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Diffstat (limited to 'security/sandbox/chromium/base/numerics/safe_conversions.h')
| -rw-r--r-- | security/sandbox/chromium/base/numerics/safe_conversions.h | 358 |
1 files changed, 358 insertions, 0 deletions
diff --git a/security/sandbox/chromium/base/numerics/safe_conversions.h b/security/sandbox/chromium/base/numerics/safe_conversions.h new file mode 100644 index 0000000000..b9636fec42 --- /dev/null +++ b/security/sandbox/chromium/base/numerics/safe_conversions.h @@ -0,0 +1,358 @@ +// Copyright 2014 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#ifndef BASE_NUMERICS_SAFE_CONVERSIONS_H_ +#define BASE_NUMERICS_SAFE_CONVERSIONS_H_ + +#include <stddef.h> + +#include <limits> +#include <type_traits> + +#include "base/numerics/safe_conversions_impl.h" + +#if !defined(__native_client__) && (defined(__ARMEL__) || defined(__arch64__)) +#include "base/numerics/safe_conversions_arm_impl.h" +#define BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS (1) +#else +#define BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS (0) +#endif + +#if !BASE_NUMERICS_DISABLE_OSTREAM_OPERATORS +#include <ostream> +#endif + +namespace base { +namespace internal { + +#if !BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS +template <typename Dst, typename Src> +struct SaturateFastAsmOp { + static const bool is_supported = false; + static constexpr Dst Do(Src) { + // Force a compile failure if instantiated. + return CheckOnFailure::template HandleFailure<Dst>(); + } +}; +#endif // BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS +#undef BASE_HAS_OPTIMIZED_SAFE_CONVERSIONS + +// The following special case a few specific integer conversions where we can +// eke out better performance than range checking. +template <typename Dst, typename Src, typename Enable = void> +struct IsValueInRangeFastOp { + static const bool is_supported = false; + static constexpr bool Do(Src value) { + // Force a compile failure if instantiated. + return CheckOnFailure::template HandleFailure<bool>(); + } +}; + +// Signed to signed range comparison. +template <typename Dst, typename Src> +struct IsValueInRangeFastOp< + Dst, + Src, + typename std::enable_if< + std::is_integral<Dst>::value && std::is_integral<Src>::value && + std::is_signed<Dst>::value && std::is_signed<Src>::value && + !IsTypeInRangeForNumericType<Dst, Src>::value>::type> { + static const bool is_supported = true; + + static constexpr bool Do(Src value) { + // Just downcast to the smaller type, sign extend it back to the original + // type, and then see if it matches the original value. + return value == static_cast<Dst>(value); + } +}; + +// Signed to unsigned range comparison. +template <typename Dst, typename Src> +struct IsValueInRangeFastOp< + Dst, + Src, + typename std::enable_if< + std::is_integral<Dst>::value && std::is_integral<Src>::value && + !std::is_signed<Dst>::value && std::is_signed<Src>::value && + !IsTypeInRangeForNumericType<Dst, Src>::value>::type> { + static const bool is_supported = true; + + static constexpr bool Do(Src value) { + // We cast a signed as unsigned to overflow negative values to the top, + // then compare against whichever maximum is smaller, as our upper bound. + return as_unsigned(value) <= as_unsigned(CommonMax<Src, Dst>()); + } +}; + +// Convenience function that returns true if the supplied value is in range +// for the destination type. +template <typename Dst, typename Src> +constexpr bool IsValueInRangeForNumericType(Src value) { + using SrcType = typename internal::UnderlyingType<Src>::type; + return internal::IsValueInRangeFastOp<Dst, SrcType>::is_supported + ? internal::IsValueInRangeFastOp<Dst, SrcType>::Do( + static_cast<SrcType>(value)) + : internal::DstRangeRelationToSrcRange<Dst>( + static_cast<SrcType>(value)) + .IsValid(); +} + +// checked_cast<> is analogous to static_cast<> for numeric types, +// except that it CHECKs that the specified numeric conversion will not +// overflow or underflow. NaN source will always trigger a CHECK. +template <typename Dst, + class CheckHandler = internal::CheckOnFailure, + typename Src> +constexpr Dst checked_cast(Src value) { + // This throws a compile-time error on evaluating the constexpr if it can be + // determined at compile-time as failing, otherwise it will CHECK at runtime. + using SrcType = typename internal::UnderlyingType<Src>::type; + return BASE_NUMERICS_LIKELY((IsValueInRangeForNumericType<Dst>(value))) + ? static_cast<Dst>(static_cast<SrcType>(value)) + : CheckHandler::template HandleFailure<Dst>(); +} + +// Default boundaries for integral/float: max/infinity, lowest/-infinity, 0/NaN. +// You may provide your own limits (e.g. to saturated_cast) so long as you +// implement all of the static constexpr member functions in the class below. +template <typename T> +struct SaturationDefaultLimits : public std::numeric_limits<T> { + static constexpr T NaN() { + return std::numeric_limits<T>::has_quiet_NaN + ? std::numeric_limits<T>::quiet_NaN() + : T(); + } + using std::numeric_limits<T>::max; + static constexpr T Overflow() { + return std::numeric_limits<T>::has_infinity + ? std::numeric_limits<T>::infinity() + : std::numeric_limits<T>::max(); + } + using std::numeric_limits<T>::lowest; + static constexpr T Underflow() { + return std::numeric_limits<T>::has_infinity + ? std::numeric_limits<T>::infinity() * -1 + : std::numeric_limits<T>::lowest(); + } +}; + +template <typename Dst, template <typename> class S, typename Src> +constexpr Dst saturated_cast_impl(Src value, RangeCheck constraint) { + // For some reason clang generates much better code when the branch is + // structured exactly this way, rather than a sequence of checks. + return !constraint.IsOverflowFlagSet() + ? (!constraint.IsUnderflowFlagSet() ? static_cast<Dst>(value) + : S<Dst>::Underflow()) + // Skip this check for integral Src, which cannot be NaN. + : (std::is_integral<Src>::value || !constraint.IsUnderflowFlagSet() + ? S<Dst>::Overflow() + : S<Dst>::NaN()); +} + +// We can reduce the number of conditions and get slightly better performance +// for normal signed and unsigned integer ranges. And in the specific case of +// Arm, we can use the optimized saturation instructions. +template <typename Dst, typename Src, typename Enable = void> +struct SaturateFastOp { + static const bool is_supported = false; + static constexpr Dst Do(Src value) { + // Force a compile failure if instantiated. + return CheckOnFailure::template HandleFailure<Dst>(); + } +}; + +template <typename Dst, typename Src> +struct SaturateFastOp< + Dst, + Src, + typename std::enable_if<std::is_integral<Src>::value && + std::is_integral<Dst>::value && + SaturateFastAsmOp<Dst, Src>::is_supported>::type> { + static const bool is_supported = true; + static Dst Do(Src value) { return SaturateFastAsmOp<Dst, Src>::Do(value); } +}; + +template <typename Dst, typename Src> +struct SaturateFastOp< + Dst, + Src, + typename std::enable_if<std::is_integral<Src>::value && + std::is_integral<Dst>::value && + !SaturateFastAsmOp<Dst, Src>::is_supported>::type> { + static const bool is_supported = true; + static Dst Do(Src value) { + // The exact order of the following is structured to hit the correct + // optimization heuristics across compilers. Do not change without + // checking the emitted code. + Dst saturated = CommonMaxOrMin<Dst, Src>( + IsMaxInRangeForNumericType<Dst, Src>() || + (!IsMinInRangeForNumericType<Dst, Src>() && IsValueNegative(value))); + return BASE_NUMERICS_LIKELY(IsValueInRangeForNumericType<Dst>(value)) + ? static_cast<Dst>(value) + : saturated; + } +}; + +// saturated_cast<> is analogous to static_cast<> for numeric types, except +// that the specified numeric conversion will saturate by default rather than +// overflow or underflow, and NaN assignment to an integral will return 0. +// All boundary condition behaviors can be overriden with a custom handler. +template <typename Dst, + template <typename> class SaturationHandler = SaturationDefaultLimits, + typename Src> +constexpr Dst saturated_cast(Src value) { + using SrcType = typename UnderlyingType<Src>::type; + return !IsCompileTimeConstant(value) && + SaturateFastOp<Dst, SrcType>::is_supported && + std::is_same<SaturationHandler<Dst>, + SaturationDefaultLimits<Dst>>::value + ? SaturateFastOp<Dst, SrcType>::Do(static_cast<SrcType>(value)) + : saturated_cast_impl<Dst, SaturationHandler, SrcType>( + static_cast<SrcType>(value), + DstRangeRelationToSrcRange<Dst, SaturationHandler, SrcType>( + static_cast<SrcType>(value))); +} + +// strict_cast<> is analogous to static_cast<> for numeric types, except that +// it will cause a compile failure if the destination type is not large enough +// to contain any value in the source type. It performs no runtime checking. +template <typename Dst, typename Src> +constexpr Dst strict_cast(Src value) { + using SrcType = typename UnderlyingType<Src>::type; + static_assert(UnderlyingType<Src>::is_numeric, "Argument must be numeric."); + static_assert(std::is_arithmetic<Dst>::value, "Result must be numeric."); + + // If you got here from a compiler error, it's because you tried to assign + // from a source type to a destination type that has insufficient range. + // The solution may be to change the destination type you're assigning to, + // and use one large enough to represent the source. + // Alternatively, you may be better served with the checked_cast<> or + // saturated_cast<> template functions for your particular use case. + static_assert(StaticDstRangeRelationToSrcRange<Dst, SrcType>::value == + NUMERIC_RANGE_CONTAINED, + "The source type is out of range for the destination type. " + "Please see strict_cast<> comments for more information."); + + return