mirror of
https://github.com/mozilla/gecko-dev.git
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780 lines
22 KiB
C++
780 lines
22 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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/* Provides checked integers, detecting integer overflow and divide-by-0. */
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#ifndef mozilla_CheckedInt_h
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#define mozilla_CheckedInt_h
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#include <stdint.h>
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#include "mozilla/Assertions.h"
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#include "mozilla/IntegerTypeTraits.h"
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namespace mozilla {
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template<typename T> class CheckedInt;
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namespace detail {
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/*
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* Step 1: manually record supported types
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*
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* What's nontrivial here is that there are different families of integer
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* types: basic integer types and stdint types. It is merrily undefined which
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* types from one family may be just typedefs for a type from another family.
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*
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* For example, on GCC 4.6, aside from the basic integer types, the only other
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* type that isn't just a typedef for some of them, is int8_t.
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*/
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struct UnsupportedType {};
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template<typename IntegerType>
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struct IsSupportedPass2
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{
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static const bool value = false;
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};
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template<typename IntegerType>
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struct IsSupported
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{
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static const bool value = IsSupportedPass2<IntegerType>::value;
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};
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template<>
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struct IsSupported<int8_t>
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{ static const bool value = true; };
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template<>
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struct IsSupported<uint8_t>
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{ static const bool value = true; };
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template<>
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struct IsSupported<int16_t>
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{ static const bool value = true; };
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template<>
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struct IsSupported<uint16_t>
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{ static const bool value = true; };
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template<>
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struct IsSupported<int32_t>
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{ static const bool value = true; };
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template<>
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struct IsSupported<uint32_t>
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{ static const bool value = true; };
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template<>
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struct IsSupported<int64_t>
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{ static const bool value = true; };
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template<>
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struct IsSupported<uint64_t>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<char>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<signed char>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<unsigned char>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<short>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<unsigned short>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<int>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<unsigned int>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<long>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<unsigned long>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<long long>
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{ static const bool value = true; };
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template<>
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struct IsSupportedPass2<unsigned long long>
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{ static const bool value = true; };
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/*
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* Step 2: Implement the actual validity checks.
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*
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* Ideas taken from IntegerLib, code different.
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*/
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template<typename IntegerType, size_t Size = sizeof(IntegerType)>
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struct TwiceBiggerType
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{
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typedef typename detail::StdintTypeForSizeAndSignedness<
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sizeof(IntegerType) * 2,
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IsSigned<IntegerType>::value
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>::Type Type;
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};
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template<typename IntegerType>
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struct TwiceBiggerType<IntegerType, 8>
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{
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typedef UnsupportedType Type;
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};
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template<typename T>
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inline bool
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HasSignBit(T aX)
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{
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// In C++, right bit shifts on negative values is undefined by the standard.
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// Notice that signed-to-unsigned conversions are always well-defined in the
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// standard, as the value congruent modulo 2**n as expected. By contrast,
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// unsigned-to-signed is only well-defined if the value is representable.
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return bool(typename MakeUnsigned<T>::Type(aX) >>
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PositionOfSignBit<T>::value);
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}
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// Bitwise ops may return a larger type, so it's good to use this inline
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// helper guaranteeing that the result is really of type T.
