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Diffstat (limited to 'third_party/numerics/safe_conversions_impl.h')
| -rw-r--r-- | third_party/numerics/safe_conversions_impl.h | 217 |
1 files changed, 217 insertions, 0 deletions
diff --git a/third_party/numerics/safe_conversions_impl.h b/third_party/numerics/safe_conversions_impl.h new file mode 100644 index 0000000000..a357e518d1 --- /dev/null +++ b/third_party/numerics/safe_conversions_impl.h @@ -0,0 +1,217 @@ +// 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_SAFE_CONVERSIONS_IMPL_H_ +#define BASE_SAFE_CONVERSIONS_IMPL_H_ + +#include <limits> + +#include "../macros.h" +#include "../template_util.h" + +namespace base { +namespace internal { + +// The std library doesn't provide a binary max_exponent for integers, however +// we can compute one by adding one to the number of non-sign bits. This allows +// for accurate range comparisons between floating point and integer types. +template <typename NumericType> +struct MaxExponent { + static const int value = std::numeric_limits<NumericType>::is_iec559 + ? std::numeric_limits<NumericType>::max_exponent + : (sizeof(NumericType) * 8 + 1 - + std::numeric_limits<NumericType>::is_signed); +}; + +enum IntegerRepresentation { + INTEGER_REPRESENTATION_UNSIGNED, + INTEGER_REPRESENTATION_SIGNED +}; + +// A range for a given nunmeric Src type is contained for a given numeric Dst +// type if both numeric_limits<Src>::max() <= numeric_limits<Dst>::max() and +// numeric_limits<Src>::min() >= numeric_limits<Dst>::min() are true. +// We implement this as template specializations rather than simple static +// comparisons to ensure type correctness in our comparisons. +enum NumericRangeRepresentation { + NUMERIC_RANGE_NOT_CONTAINED, + NUMERIC_RANGE_CONTAINED +}; + +// Helper templates to statically determine if our destination type can contain +// maximum and minimum values represented by the source type. + +template < + typename Dst, + typename Src, + IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed + ? INTEGER_REPRESENTATION_SIGNED + : INTEGER_REPRESENTATION_UNSIGNED, + IntegerRepresentation SrcSign = + std::numeric_limits<Src>::is_signed + ? INTEGER_REPRESENTATION_SIGNED + : INTEGER_REPRESENTATION_UNSIGNED > +struct StaticDstRangeRelationToSrcRange; + +// Same sign: Dst is guaranteed to contain Src only if its range is equal or +// larger. +template <typename Dst, typename Src, IntegerRepresentation Sign> +struct StaticDstRangeRelationToSrcRange<Dst, Src, Sign, Sign> { + static const NumericRangeRepresentation value = + MaxExponent<Dst>::value >= MaxExponent<Src>::value + ? NUMERIC_RANGE_CONTAINED + : NUMERIC_RANGE_NOT_CONTAINED; +}; + +// Unsigned to signed: Dst is guaranteed to contain source only if its range is +// larger. +template <typename Dst, typename Src> +struct StaticDstRangeRelationToSrcRange<Dst, + Src, + INTEGER_REPRESENTATION_SIGNED, + INTEGER_REPRESENTATION_UNSIGNED> { + static const NumericRangeRepresentation value = + MaxExponent<Dst>::value > MaxExponent<Src>::value + ? NUMERIC_RANGE_CONTAINED + : NUMERIC_RANGE_NOT_CONTAINED; +}; + +// Signed to unsigned: Dst cannot be statically determined to contain Src. +template <typename Dst, typename Src> +struct StaticDstRangeRelationToSrcRange<Dst, + Src, + INTEGER_REPRESENTATION_UNSIGNED, + INTEGER_REPRESENTATION_SIGNED> { + static const NumericRangeRepresentation value = NUMERIC_RANGE_NOT_CONTAINED; +}; + +enum RangeConstraint { + RANGE_VALID = 0x0, // Value can be represented by the destination type. + RANGE_UNDERFLOW = 0x1, // Value would overflow. + RANGE_OVERFLOW = 0x2, // Value would underflow. + RANGE_INVALID = RANGE_UNDERFLOW | RANGE_OVERFLOW // Invalid (i.e. NaN). +}; + +// Helper function for coercing an int back to a RangeContraint. +inline RangeConstraint GetRangeConstraint(int integer_range_constraint) { + assert(integer_range_constraint >= RANGE_VALID && + integer_range_constraint <= RANGE_INVALID); + return static_cast<RangeConstraint>(integer_range_constraint); +} + +// This function creates a RangeConstraint from an upper and lower bound +// check by taking advantage of the fact that only NaN can be out of range in +// both directions at once. +inline RangeConstraint GetRangeConstraint(bool is_in_upper_bound, + bool is_in_lower_bound) { + return GetRangeConstraint((is_in_upper_bound ? 