394 lines
14 KiB
C++
394 lines
14 KiB
C++
// Copyright 2017 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_NUMERICS_CHECKED_MATH_H_
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#define BASE_NUMERICS_CHECKED_MATH_H_
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#include <stddef.h>
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#include <limits>
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#include <type_traits>
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#include "base/numerics/checked_math_impl.h"
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namespace base {
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namespace internal {
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template <typename T>
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class CheckedNumeric {
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static_assert(std::is_arithmetic<T>::value,
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"CheckedNumeric<T>: T must be a numeric type.");
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public:
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using type = T;
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constexpr CheckedNumeric() = default;
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// Copy constructor.
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template <typename Src>
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constexpr CheckedNumeric(const CheckedNumeric<Src>& rhs)
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: state_(rhs.state_.value(), rhs.IsValid()) {}
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template <typename Src>
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friend class CheckedNumeric;
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// This is not an explicit constructor because we implicitly upgrade regular
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// numerics to CheckedNumerics to make them easier to use.
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template <typename Src>
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constexpr CheckedNumeric(Src value) // NOLINT(runtime/explicit)
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: state_(value) {
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static_assert(std::is_arithmetic<Src>::value, "Argument must be numeric.");
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}
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// This is not an explicit constructor because we want a seamless conversion
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// from StrictNumeric types.
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template <typename Src>
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constexpr CheckedNumeric(
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StrictNumeric<Src> value) // NOLINT(runtime/explicit)
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: state_(static_cast<Src>(value)) {}
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// IsValid() - The public API to test if a CheckedNumeric is currently valid.
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// A range checked destination type can be supplied using the Dst template
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// parameter.
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template <typename Dst = T>
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constexpr bool IsValid() const {
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return state_.is_valid() &&
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IsValueInRangeForNumericType<Dst>(state_.value());
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}
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// AssignIfValid(Dst) - Assigns the underlying value if it is currently valid
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// and is within the range supported by the destination type. Returns true if
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// successful and false otherwise.
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template <typename Dst>
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#if defined(__clang__) || defined(__GNUC__)
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__attribute__((warn_unused_result))
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#elif defined(_MSC_VER)
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_Check_return_
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#endif
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constexpr bool
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AssignIfValid(Dst* result) const {
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return BASE_NUMERICS_LIKELY(IsValid<Dst>())
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? ((*result = static_cast<Dst>(state_.value())), true)
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: false;
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}
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// ValueOrDie() - The primary accessor for the underlying value. If the
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// current state is not valid it will CHECK and crash.
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// A range checked destination type can be supplied using the Dst template
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// parameter, which will trigger a CHECK if the value is not in bounds for
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// the destination.
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// The CHECK behavior can be overridden by supplying a handler as a
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// template parameter, for test code, etc. However, the handler cannot access
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// the underlying value, and it is not available through other means.
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template <typename Dst = T, class CheckHandler = CheckOnFailure>
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constexpr StrictNumeric<Dst> ValueOrDie() const {
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return BASE_NUMERICS_LIKELY(IsValid<Dst>())
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? static_cast<Dst>(state_.value())
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: CheckHandler::template HandleFailure<Dst>();
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}
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// ValueOrDefault(T default_value) - A convenience method that returns the
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// current value if the state is valid, and the supplied default_value for
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// any other state.
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// A range checked destination type can be supplied using the Dst template
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// parameter. WARNING: This function may fail to compile or CHECK at runtime
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// if the supplied default_value is not within range of the destination type.
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template <typename Dst = T, typename Src>
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constexpr StrictNumeric<Dst> ValueOrDefault(const Src default_value) const {
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return BASE_NUMERICS_LIKELY(IsValid<Dst>())
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? static_cast<Dst>(state_.value())
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: checked_cast<Dst>(default_value);
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}
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// Returns a checked numeric of the specified type, cast from the current
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// CheckedNumeric. If the current state is invalid or the destination cannot
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// represent the result then the returned CheckedNumeric will be invalid.
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template <typename Dst>
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constexpr CheckedNumeric<typename UnderlyingType<Dst>::type> Cast() const {
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return *this;
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}
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// This friend method is available solely for providing more detailed logging
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// in the the tests. Do not implement it in production code, because the
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// underlying values may change at any time.
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template <typename U>
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friend U GetNumericValueForTest(const CheckedNumeric<U>& src);
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// Prototypes for the supported arithmetic operator overloads.
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template <typename Src>
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constexpr CheckedNumeric& operator+=(const Src rhs);
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template <typename Src>
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constexpr CheckedNumeric& operator-=(const Src rhs);
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template <typename Src>
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constexpr CheckedNumeric& operator*=(const Src rhs);
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template <typename Src>
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constexpr CheckedNumeric& operator/=(const Src rhs);
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template <typename Src>
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constexpr CheckedNumeric& operator%=(const Src rhs);
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template <typename Src>
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constexpr CheckedNumeric& operator<<=(const Src rhs);
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template <typename Src>
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constexpr CheckedNumeric& operator>>=(const Src rhs);
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template <typename Src>
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constexpr CheckedNumeric& operator&=(const Src rhs);
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template <typename Src>
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constexpr CheckedNumeric& operator|=(const Src rhs);
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template <typename Src>
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constexpr CheckedNumeric& operator^=(const Src rhs);
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constexpr CheckedNumeric operator-() const {
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// The negation of two's complement int min is int min, so we simply
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// check for that in the constexpr case.