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template<typename T>
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inline T
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BinaryComplement(T aX)
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{
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return ~aX;
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}
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template<typename T,
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typename U,
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bool IsTSigned = IsSigned<T>::value,
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bool IsUSigned = IsSigned<U>::value>
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struct DoesRangeContainRange
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{
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};
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template<typename T, typename U, bool Signedness>
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struct DoesRangeContainRange<T, U, Signedness, Signedness>
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{
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static const bool value = sizeof(T) >= sizeof(U);
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};
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template<typename T, typename U>
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struct DoesRangeContainRange<T, U, true, false>
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{
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static const bool value = sizeof(T) > sizeof(U);
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};
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template<typename T, typename U>
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struct DoesRangeContainRange<T, U, false, true>
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{
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static const bool value = false;
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};
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template<typename T,
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typename U,
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bool IsTSigned = IsSigned<T>::value,
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bool IsUSigned = IsSigned<U>::value,
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bool DoesTRangeContainURange = DoesRangeContainRange<T, U>::value>
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struct IsInRangeImpl {};
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template<typename T, typename U, bool IsTSigned, bool IsUSigned>
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struct IsInRangeImpl<T, U, IsTSigned, IsUSigned, true>
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{
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static bool run(U)
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{
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return true;
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}
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};
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template<typename T, typename U>
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struct IsInRangeImpl<T, U, true, true, false>
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{
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static bool run(U aX)
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{
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return aX <= MaxValue<T>::value && aX >= MinValue<T>::value;
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}
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};
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template<typename T, typename U>
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struct IsInRangeImpl<T, U, false, false, false>
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{
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static bool run(U aX)
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{
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return aX <= MaxValue<T>::value;
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}
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};
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template<typename T, typename U>
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struct IsInRangeImpl<T, U, true, false, false>
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{
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static bool run(U aX)
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{
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return sizeof(T) > sizeof(U) || aX <= U(MaxValue<T>::value);
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}
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};
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template<typename T, typename U>
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struct IsInRangeImpl<T, U, false, true, false>
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{
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static bool run(U aX)
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{
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return sizeof(T) >= sizeof(U)
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? aX >= 0
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: aX >= 0 && aX <= U(MaxValue<T>::value);
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}
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};
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template<typename T, typename U>
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inline bool
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IsInRange(U aX)
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{
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return IsInRangeImpl<T, U>::run(aX);
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}
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template<typename T>
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inline bool
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IsAddValid(T aX, T aY)
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{
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// Addition is valid if the sign of aX+aY is equal to either that of aX or
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// that of aY. Since the value of aX+aY is undefined if we have a signed
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// type, we compute it using the unsigned type of the same size. Beware!
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// These bitwise operations can return a larger integer type, if T was a
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// small type like int8_t, so we explicitly cast to T.
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typename MakeUnsigned<T>::Type ux = aX;
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typename MakeUnsigned<T>::Type uy = aY;
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typename MakeUnsigned<T>::Type result = ux + uy;
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return IsSigned<T>::value
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? HasSignBit(BinaryComplement(T((result ^ aX) & (result ^ aY))))
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: BinaryComplement(aX) >= aY;
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}
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template<typename T>
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inline bool
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IsSubValid(T aX, T aY)
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{
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// Subtraction is valid if either aX and aY have same sign, or aX-aY and aX
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// have same sign. Since the value of aX-aY is undefined if we have a signed
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// type, we compute it using the unsigned type of the same size.
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typename MakeUnsigned<T>::Type ux = aX;
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typename MakeUnsigned<T>::Type uy = aY;
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typename MakeUnsigned<T>::Type result = ux - uy;
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return IsSigned<T>::value
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? HasSignBit(BinaryComplement(T((result ^ aX) & (aX ^ aY))))
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: aX >= aY;
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}
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template<typename T,
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bool IsTSigned = IsSigned<T>::value,
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bool TwiceBiggerTypeIsSupported =
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IsSupported<typename TwiceBiggerType<T>::Type>::value>
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struct IsMulValidImpl {};
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template<typename T, bool IsTSigned>
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struct IsMulValidImpl<T, IsTSigned, true>
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{
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static bool run(T aX, T aY)
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{
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typedef typename TwiceBiggerType<T>::Type TwiceBiggerType;
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TwiceBiggerType product = TwiceBiggerType(aX) * TwiceBiggerType(aY);
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return IsInRange<T>(product);
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}
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};
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template<typename T>
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struct IsMulValidImpl<T, true, false>
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{
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static bool run(T aX, T aY)
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{
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const T max = MaxValue<T>::value;
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const T min = MinValue<T>::value;
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if (aX == 0 || aY == 0) {
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return true;
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}
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if (aX > 0) {
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return aY > 0
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? aX <= max / aY
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: aY >= min / aX;
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}
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// If we reach this point, we know that aX < 0.
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return aY > 0
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? aX >= min / aY
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: aY >= max / aX;
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}
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};
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template<typename T>
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struct IsMulValidImpl<T, false, false>
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{
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static bool run(T aX, T aY)
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{
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return aY == 0 || aX <= MaxValue<T>::value / aY;
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}
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};
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template<typename T>
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inline bool
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IsMulValid(T aX, T aY)
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{
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return IsMulValidImpl<T>::run(aX, aY);
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}
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template<typename T>
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inline bool
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IsDivValid(T aX, T aY)
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{
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// Keep in mind that in the signed case, min/-1 is invalid because
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// abs(min)>max.
