// 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_MATH_H_
#define BASE_SAFE_MATH_H_
#include "base/numerics/safe_math_impl.h"
namespace base {
namespace internal {
// CheckedNumeric implements all the logic and operators for detecting integer
// boundary conditions such as overflow, underflow, and invalid conversions.
// The CheckedNumeric type implicitly converts from floating point and integer
// data types, and contains overloads for basic arithmetic operations (i.e.: +,
// -, *, /, %).
//
// The following methods convert from CheckedNumeric to standard numeric values:
// IsValid() - Returns true if the underlying numeric value is valid (i.e. has
// has not wrapped and is not the result of an invalid conversion).
// ValueOrDie() - Returns the underlying value. If the state is not valid this
// call will crash on a CHECK.
// ValueOrDefault() - Returns the current value, or the supplied default if the
// state is not valid.
// ValueFloating() - Returns the underlying floating point value (valid only
// only for floating point CheckedNumeric types).
//
// Bitwise operations are explicitly not supported, because correct
// handling of some cases (e.g. sign manipulation) is ambiguous. Comparison
// operations are explicitly not supported because they could result in a crash
// on a CHECK condition. You should use patterns like the following for these
// operations:
// Bitwise operation:
// CheckedNumeric<int> checked_int = untrusted_input_value;
// int x = checked_int.ValueOrDefault(0) | kFlagValues;
// Comparison:
// CheckedNumeric<size_t> checked_size;
// CheckedNumeric<int> checked_size = untrusted_input_value;
// checked_size = checked_size + HEADER LENGTH;
// if (checked_size.IsValid() && checked_size.ValueOrDie() < buffer_size)
// Do stuff...
template <typename T>
class CheckedNumeric {
public:
typedef T type;
CheckedNumeric() {}
// Copy constructor.
template <typename Src>
CheckedNumeric(const CheckedNumeric<Src>& rhs)
: state_(rhs.ValueUnsafe(), rhs.validity()) {}
template <typename Src>
CheckedNumeric(Src value, RangeConstraint validity)
: state_(value, validity) {}
// This is not an explicit constructor because we implicitly upgrade regular
// numerics to CheckedNumerics to make them easier to use.
template <typename Src>
CheckedNumeric(Src value)
: state_(value) {
COMPILE_ASSERT(std::numeric_limits<Src>::is_specialized,
argument_must_be_numeric);
}
// IsValid() is the public API to test if a CheckedNumeric is currently valid.
bool IsValid() const { return validity() == RANGE_VALID; }
// ValueOrDie() The primary accessor for the underlying value. If the current
// state is not valid it will CHECK and crash.
T ValueOrDie() const {
CHECK(IsValid());
return state_.value();
}
// ValueOrDefault(T default_value) A convenience method that returns the
// current value if the state is valid, and the supplied default_value for
// any other state.
T ValueOrDefault(T default_value) const {
return IsValid() ? state_.value() : default_value;
}
// ValueFloating() - Since floating point values include their validity state,
// we provide an easy method for extracting them directly, without a risk of
// crashing on a CHECK.
T ValueFloating() const {
COMPILE_ASSERT(std::numeric_limits<T>::is_iec559, argument_must_be_float);
return CheckedNumeric<T>::cast(*this).ValueUnsafe();
}
// validity() - DO NOT USE THIS IN EXTERNAL CODE - It is public right now for
// tests and to avoid a big matrix of friend operator overloads. But the
// values it returns are likely to change in the future.
// Returns: current validity state (i.e. valid, overflow, underflow, nan).
// TODO(jschuh): crbug.com/332611 Figure out and implement semantics for
// saturation/wrapping so we can expose this state consistently and implement
// saturated arithmetic.
RangeConstraint validity() const { return state_.validity(); }
// ValueUnsafe() - DO NOT USE THIS IN EXTERNAL CODE - It is public right now
// for tests and to avoid a big matrix of friend operator overloads. But the
// values it returns are likely to change in the future.
// Returns: the raw numeric value, regardless of the current state.
// TODO(jschuh): crbug.com/332611 Figure out and implement semantics for
// saturation/wrapping so we can expose this state consistently and implement
// saturated arithmetic.
T ValueUnsafe() const { return state_.value(); }
// Prototypes for the supported arithmetic operator overloads.
template <typename Src> CheckedNumeric& operator+=(Src rhs);
template <typename Src> CheckedNumeric& operator-=(Src rhs);
template <typename Src> CheckedNumeric& operator*=(Src rhs);
template <typename Src> CheckedNumeric& operator/=(Src rhs);
template <typename Src> CheckedNumeric& operator%=(Src rhs);
CheckedNumeric operator-() const {
RangeConstraint validity;
T value = CheckedNeg(state_.value(), &validity);
// Negation is always valid for floating point.
if (std::numeric_limits<T>::is_iec559)
return CheckedNumeric<T>(value);
validity = GetRangeConstraint(state_.validity() | validity);
return CheckedNumeric<T>(value, validity);
}
CheckedNumeric Abs() const {
RangeConstraint validity;
T value = CheckedAbs(state_.value(), &validity);
// Absolute value is always valid for floating point.
if (std::numeric_limits<T>::is_iec559)
return CheckedNumeric<T>(value);
validity = GetRangeConstraint(state_.validity() | validity);
return CheckedNumeric<T>(value, validity);
}
CheckedNumeric& operator++() {
*this += 1;
return *this;
}
CheckedNumeric operator++(int) {
CheckedNumeric value = *this;
*this += 1;
return value;
}
CheckedNumeric& operator--() {
*this -= 1;
return *this;
}
CheckedNumeric operator--(int) {
CheckedNumeric value = *this;
*this -= 1;
return value;
}
// These static methods behave like a convenience cast operator targeting
// the desired CheckedNumeric type. As an optimization, a reference is
// returned when Src is the same type as T.