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// We use an optimized code path for a known run-time variable.
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return MustTreatAsConstexpr(state_.value()) || !std::is_signed<T>::value ||
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std::is_floating_point<T>::value
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? CheckedNumeric<T>(
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NegateWrapper(state_.value()),
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IsValid() && (!std::is_signed<T>::value ||
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std::is_floating_point<T>::value ||
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NegateWrapper(state_.value()) !=
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std::numeric_limits<T>::lowest()))
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: FastRuntimeNegate();
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}
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constexpr CheckedNumeric operator~() const {
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return CheckedNumeric<decltype(InvertWrapper(T()))>(
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InvertWrapper(state_.value()), IsValid());
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}
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constexpr CheckedNumeric Abs() const {
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return !IsValueNegative(state_.value()) ? *this : -*this;
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}
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template <typename U>
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constexpr CheckedNumeric<typename MathWrapper<CheckedMaxOp, T, U>::type> Max(
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const U rhs) const {
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using R = typename UnderlyingType<U>::type;
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using result_type = typename MathWrapper<CheckedMaxOp, T, U>::type;
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// TODO(jschuh): This can be converted to the MathOp version and remain
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// constexpr once we have C++14 support.
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return CheckedNumeric<result_type>(
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static_cast<result_type>(
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IsGreater<T, R>::Test(state_.value(), Wrapper<U>::value(rhs))
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? state_.value()
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: Wrapper<U>::value(rhs)),
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state_.is_valid() && Wrapper<U>::is_valid(rhs));
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}
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template <typename U>
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constexpr CheckedNumeric<typename MathWrapper<CheckedMinOp, T, U>::type> Min(
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const U rhs) const {
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using R = typename UnderlyingType<U>::type;
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using result_type = typename MathWrapper<CheckedMinOp, T, U>::type;
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// TODO(jschuh): This can be converted to the MathOp version and remain
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// constexpr once we have C++14 support.
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return CheckedNumeric<result_type>(
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static_cast<result_type>(
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IsLess<T, R>::Test(state_.value(), Wrapper<U>::value(rhs))
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? state_.value()
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: Wrapper<U>::value(rhs)),
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state_.is_valid() && Wrapper<U>::is_valid(rhs));
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}
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// This function is available only for integral types. It returns an unsigned
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// integer of the same width as the source type, containing the absolute value
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// of the source, and properly handling signed min.
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constexpr CheckedNumeric<typename UnsignedOrFloatForSize<T>::type>
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UnsignedAbs() const {
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return CheckedNumeric<typename UnsignedOrFloatForSize<T>::type>(
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SafeUnsignedAbs(state_.value()), state_.is_valid());
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}
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constexpr CheckedNumeric& operator++() {
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*this += 1;
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return *this;
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}
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constexpr CheckedNumeric operator++(int) {
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CheckedNumeric value = *this;
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*this += 1;
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return value;
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}
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constexpr CheckedNumeric& operator--() {
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*this -= 1;
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return *this;
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}
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constexpr CheckedNumeric operator--(int) {
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CheckedNumeric value = *this;
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*this -= 1;
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return value;
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}
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// These perform the actual math operations on the CheckedNumerics.
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// Binary arithmetic operations.
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template <template <typename, typename, typename> class M,
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typename L,
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typename R>
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static constexpr CheckedNumeric MathOp(const L lhs, const R rhs) {
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using Math = typename MathWrapper<M, L, R>::math;
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T result = 0;
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bool is_valid =
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Wrapper<L>::is_valid(lhs) && Wrapper<R>::is_valid(rhs) &&
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Math::Do(Wrapper<L>::value(lhs), Wrapper<R>::value(rhs), &result);
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return CheckedNumeric<T>(result, is_valid);
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}
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// Assignment arithmetic operations.
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template <template <typename, typename, typename> class M, typename R>
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constexpr CheckedNumeric& MathOp(const R rhs) {
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using Math = typename MathWrapper<M, T, R>::math;
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T result = 0; // Using T as the destination saves a range check.
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bool is_valid = state_.is_valid() && Wrapper<R>::is_valid(rhs) &&
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Math::Do(state_.value(), Wrapper<R>::value(rhs), &result);
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*this = CheckedNumeric<T>(result, is_valid);
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return *this;
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}
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private:
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CheckedNumericState<T> state_;
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CheckedNumeric FastRuntimeNegate() const {
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T result;
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bool success = CheckedSubOp<T, T>::Do(T(0), state_.value(), &result);
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return CheckedNumeric<T>(result, IsValid() && success);
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}
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template <typename Src>
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constexpr CheckedNumeric(Src value, bool is_valid)
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: state_(value, is_valid) {}
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// These wrappers allow us to handle state the same way for both
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// CheckedNumeric and POD arithmetic types.