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return aY != 0 &&
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!(IsSigned<T>::value && aX == MinValue<T>::value && aY == T(-1));
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}
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template<typename T, bool IsTSigned = IsSigned<T>::value>
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struct IsModValidImpl;
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template<typename T>
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inline bool
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IsModValid(T aX, T aY)
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{
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return IsModValidImpl<T>::run(aX, aY);
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}
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/*
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* Mod is pretty simple.
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* For now, let's just use the ANSI C definition:
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* If aX or aY are negative, the results are implementation defined.
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* Consider these invalid.
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* Undefined for aY=0.
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* The result will never exceed either aX or aY.
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*
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* Checking that aX>=0 is a warning when T is unsigned.
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*/
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template<typename T>
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struct IsModValidImpl<T, false>
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{
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static inline bool run(T aX, T aY)
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{
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return aY >= 1;
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}
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};
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template<typename T>
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struct IsModValidImpl<T, true>
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{
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static inline bool run(T aX, T aY)
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{
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if (aX < 0) {
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return false;
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}
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return aY >= 1;
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}
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};
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template<typename T, bool IsSigned = IsSigned<T>::value>
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struct NegateImpl;
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template<typename T>
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struct NegateImpl<T, false>
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{
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static CheckedInt<T> negate(const CheckedInt<T>& aVal)
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{
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// Handle negation separately for signed/unsigned, for simpler code and to
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// avoid an MSVC warning negating an unsigned value.
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return CheckedInt<T>(0, aVal.isValid() && aVal.mValue == 0);
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}
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};
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template<typename T>
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struct NegateImpl<T, true>
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{
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static CheckedInt<T> negate(const CheckedInt<T>& aVal)
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{
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// Watch out for the min-value, which (with twos-complement) can't be
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// negated as -min-value is then (max-value + 1).
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if (!aVal.isValid() || aVal.mValue == MinValue<T>::value) {
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return CheckedInt<T>(aVal.mValue, false);
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}
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return CheckedInt<T>(-aVal.mValue, true);
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}
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};
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} // namespace detail
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/*
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* Step 3: Now define the CheckedInt class.
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*/
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/**
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* @class CheckedInt
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* @brief Integer wrapper class checking for integer overflow and other errors
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* @param T the integer type to wrap. Can be any type among the following:
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* - any basic integer type such as |int|
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* - any stdint type such as |int8_t|
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*
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* This class implements guarded integer arithmetic. Do a computation, check
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* that isValid() returns true, you then have a guarantee that no problem, such
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* as integer overflow, happened during this computation, and you can call
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* value() to get the plain integer value.
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*
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* The arithmetic operators in this class are guaranteed not to raise a signal
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* (e.g. in case of a division by zero).
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*
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* For example, suppose that you want to implement a function that computes
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* (aX+aY)/aZ, that doesn't crash if aZ==0, and that reports on error (divide by
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* zero or integer overflow). You could code it as follows:
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@code
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bool computeXPlusYOverZ(int aX, int aY, int aZ, int* aResult)
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{
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CheckedInt<int> checkedResult = (CheckedInt<int>(aX) + aY) / aZ;
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if (checkedResult.isValid()) {
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*aResult = checkedResult.value();
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return true;
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} else {
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return false;
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}
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}
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@endcode
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*
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* Implicit conversion from plain integers to checked integers is allowed. The
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* plain integer is checked to be in range before being casted to the
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* destination type. This means that the following lines all compile, and the
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* resulting CheckedInts are correctly detected as valid or invalid:
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* @code
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// 1 is of type int, is found to be in range for uint8_t, x is valid
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CheckedInt<uint8_t> x(1);
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// -1 is of type int, is found not to be in range for uint8_t, x is invalid
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CheckedInt<uint8_t> x(-1);
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// -1 is of type int, is found to be in range for int8_t, x is valid
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CheckedInt<int8_t> x(-1);
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// 1000 is of type int16_t, is found not to be in range for int8_t,
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// x is invalid
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CheckedInt<int8_t> x(int16_t(1000));
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// 3123456789 is of type uint32_t, is found not to be in range for int32_t,
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// x is invalid
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CheckedInt<int32_t> x(uint32_t(3123456789));
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* @endcode
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* Implicit conversion from
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* checked integers to plain integers is not allowed. As shown in the
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* above example, to get the value of a checked integer as a normal integer,
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* call value().