0 : RANGE_OVERFLOW) | + (is_in_lower_bound ? 0 : RANGE_UNDERFLOW)); +} + +template < + typename Dst, + typename Src, + IntegerRepresentation DstSign = std::numeric_limits<Dst>::is_signed + ? INTEGER_REPRESENTATION_SIGNED + : INTEGER_REPRESENTATION_UNSIGNED, + IntegerRepresentation SrcSign = std::numeric_limits<Src>::is_signed + ? INTEGER_REPRESENTATION_SIGNED + : INTEGER_REPRESENTATION_UNSIGNED, + NumericRangeRepresentation DstRange = + StaticDstRangeRelationToSrcRange<Dst, Src>::value > +struct DstRangeRelationToSrcRangeImpl; + +// The following templates are for ranges that must be verified at runtime. We +// split it into checks based on signedness to avoid confusing casts and +// compiler warnings on signed an unsigned comparisons. + +// Dst range is statically determined to contain Src: Nothing to check. +template <typename Dst, + typename Src, + IntegerRepresentation DstSign, + IntegerRepresentation SrcSign> +struct DstRangeRelationToSrcRangeImpl<Dst, + Src, + DstSign, + SrcSign, + NUMERIC_RANGE_CONTAINED> { + static RangeConstraint Check(Src value) { return RANGE_VALID; } +}; + +// Signed to signed narrowing: Both the upper and lower boundaries may be +// exceeded. +template <typename Dst, typename Src> +struct DstRangeRelationToSrcRangeImpl<Dst, + Src, + INTEGER_REPRESENTATION_SIGNED, + INTEGER_REPRESENTATION_SIGNED, + NUMERIC_RANGE_NOT_CONTAINED> { + static RangeConstraint Check(Src value) { + return std::numeric_limits<Dst>::is_iec559 + ? GetRangeConstraint(value <= std::numeric_limits<Dst>::max(), + value >= -std::numeric_limits<Dst>::max()) + : GetRangeConstraint(value <= std::numeric_limits<Dst>::max(), + value >= std::numeric_limits<Dst>::min()); + } +}; + +// Unsigned to unsigned narrowing: Only the upper boundary can be exceeded. +template <typename Dst, typename Src> +struct DstRangeRelationToSrcRangeImpl<Dst, + Src, + INTEGER_REPRESENTATION_UNSIGNED, + INTEGER_REPRESENTATION_UNSIGNED, + NUMERIC_RANGE_NOT_CONTAINED> { + static RangeConstraint Check(Src value) { + return GetRangeConstraint(value <= std::numeric_limits<Dst>::max(), true); + } +}; + +// Unsigned to signed: The upper boundary may be exceeded. +template <typename Dst, typename Src> +struct DstRangeRelationToSrcRangeImpl<Dst, + Src, + INTEGER_REPRESENTATION_SIGNED, + INTEGER_REPRESENTATION_UNSIGNED, + NUMERIC_RANGE_NOT_CONTAINED> { + static RangeConstraint Check(Src value) { + return sizeof(Dst) > sizeof(Src) + ? RANGE_VALID + : GetRangeConstraint( + value <= static_cast<Src>(std::numeric_limits<Dst>::max()), + true); + } +}; + +// Signed to unsigned: The upper boundary may be exceeded for a narrower Dst, +// and any negative value exceeds the lower boundary. +template <typename Dst, typename Src> +struct DstRangeRelationToSrcRangeImpl<Dst, + Src, + INTEGER_REPRESENTATION_UNSIGNED, + INTEGER_REPRESENTATION_SIGNED, + NUMERIC_RANGE_NOT_CONTAINED> { + static RangeConstraint Check(Src value) { + return (MaxExponent<Dst>::value >= MaxExponent<Src>::value) + ? GetRangeConstraint(true, value >= static_cast<Src>(0)) + : GetRangeConstraint( + value <= static_cast<Src>(std::numeric_limits<Dst>::max()), + value >= static_cast<Src>(0)); + } +}; + +template <typename Dst, typename Src> +inline RangeConstraint DstRangeRelationToSrcRange(Src value) { + COMPILE_ASSERT(std::numeric_limits<Src>::is_specialized, + argument_must_be_numeric); + COMPILE_ASSERT(std::numeric_limits<Dst>::is_specialized, + result_must_be_numeric); + return DstRangeRelationToSrcRangeImpl<Dst, Src>::Check(value); +} + +} // namespace internal +} // namespace base + +#endif // BASE_SAFE_CONVERSIONS_IMPL_H_ + |