template <typename Src>
static CheckedNumeric<T> cast(
Src u,
typename enable_if<std::numeric_limits<Src>::is_specialized, int>::type =
0) {
return u;
}
template <typename Src>
static CheckedNumeric<T> cast(
const CheckedNumeric<Src>& u,
typename enable_if<!is_same<Src, T>::value, int>::type = 0) {
return u;
}
static const CheckedNumeric<T>& cast(const CheckedNumeric<T>& u) { return u; }
private:
CheckedNumericState<T> state_;
};
// This is the boilerplate for the standard arithmetic operator overloads. A
// macro isn't the prettiest solution, but it beats rewriting these five times.
// Some details worth noting are:
// * We apply the standard arithmetic promotions.
// * We skip range checks for floating points.
// * We skip range checks for destination integers with sufficient range.
// TODO(jschuh): extract these out into templates.
#define BASE_NUMERIC_ARITHMETIC_OPERATORS(NAME, OP, COMPOUND_OP) \
/* Binary arithmetic operator for CheckedNumerics of the same type. */ \
template <typename T> \
CheckedNumeric<typename ArithmeticPromotion<T>::type> operator OP( \
const CheckedNumeric<T>& lhs, const CheckedNumeric<T>& rhs) { \
typedef typename ArithmeticPromotion<T>::type Promotion; \
/* Floating point always takes the fast path */ \
if (std::numeric_limits<T>::is_iec559) \
return CheckedNumeric<T>(lhs.ValueUnsafe() OP rhs.ValueUnsafe()); \
if (IsIntegerArithmeticSafe<Promotion, T, T>::value) \
return CheckedNumeric<Promotion>( \
lhs.ValueUnsafe() OP rhs.ValueUnsafe(), \
GetRangeConstraint(rhs.validity() | lhs.validity())); \
RangeConstraint validity = RANGE_VALID; \
T result = Checked##NAME(static_cast<Promotion>(lhs.ValueUnsafe()), \
static_cast<Promotion>(rhs.ValueUnsafe()), \
&validity); \
return CheckedNumeric<Promotion>( \
result, \
GetRangeConstraint(validity | lhs.validity() | rhs.validity())); \
} \
/* Assignment arithmetic operator implementation from CheckedNumeric. */ \
template <typename T> \
template <typename Src> \
CheckedNumeric<T>& CheckedNumeric<T>::operator COMPOUND_OP(Src rhs) { \
*this = CheckedNumeric<T>::cast(*this) OP CheckedNumeric<Src>::cast(rhs); \
return *this; \
} \
/* Binary arithmetic operator for CheckedNumeric of different type. */ \
template <typename T, typename Src> \
CheckedNumeric<typename ArithmeticPromotion<T, Src>::type> operator OP( \
const CheckedNumeric<Src>& lhs, const CheckedNumeric<T>& rhs) { \
typedef typename ArithmeticPromotion<T, Src>::type Promotion; \
if (IsIntegerArithmeticSafe<Promotion, T, Src>::value) \
return CheckedNumeric<Promotion>( \
lhs.ValueUnsafe() OP rhs.ValueUnsafe(), \
GetRangeConstraint(rhs.validity() | lhs.validity())); \
return CheckedNumeric<Promotion>::cast(lhs) \
OP CheckedNumeric<Promotion>::cast(rhs); \
} \
/* Binary arithmetic operator for left CheckedNumeric and right numeric. */ \
template <typename T, typename Src> \
CheckedNumeric<typename ArithmeticPromotion<T, Src>::type> operator OP( \
const CheckedNumeric<T>& lhs, Src rhs) { \
typedef typename ArithmeticPromotion<T, Src>::type Promotion; \
if (IsIntegerArithmeticSafe<Promotion, T, Src>::value) \
return CheckedNumeric<Promotion>(lhs.ValueUnsafe() OP rhs, \
lhs.validity()); \
return CheckedNumeric<Promotion>::cast(lhs) \
OP CheckedNumeric<Promotion>::cast(rhs); \
} \
/* Binary arithmetic operator for right numeric and left CheckedNumeric. */ \
template <typename T, typename Src> \
CheckedNumeric<typename ArithmeticPromotion<T, Src>::type> operator OP( \
Src lhs, const CheckedNumeric<T>& rhs) { \
typedef typename ArithmeticPromotion<T, Src>::type Promotion; \
if (IsIntegerArithmeticSafe<Promotion, T, Src>::value) \
return CheckedNumeric<Promotion>(lhs OP rhs.ValueUnsafe(), \
rhs.validity()); \
return CheckedNumeric<Promotion>::cast(lhs) \
OP CheckedNumeric<Promotion>::cast(rhs); \
}
BASE_NUMERIC_ARITHMETIC_OPERATORS(Add, +, += )
BASE_NUMERIC_ARITHMETIC_OPERATORS(Sub, -, -= )
BASE_NUMERIC_ARITHMETIC_OPERATORS(Mul, *, *= )
BASE_NUMERIC_ARITHMETIC_OPERATORS(Div, /, /= )
BASE_NUMERIC_ARITHMETIC_OPERATORS(Mod, %, %= )
#undef BASE_NUMERIC_ARITHMETIC_OPERATORS
} // namespace internal
using internal::CheckedNumeric;
} // namespace base
#endif // BASE_SAFE_MATH_H_