static_cast<Dst>(static_cast<SrcType>(value)); +} + +// Some wrappers to statically check that a type is in range. +template <typename Dst, typename Src, class Enable = void> +struct IsNumericRangeContained { + static const bool value = false; +}; + +template <typename Dst, typename Src> +struct IsNumericRangeContained< + Dst, + Src, + typename std::enable_if<ArithmeticOrUnderlyingEnum<Dst>::value && + ArithmeticOrUnderlyingEnum<Src>::value>::type> { + static const bool value = StaticDstRangeRelationToSrcRange<Dst, Src>::value == + NUMERIC_RANGE_CONTAINED; +}; + +// StrictNumeric implements compile time range checking between numeric types by +// wrapping assignment operations in a strict_cast. This class is intended to be +// used for function arguments and return types, to ensure the destination type +// can always contain the source type. This is essentially the same as enforcing +// -Wconversion in gcc and C4302 warnings on MSVC, but it can be applied +// incrementally at API boundaries, making it easier to convert code so that it +// compiles cleanly with truncation warnings enabled. +// This template should introduce no runtime overhead, but it also provides no +// runtime checking of any of the associated mathematical operations. Use +// CheckedNumeric for runtime range checks of the actual value being assigned. +template <typename T> +class StrictNumeric { + public: + using type = T; + + constexpr StrictNumeric() : value_(0) {} + + // Copy constructor. + template <typename Src> + constexpr StrictNumeric(const StrictNumeric<Src>& rhs) + : value_(strict_cast<T>(rhs.value_)) {} + + // This is not an explicit constructor because we implicitly upgrade regular + // numerics to StrictNumerics to make them easier to use. + template <typename Src> + constexpr StrictNumeric(Src value) // NOLINT(runtime/explicit) + : value_(strict_cast<T>(value)) {} + + // If you got here from a compiler error, it's because you tried to assign + // from a source type to a destination type that has insufficient range. + // The solution may be to change the destination type you're assigning to, + // and use one large enough to represent the source. + // If you're assigning from a CheckedNumeric<> class, you may be able to use + // the AssignIfValid() member function, specify a narrower destination type to + // the member value functions (e.g. val.template ValueOrDie<Dst>()), use one + // of the value helper functions (e.g. ValueOrDieForType<Dst>(val)). + // If you've encountered an _ambiguous overload_ you can use a static_cast<> + // to explicitly cast the result to the destination type. + // If none of that works, you may be better served with the checked_cast<> or + // saturated_cast<> template functions for your particular use case. + template <typename Dst, + typename std::enable_if< + IsNumericRangeContained<Dst, T>::value>::type* = nullptr> + constexpr operator Dst() const { + return static_cast<typename ArithmeticOrUnderlyingEnum<Dst>::type>(value_); + } + + private: + const T value_; +}; + +// Convience wrapper returns a StrictNumeric from the provided arithmetic type. +template <typename T> +constexpr StrictNumeric<typename UnderlyingType<T>::type> MakeStrictNum( + const T value) { + return value; +} + +#if !BASE_NUMERICS_DISABLE_OSTREAM_OPERATORS +// Overload the ostream output operator to make logging work nicely. +template <typename T> +std::ostream& operator<<(std::ostream& os, const StrictNumeric<T>& value) { + os << static_cast<T>(value); + return os; +} +#endif + +#define BASE_NUMERIC_COMPARISON_OPERATORS(CLASS, NAME, OP) \ + template <typename L, typename R, \ + typename std::enable_if< \ + internal::Is##CLASS##Op<L, R>::value>::type* = nullptr> \ + constexpr bool operator OP(const L lhs, const R rhs) { \ + return SafeCompare<NAME, typename UnderlyingType<L>::type, \ + typename UnderlyingType<R>::type>(lhs, rhs); \ + } + +BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsLess, <) +BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsLessOrEqual, <=) +BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsGreater, >) +BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsGreaterOrEqual, >=) +BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsEqual, ==) +BASE_NUMERIC_COMPARISON_OPERATORS(Strict, IsNotEqual, !=) + +} // namespace internal + +using internal::as_signed; +using internal::as_unsigned; +using internal::checked_cast; +using internal::strict_cast; +using internal::saturated_cast; +using internal::SafeUnsignedAbs; +using internal::StrictNumeric; +using internal::MakeStrictNum; +using internal::IsValueInRangeForNumericType; +using internal::IsTypeInRangeForNumericType; +using internal::IsValueNegative; + +// Explicitly make a shorter size_t alias for convenience. +using SizeT = StrictNumeric<size_t>; + +} // namespace base + +#endif // BASE_NUMERICS_SAFE_CONVERSIONS_H_ |