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*
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* Arithmetic operations between checked and plain integers is allowed; the
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* result type is the type of the checked integer.
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*
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* Checked integers of different types cannot be used in the same arithmetic
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* expression.
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*
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* There are convenience typedefs for all stdint types, of the following form
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* (these are just 2 examples):
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@code
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typedef CheckedInt<int32_t> CheckedInt32;
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typedef CheckedInt<uint16_t> CheckedUint16;
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@endcode
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*/
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template<typename T>
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class CheckedInt
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{
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protected:
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T mValue;
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bool mIsValid;
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template<typename U>
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CheckedInt(U aValue, bool aIsValid) : mValue(aValue), mIsValid(aIsValid)
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{
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static_assert(detail::IsSupported<T>::value &&
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detail::IsSupported<U>::value,
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"This type is not supported by CheckedInt");
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}
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friend struct detail::NegateImpl<T>;
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public:
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/**
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* Constructs a checked integer with given @a value. The checked integer is
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* initialized as valid or invalid depending on whether the @a value
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* is in range.
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*
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* This constructor is not explicit. Instead, the type of its argument is a
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* separate template parameter, ensuring that no conversion is performed
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* before this constructor is actually called. As explained in the above
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* documentation for class CheckedInt, this constructor checks that its
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* argument is valid.
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*/
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template<typename U>
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CheckedInt(U aValue)
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: mValue(T(aValue)),
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mIsValid(detail::IsInRange<T>(aValue))
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{
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static_assert(detail::IsSupported<T>::value &&
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detail::IsSupported<U>::value,
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"This type is not supported by CheckedInt");
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}
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template<typename U>
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friend class CheckedInt;
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template<typename U>
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CheckedInt<U> toChecked() const
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{
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CheckedInt<U> ret(mValue);
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ret.mIsValid = ret.mIsValid && mIsValid;
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return ret;
