error (divide by + * zero or integer overflow). You could code it as follows: + @code + bool computeXPlusYOverZ(int aX, int aY, int aZ, int* aResult) + { + CheckedInt checkedResult = (CheckedInt(aX) + aY) / aZ; + if (checkedResult.isValid()) { + *aResult = checkedResult.value(); + return true; + } else { + return false; + } + } + @endcode + * + * Implicit conversion from plain integers to checked integers is allowed. The + * plain integer is checked to be in range before being casted to the + * destination type. This means that the following lines all compile, and the + * resulting CheckedInts are correctly detected as valid or invalid: + * @code + // 1 is of type int, is found to be in range for uint8_t, x is valid + CheckedInt x(1); + // -1 is of type int, is found not to be in range for uint8_t, x is invalid + CheckedInt x(-1); + // -1 is of type int, is found to be in range for int8_t, x is valid + CheckedInt x(-1); + // 1000 is of type int16_t, is found not to be in range for int8_t, + // x is invalid + CheckedInt x(int16_t(1000)); + // 3123456789 is of type uint32_t, is found not to be in range for int32_t, + // x is invalid + CheckedInt x(uint32_t(3123456789)); + * @endcode + * Implicit conversion from + * checked integers to plain integers is not allowed. As shown in the + * above example, to get the value of a checked integer as a normal integer, + * call value(). + * + * Arithmetic operations between checked and plain integers is allowed; the + * result type is the type of the checked integer. + * + * Checked integers of different types cannot be used in the same arithmetic + * expression. + * + * There are convenience typedefs for all stdint types, of the following form + * (these are just 2 examples): + @code + typedef CheckedInt CheckedInt32; + typedef CheckedInt CheckedUint16; + @endcode + */ +template +class CheckedInt +{ +protected: + T mValue; + bool mIsValid; + + template + CheckedInt(U aValue, bool aIsValid) : mValue(aValue), mIsValid(aIsValid) + { + static_assert(detail::IsSupported::value && + detail::IsSupported::value, + "This type is not supported by CheckedInt"); + } + + friend struct detail::NegateImpl; + +public: + /** + * Constructs a checked integer with given @a value. The checked integer is + * initialized as valid or invalid depending on whether the @a value + * is in range. + * + * This constructor is not explicit. Instead, the type of its argument is a + * separate template parameter, ensuring that no conversion is performed + * before this constructor is actually called. As explained in the above + * documentation for class CheckedInt, this constructor checks that its + * argument is valid. + */ + template + MOZ_IMPLICIT CheckedInt(U aValue) MOZ_NO_ARITHMETIC_EXPR_IN_ARGUMENT + : mValue(T(aValue)), + mIsValid(detail::IsInRange(aValue)) + { + static_assert(detail::IsSupported::value && + detail::IsSupported::value, + "This type is not supported by CheckedInt"); + } + + template + friend class CheckedInt; + + template + CheckedInt toChecked() const + { + CheckedInt ret(mValue); + ret.mIsValid = ret.mIsValid && mIsValid; + return ret; + } + + /** Constructs a valid checked integer with initial value 0 */ + CheckedInt() : mValue(0), mIsValid(true) + { + static_assert(detail::IsSupported::value, + "This type is not supported by CheckedInt"); + } + + /** @returns the actual value */ + T value() const + { + MOZ_ASSERT(mIsValid, "Invalid checked integer (division by zero or integer overflow)"); + return mValue; + } + + /** + * @returns true if the checked integer is valid, i.e. is not the result + * of an invalid operation or of an operation involving an invalid checked + * integer + */ + bool isValid() const + { + return mIsValid; + } + + template + friend CheckedInt operator +(const CheckedInt& aLhs, + const CheckedInt& aRhs); + template + CheckedInt& operator +=(U aRhs); + CheckedInt& operator +=(const CheckedInt& aRhs); + + template + friend CheckedInt operator -(const CheckedInt& aLhs, + const CheckedInt& aRhs); + template + CheckedInt& operator -=(U aRhs); + CheckedInt& operator -=(const CheckedInt& aRhs); + + template + friend CheckedInt operator *(const CheckedInt& aLhs, + const CheckedInt& aRhs); + template + CheckedInt& operator *=(U aRhs); + CheckedInt& operator *=(const CheckedInt& aRhs); + + template + friend CheckedInt operator /(const CheckedInt& aLhs, + const CheckedInt& aRhs); + template + CheckedInt& operator /=(U aRhs); + CheckedInt& operator /=(const CheckedInt& aRhs); + + template + friend CheckedInt operator %(const CheckedInt& aLhs, + const CheckedInt& aRhs); + template + CheckedInt& operator %=(U aRhs); + CheckedInt& operator %=(const CheckedInt& aRhs); + + CheckedInt operator -() const + { + return detail::NegateImpl::negate(*this); + } + + /** + * @returns true if the left and right hand sides are valid + * and have the same value. + * + * Note that these semantics are the reason why we don't offer + * a operator!