include/protozero/iterators.hpp

#ifndef PROTOZERO_ITERATORS_HPP
#define PROTOZERO_ITERATORS_HPP

/*****************************************************************************

protozero - Minimalistic protocol buffer decoder and encoder in C++.

This file is from https://github.com/mapbox/protozero where you can find more
documentation.

*****************************************************************************/

/**
 * @file iterators.hpp
 *
 * @brief Contains the iterators for access to packed repeated fields.
 */

#include "config.hpp"
#include "varint.hpp"

#if PROTOZERO_BYTE_ORDER != PROTOZERO_LITTLE_ENDIAN
# include <protozero/byteswap.hpp>
#endif

#include <algorithm>
#include <cstring>
#include <iterator>
#include <utility>

namespace protozero {

/**
 * A range of iterators based on std::pair. Created from beginning and
 * end iterators. Used as a return type from some pbf_reader methods
 * that is easy to use with range-based for loops.
 */
template <typename T, typename P = std::pair<T, T>>
class iterator_range :
#ifdef PROTOZERO_STRICT_API
    protected
#else
    public
#endif
        P {

public:

    /// The type of the iterators in this range.
    using iterator = T;

    /// The value type of the underlying iterator.
    using value_type = typename std::iterator_traits<T>::value_type;

    /**
     * Default constructor. Create empty iterator_range.
     */
    constexpr iterator_range() :
        P{iterator{}, iterator{}} {
    }

    /**
     * Create iterator range from two iterators.
     *
     * @param first_iterator Iterator to beginning of range.
     * @param last_iterator Iterator to end of range.
     */
    constexpr iterator_range(iterator&& first_iterator, iterator&& last_iterator) :
        P{std::forward<iterator>(first_iterator),
          std::forward<iterator>(last_iterator)} {
    }

    /// Return iterator to beginning of range.
    constexpr iterator begin() const noexcept {
        return this->first;
    }

    /// Return iterator to end of range.
    constexpr iterator end() const noexcept {
        return this->second;
    }

    /// Return iterator to beginning of range.
    constexpr iterator cbegin() const noexcept {
        return this->first;
    }

    /// Return iterator to end of range.
    constexpr iterator cend() const noexcept {
        return this->second;
    }

    /**
     * Return true if this range is empty.
     *
     * Complexity: Constant.
     */
    constexpr bool empty() const noexcept {
        return begin() == end();
    }

    /**
     * Get the size of the range, ie the number of elements it contains.
     *
     * Complexity: Constant or linear depending on the underlaying iterator.
     */
    std::size_t size() const noexcept {
        return static_cast<size_t>(std::distance(begin(), end()));
    }

    /**
     * Get element at the beginning of the range.
     *
     * @pre Range must not be empty.
     */
    value_type front() const {
        protozero_assert(!empty());
        return *(this->first);
    }

    /**
     * Advance beginning of range by one.
     *
     * @pre Range must not be empty.
     */
    void drop_front() {
        protozero_assert(!empty());
        ++this->first;
    }

    /**
     * Swap the contents of this range with the other.
     *
     * @param other Other range to swap data with.
     */
    void swap(iterator_range& other) noexcept {
        using std::swap;
        swap(this->first, other.first);
        swap(this->second, other.second);
    }

}; // struct iterator_range

/**
 * Swap two iterator_ranges.
 *
 * @param lhs First range.
 * @param rhs Second range.
 */
template <typename T>
inline void swap(iterator_range<T>& lhs, iterator_range<T>& rhs) noexcept {
    lhs.swap(rhs);
}

/**
 * A forward iterator used for accessing packed repeated fields of fixed
 * length (fixed32, sfixed32, float, double).
 */
template <typename T>
class const_fixed_iterator {

    /// Pointer to current iterator position
    const char* m_data = nullptr;

public:

    /// @cond usual iterator functions not documented

    using iterator_category = std::random_access_iterator_tag;
    using value_type        = T;
    using difference_type   = std::ptrdiff_t;
    using pointer           = value_type*;
    using reference         = value_type&;

    const_fixed_iterator() noexcept = default;

    explicit const_fixed_iterator(const char* data) noexcept :
        m_data{data} {
    }

    const_fixed_iterator(const const_fixed_iterator&) noexcept = default;
    const_fixed_iterator(const_fixed_iterator&&) noexcept = default;

    const_fixed_iterator& operator=(const const_fixed_iterator&) noexcept = default;
    const_fixed_iterator& operator=(const_fixed_iterator&&) noexcept = default;