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template <typename Src>
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struct Wrapper {
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static constexpr bool is_valid(Src) { return true; }
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static constexpr Src value(Src value) { return value; }
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};
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template <typename Src>
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struct Wrapper<CheckedNumeric<Src>> {
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static constexpr bool is_valid(const CheckedNumeric<Src> v) {
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return v.IsValid();
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}
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static constexpr Src value(const CheckedNumeric<Src> v) {
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return v.state_.value();
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}
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};
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template <typename Src>
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struct Wrapper<StrictNumeric<Src>> {
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static constexpr bool is_valid(const StrictNumeric<Src>) { return true; }
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static constexpr Src value(const StrictNumeric<Src> v) {
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return static_cast<Src>(v);
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}
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};
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};
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// Convenience functions to avoid the ugly template disambiguator syntax.
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template <typename Dst, typename Src>
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constexpr bool IsValidForType(const CheckedNumeric<Src> value) {
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return value.template IsValid<Dst>();
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}
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template <typename Dst, typename Src>
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constexpr StrictNumeric<Dst> ValueOrDieForType(
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const CheckedNumeric<Src> value) {
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return value.template ValueOrDie<Dst>();
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}
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template <typename Dst, typename Src, typename Default>
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constexpr StrictNumeric<Dst> ValueOrDefaultForType(
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const CheckedNumeric<Src> value,
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const Default default_value) {
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return value.template ValueOrDefault<Dst>(default_value);
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}
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// Convience wrapper to return a new CheckedNumeric from the provided arithmetic
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// or CheckedNumericType.
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template <typename T>
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constexpr CheckedNumeric<typename UnderlyingType<T>::type> MakeCheckedNum(
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const T value) {
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return value;
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}
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// These implement the variadic wrapper for the math operations.
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template <template <typename, typename, typename> class M,
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typename L,
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typename R>
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constexpr CheckedNumeric<typename MathWrapper<M, L, R>::type> CheckMathOp(
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const L lhs,
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const R rhs) {
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using Math = typename MathWrapper<M, L, R>::math;
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return CheckedNumeric<typename Math::result_type>::template MathOp<M>(lhs,
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rhs);
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}
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// General purpose wrapper template for arithmetic operations.
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template <template <typename, typename, typename> class M,
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typename L,
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typename R,
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typename... Args>
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constexpr CheckedNumeric<typename ResultType<M, L, R, Args...>::type>
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CheckMathOp(const L lhs, const R rhs, const Args... args) {
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return CheckMathOp<M>(CheckMathOp<M>(lhs, rhs), args...);
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}
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Add, +, +=)
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Sub, -, -=)
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Mul, *, *=)
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Div, /, /=)
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Mod, %, %=)
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Lsh, <<, <<=)
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Rsh, >>, >>=)
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, And, &, &=)
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Or, |, |=)
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BASE_NUMERIC_ARITHMETIC_OPERATORS(Checked, Check, Xor, ^, ^=)
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BASE_NUMERIC_ARITHMETIC_VARIADIC(Checked, Check, Max)
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BASE_NUMERIC_ARITHMETIC_VARIADIC(Checked, Check, Min)
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// These are some extra StrictNumeric operators to support simple pointer
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// arithmetic with our result types. Since wrapping on a pointer is always
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// bad, we trigger the CHECK condition here.
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template <typename L, typename R>
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L* operator+(L* lhs, const StrictNumeric<R> rhs) {
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uintptr_t result = CheckAdd(reinterpret_cast<uintptr_t>(lhs),
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CheckMul(sizeof(L), static_cast<R>(rhs)))
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.template ValueOrDie<uintptr_t>();
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return reinterpret_cast<L*>(result);
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}
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template <typename L, typename R>
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L* operator-(L* lhs, const StrictNumeric<R> rhs) {
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uintptr_t result = CheckSub(reinterpret_cast<uintptr_t>(lhs),
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CheckMul(sizeof(L), static_cast<R>(rhs)))
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.template ValueOrDie<uintptr_t>();
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return reinterpret_cast<L*>(result);
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}
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} // namespace internal
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using internal::CheckedNumeric;
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using internal::IsValidForType;
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using internal::ValueOrDieForType;
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using internal::ValueOrDefaultForType;
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using internal::MakeCheckedNum;
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using internal::CheckMax;
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using internal::CheckMin;
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using internal::CheckAdd;
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using internal::CheckSub;
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using internal::CheckMul;
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using internal::CheckDiv;
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using internal::CheckMod;
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using internal::CheckLsh;
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using internal::CheckRsh;
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using internal::CheckAnd;
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using internal::CheckOr;
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using internal::CheckXor;
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} // namespace base
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#endif // BASE_NUMERICS_CHECKED_MATH_H_
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