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}
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/** Constructs a valid checked integer with initial value 0 */
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CheckedInt() : mValue(0), mIsValid(true)
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|
{
|
|
static_assert(detail::IsSupported<T>::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<typename U>
|
|
friend CheckedInt<U> operator +(const CheckedInt<U>& aLhs,
|
|
const CheckedInt<U>& aRhs);
|
|
template<typename U>
|
|
CheckedInt& operator +=(U aRhs);
|
|
|
|
template<typename U>
|
|
friend CheckedInt<U> operator -(const CheckedInt<U>& aLhs,
|
|
const CheckedInt<U>& aRhs);
|
|
template<typename U>
|
|
CheckedInt& operator -=(U aRhs);
|
|
|
|
template<typename U>
|
|
friend CheckedInt<U> operator *(const CheckedInt<U>& aLhs,
|
|
const CheckedInt<U>& aRhs);
|
|
template<typename U>
|
|
CheckedInt& operator *=(U aRhs);
|
|
|
|
template<typename U>
|
|
friend CheckedInt<U> operator /(const CheckedInt<U>& aLhs,
|
|
const CheckedInt<U>& aRhs);
|
|
template<typename U>
|
|
CheckedInt& operator /=(U aRhs);
|
|
|
|
template<typename U>
|
|
friend CheckedInt<U> operator %(const CheckedInt<U>& aLhs,
|
|
const CheckedInt<U>& aRhs);
|
|
template<typename U>
|
|
CheckedInt& operator %=(U aRhs);
|
|
|
|
CheckedInt operator -() const
|
|
{
|
|
return detail::NegateImpl<T>::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<typename U> bool operator !=(U aOther) const MOZ_DELETE;
|
|
template<typename U> bool operator < (U aOther) const MOZ_DELETE;
|
|
template<typename U> bool operator <=(U aOther) const MOZ_DELETE;
|
|
template<typename U> bool operator > (U aOther) const MOZ_DELETE;
|
|
template<typename U> bool operator >=(U aOther) const MOZ_DELETE;
|
|
};
|
|
|
|
#define MOZ_CHECKEDINT_BASIC_BINARY_OPERATOR(NAME, OP) \
|
|
template<typename T> \
|
|
inline CheckedInt<T> \
|
|
operator OP(const CheckedInt<T>& aLhs, const CheckedInt<T>& aRhs) \
|
|
{ \
|
|
if (!detail::Is##NAME##Valid(aLhs.mValue, aRhs.mValue)) { \
|
|
return CheckedInt<T>(0, false); \
|
|
} \
|
|
return CheckedInt<T>(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<T>(x), making sure that
|
|
// - it allows x to be either a CheckedInt<T> or any integer type
|
|
// that can be casted to T
|
|
// - if x is already a CheckedInt<T>, we just return a reference to it,
|
|
// instead of copying it (optimization)
|
|
|
|
namespace detail {
|
|
|
|
template<typename T, typename U>
|
|
struct CastToCheckedIntImpl
|
|
{
|
|
typedef CheckedInt<T> ReturnType;
|
|
static CheckedInt<T> run(U aU) { return aU; }
|
|
};
|
|
|
|
template<typename T>
|
|
struct CastToCheckedIntImpl<T, CheckedInt<T> >
|
|
{
|
|
typedef const CheckedInt<T>& ReturnType;
|
|
static const CheckedInt<T>& run(const CheckedInt<T>& aU) { return aU; }
|
|
};
|
|
|
|
} // namespace detail
|
|
|
|
template<typename T, typename U>
|
|
inline typename detail::CastToCheckedIntImpl<T, U>::ReturnType
|
|
castToCheckedInt(U aU)
|
|
{
|
|
static_assert(detail::IsSupported<T>::value &&
|
|
detail::IsSupported<U>::value,
|
|
"This type is not supported by CheckedInt");
|
|
return detail::CastToCheckedIntImpl<T, U>::run(aU);
|
|
}
|
|
|
|
#define MOZ_CHECKEDINT_CONVENIENCE_BINARY_OPERATORS(OP, COMPOUND_OP) \
|
|
template<typename T> \
|
|
template<typename U> \
|
|
CheckedInt<T>& CheckedInt<T>::operator COMPOUND_OP(U aRhs) \
|
|
{ \
|
|
*this = *this OP castToCheckedInt<T>(aRhs); \
|
|
return *this; \
|
|
} \
|
|
template<typename T, typename U> \
|
|
inline CheckedInt<T> operator OP(const CheckedInt<T>& aLhs, U aRhs) \
|
|
{ \
|
|
return aLhs OP castToCheckedInt<T>(aRhs); \
|
|
} \
|
|
template<typename T, typename U> \
|
|
inline CheckedInt<T> operator OP(U aLhs, const CheckedInt<T>& aRhs) \
|
|
{ \
|
|
return castToCheckedInt<T>(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<typename T, typename U>
|
|
inline bool
|
|
operator ==(const CheckedInt<T>& aLhs, U aRhs)
|
|
{
|
|
return aLhs == castToCheckedInt<T>(aRhs);
|
|
}
|
|
|
|
template<typename T, typename U>
|
|
inline bool
|
|
operator ==(U aLhs, const CheckedInt<T>& aRhs)
|
|
{
|
|
return castToCheckedInt<T>(aLhs) == aRhs;
|
|
}
|
|
|
|
// Convenience typedefs.
|
|
typedef CheckedInt<int8_t> CheckedInt8;
|
|
typedef CheckedInt<uint8_t> CheckedUint8;
|
|
typedef CheckedInt<int16_t> CheckedInt16;
|
|
typedef CheckedInt<uint16_t> CheckedUint16;
|
|
typedef CheckedInt<int32_t> CheckedInt32;
|
|
typedef CheckedInt<uint32_t> CheckedUint32;
|
|
typedef CheckedInt<int64_t> CheckedInt64;
|
|
typedef CheckedInt<uint64_t> CheckedUint64;
|
|
|
|
} // namespace mozilla
|
|
|
|
#endif /* mozilla_CheckedInt_h */
|