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// Copyright 2018 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_CONTAINERS_CHECKED_ITERATORS_H_
#define BASE_CONTAINERS_CHECKED_ITERATORS_H_
#include <iterator>
#include <memory>
#include <type_traits>
#include "base/containers/util.h"
#include "base/logging.h"
namespace base {
template <typename T>
class CheckedContiguousIterator {
public:
using difference_type = std::ptrdiff_t;
using value_type = std::remove_cv_t<T>;
using pointer = T*;
using reference = T&;
using iterator_category = std::random_access_iterator_tag;
// Required for converting constructor below.
template <typename U>
friend class CheckedContiguousIterator;
constexpr CheckedContiguousIterator() = default;
constexpr CheckedContiguousIterator(T* start, const T* end)
: CheckedContiguousIterator(start, start, end) {}
constexpr CheckedContiguousIterator(const T* start, T* current, const T* end)
: start_(start), current_(current), end_(end) {
CHECK_LE(start, current);
CHECK_LE(current, end);
}
constexpr CheckedContiguousIterator(const CheckedContiguousIterator& other) =
default;
// Converting constructor allowing conversions like CCI<T> to CCI<const T>,
// but disallowing CCI<const T> to CCI<T> or CCI<Derived> to CCI<Base>, which
// are unsafe. Furthermore, this is the same condition as used by the
// converting constructors of std::span<T> and std::unique_ptr<T[]>.
// See https://wg21.link/n4042 for details.
template <
typename U,
std::enable_if_t<std::is_convertible<U (*)[], T (*)[]>::value>* = nullptr>
constexpr CheckedContiguousIterator(const CheckedContiguousIterator<U>& other)
: start_(other.start_), current_(other.current_), end_(other.end_) {
// We explicitly don't delegate to the 3-argument constructor here. Its
// CHECKs would be redundant, since we expect |other| to maintain its own
// invariant. However, DCHECKs never hurt anybody. Presumably.
DCHECK_LE(other.start_, other.current_);
DCHECK_LE(other.current_, other.end_);
}
~CheckedContiguousIterator() = default;
constexpr CheckedContiguousIterator& operator=(
const CheckedContiguousIterator& other) = default;
constexpr bool operator==(const CheckedContiguousIterator& other) const {
CheckComparable(other);
return current_ == other.current_;
}
constexpr bool operator!=(const CheckedContiguousIterator& other) const {
CheckComparable(other);
return current_ != other.current_;
}
constexpr bool operator<(const CheckedContiguousIterator& other) const {
CheckComparable(other);
return current_ < other.current_;
}
constexpr bool operator<=(const CheckedContiguousIterator& other) const {
CheckComparable(other);
return current_ <= other.current_;
}
constexpr bool operator>(const CheckedContiguousIterator& other) const {
CheckComparable(other);
return current_ > other.current_;
}
constexpr bool operator>=(const CheckedContiguousIterator& other) const {
CheckComparable(other);
return current_ >= other.current_;
}
constexpr CheckedContiguousIterator& operator++() {
CHECK_NE(current_, end_);
++current_;
return *this;
}
constexpr CheckedContiguousIterator operator++(int) {
CheckedContiguousIterator old = *this;
++*this;
return old;
}
constexpr CheckedContiguousIterator& operator--() {
CHECK_NE(current_, start_);
--current_;
return *this;
}
constexpr CheckedContiguousIterator operator--(int) {
CheckedContiguousIterator old = *this;
--*this;
return old;
}
constexpr CheckedContiguousIterator& operator+=(difference_type rhs) {
if (rhs > 0) {
CHECK_LE(rhs, end_ - current_);
} else {
CHECK_LE(-rhs, current_ - start_);
}
current_ += rhs;
return *this;
}
constexpr CheckedContiguousIterator operator+(difference_type rhs) const {
CheckedContiguousIterator it = *this;
it += rhs;
return it;
}
constexpr CheckedContiguousIterator& operator-=(difference_type rhs) {
if (rhs < 0) {
CHECK_LE(-rhs, end_ - current_);
} else {
CHECK_LE(rhs, current_ - start_);
}
current_ -= rhs;
return *this;
}
constexpr CheckedContiguousIterator operator-(difference_type rhs) const {
CheckedContiguousIterator it = *this;
it -= rhs;
return it;
}
constexpr friend difference_type operator-(
const CheckedContiguousIterator& lhs,
const CheckedContiguousIterator& rhs) {
CHECK_EQ(lhs.start_, rhs.start_);
CHECK_EQ(lhs.end_, rhs.end_);
return lhs.current_ - rhs.current_;
}
constexpr reference operator*() const {
CHECK_NE(current_, end_);
return *current_;
}
constexpr pointer operator->() const {
CHECK_NE(current_, end_);
return current_;
}
constexpr reference operator[](difference_type rhs) const {
CHECK_GE(rhs, 0);
CHECK_LT(rhs, end_ - current_);
return current_[rhs];
}
static bool IsRangeMoveSafe(const CheckedContiguousIterator& from_begin,
const CheckedContiguousIterator& from_end,
const CheckedContiguousIterator& to)
WARN_UNUSED_RESULT {
if (from_end < from_begin)
return false;
const auto from_begin_uintptr = get_uintptr(from_begin.current_);
const auto from_end_uintptr = get_uintptr(from_end.current_);
const auto to_begin_uintptr = get_uintptr(to.current_);
const auto to_end_uintptr =
get_uintptr((to + std::distance(from_begin, from_end)).current_);
return to_begin_uintptr >= from_end_uintptr ||
to_end_uintptr <= from_begin_uintptr;
}
private:
constexpr void CheckComparable(const CheckedContiguousIterator& other) const {
CHECK_EQ(start_, other.start_);
CHECK_EQ(end_, other.end_);
}
const T* start_ = nullptr;
T* current_ = nullptr;
const T* end_ = nullptr;
};
template <typename T>
using CheckedContiguousConstIterator = CheckedContiguousIterator<const T>;
} // namespace base
#endif // BASE_CONTAINERS_CHECKED_ITERATORS_H_
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