=. Indeed, we'd want to have a!=b be equivalent to !(a==b) + * but that would mean that whenever a or b is invalid, a!=b + * is always true, which would be very confusing. + * + * For similar reasons, operators <, >, <=, >= would be very tricky to + * specify, so we just avoid offering them. + * + * Notice that these == semantics are made more reasonable by these facts: + * 1. a==b implies equality at the raw data level + * (the converse is false, as a==b is never true among invalids) + * 2. This is similar to the behavior of IEEE floats, where a==b + * means that a and b have the same value *and* neither is NaN. + */ + bool operator ==(const CheckedInt& aOther) const + { + return mIsValid && aOther.mIsValid && mValue == aOther.mValue; + } + + /** prefix ++ */ + CheckedInt& operator++() + { + *this += 1; + return *this; + } + + /** postfix ++ */ + CheckedInt operator++(int) + { + CheckedInt tmp = *this; + *this += 1; + return tmp; + } + + /** prefix -- */ + CheckedInt& operator--() + { + *this -= 1; + return *this; + } + + /** postfix -- */ + CheckedInt operator--(int) + { + CheckedInt tmp = *this; + *this -= 1; + return tmp; + } + +private: + /** + * The !=, <, <=, >, >= operators are disabled: + * see the comment on operator==. + */ + template bool operator !=(U aOther) const = delete; + template bool operator < (U aOther) const = delete; + template bool operator <=(U aOther) const = delete; + template bool operator > (U aOther) const = delete; + template bool operator >=(U aOther) const = delete; +}; + +#define MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(NAME, OP) \ + template \ + inline CheckedInt \ + operator OP(const CheckedInt& aLhs, const CheckedInt& aRhs) \ + { \ + if (!detail::Is##NAME##Valid(aLhs.mValue, aRhs.mValue)) { \ + return CheckedInt(0, false); \ + } \ + return CheckedInt(aLhs.mValue OP aRhs.mValue, \ + aLhs.mIsValid && aRhs.mIsValid); \ + } + +MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Add, +) +MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Sub, -) +MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Mul, *) +MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Div, /) +MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(Mod, %) + +#undef MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR + +// Implement castToCheckedInt(x), making sure that +// - it allows x to be either a CheckedInt or any integer type +// that can be casted to T +// - if x is already a CheckedInt, we just return a reference to it, +// instead of copying it (optimization) + +namespace detail { + +template +struct CastToCheckedIntImpl +{ + typedef CheckedInt ReturnType; + static CheckedInt run(U aU) { return aU; } +}; + +template +struct CastToCheckedIntImpl > +{ + typedef const CheckedInt& ReturnType; + static const CheckedInt& run(const CheckedInt& aU) { return aU; } +}; + +} // namespace detail + +template +inline typename detail::CastToCheckedIntImpl::ReturnType +castToCheckedInt(U aU) +{ + static_assert(detail::IsSupported::value && + detail::IsSupported::value, + "This type is not supported by CheckedInt"); + return detail::CastToCheckedIntImpl::run(aU); +} + +#define MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(OP, COMPOUND_OP) \ + template \ + template \ + CheckedInt& CheckedInt::operator COMPOUND_OP(U aRhs) \ + { \ + *this = *this OP castToCheckedInt(aRhs); \ + return *this; \ + } \ + template \ + CheckedInt& CheckedInt::operator COMPOUND_OP(const CheckedInt& aRhs) \ + { \ + *this = *this OP aRhs; \ + return *this; \ + } \ + template \ + inline CheckedInt operator OP(const CheckedInt& aLhs, U aRhs) \ + { \ + return aLhs OP castToCheckedInt(aRhs); \ + } \ + template \ + inline CheckedInt operator OP(U aLhs, const CheckedInt& aRhs) \ + { \ + return castToCheckedInt(aLhs) OP aRhs; \ + } + +MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(+, +=) +MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(*, *=) +MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(-, -=) +MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(/, /=) +MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(%, %=) + +#undef MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS + +template +inline bool +operator ==(const CheckedInt& aLhs, U aRhs) +{ + return aLhs == castToCheckedInt(aRhs); +} + +template +inline bool +operator ==(U aLhs, const CheckedInt& aRhs) +{ + return castToCheckedInt(aLhs) == aRhs; +} + +// Convenience typedefs. +typedef CheckedInt CheckedInt8; +typedef CheckedInt CheckedUint8; +typedef CheckedInt CheckedInt16; +typedef CheckedInt CheckedUint16; +typedef CheckedInt CheckedInt32; +typedef CheckedInt CheckedUint32; +typedef CheckedInt CheckedInt64; +typedef CheckedInt CheckedUint64; + +} // namespace mozilla + +#endif /* mozilla_CheckedInt_h */ -- cgit v1.2.3