    ~const_fixed_iterator() noexcept = default;

    value_type operator*() const noexcept {
        value_type result;
        std::memcpy(&result, m_data, sizeof(value_type));
#if PROTOZERO_BYTE_ORDER != PROTOZERO_LITTLE_ENDIAN
        byteswap_inplace(&result);
#endif
        return result;
    }

    const_fixed_iterator& operator++() noexcept {
        m_data += sizeof(value_type);
        return *this;
    }

    const_fixed_iterator operator++(int) noexcept {
        const const_fixed_iterator tmp{*this};
        ++(*this);
        return tmp;
    }

    const_fixed_iterator& operator--() noexcept {
        m_data -= sizeof(value_type);
        return *this;
    }

    const_fixed_iterator operator--(int) noexcept {
        const const_fixed_iterator tmp{*this};
        --(*this);
        return tmp;
    }

    friend bool operator==(const_fixed_iterator lhs, const_fixed_iterator rhs) noexcept {
        return lhs.m_data == rhs.m_data;
    }

    friend bool operator!=(const_fixed_iterator lhs, const_fixed_iterator rhs) noexcept {
        return !(lhs == rhs);
    }

    friend bool operator<(const_fixed_iterator lhs, const_fixed_iterator rhs) noexcept {
        return lhs.m_data < rhs.m_data;
    }

    friend bool operator>(const_fixed_iterator lhs, const_fixed_iterator rhs) noexcept {
        return rhs < lhs;
    }

    friend bool operator<=(const_fixed_iterator lhs, const_fixed_iterator rhs) noexcept {
        return !(lhs > rhs);
    }

    friend bool operator>=(const_fixed_iterator lhs, const_fixed_iterator rhs) noexcept {
        return !(lhs < rhs);
    }

    const_fixed_iterator& operator+=(difference_type val) noexcept {
        m_data += (sizeof(value_type) * val);
        return *this;
    }

    friend const_fixed_iterator operator+(const_fixed_iterator lhs, difference_type rhs) noexcept {
        const_fixed_iterator tmp{lhs};
        tmp.m_data += (sizeof(value_type) * rhs);
        return tmp;
    }

    friend const_fixed_iterator operator+(difference_type lhs, const_fixed_iterator rhs) noexcept {
        const_fixed_iterator tmp{rhs};
        tmp.m_data += (sizeof(value_type) * lhs);
        return tmp;
    }

    const_fixed_iterator& operator-=(difference_type val) noexcept {
        m_data -= (sizeof(value_type) * val);
        return *this;
    }

    friend const_fixed_iterator operator-(const_fixed_iterator lhs, difference_type rhs) noexcept {
        const_fixed_iterator tmp{lhs};
        tmp.m_data -= (sizeof(value_type) * rhs);
        return tmp;
    }

    friend difference_type operator-(const_fixed_iterator lhs, const_fixed_iterator rhs) noexcept {
        return static_cast<difference_type>(lhs.m_data - rhs.m_data) / static_cast<difference_type>(sizeof(T));
    }

    value_type operator[](difference_type n) const noexcept {
        return *(*this + n);
    }

    /// @endcond

}; // class const_fixed_iterator

/**
 * A forward iterator used for accessing packed repeated varint fields
 * (int32, uint32, int64, uint64, bool, enum).
 */
template <typename T>
class const_varint_iterator {

protected:

    /// Pointer to current iterator position
    const char* m_data = nullptr; // NOLINT(misc-non-private-member-variables-in-classes, cppcoreguidelines-non-private-member-variables-in-classes,-warnings-as-errors)

    /// Pointer to end iterator position
    const char* m_end = nullptr; // NOLINT(misc-non-private-member-variables-in-classes, cppcoreguidelines-non-private-member-variables-in-classes,-warnings-as-errors)

public:

    /// @cond usual iterator functions not documented

    using iterator_category = std::forward_iterator_tag;
    using value_type        = T;
    using difference_type   = std::ptrdiff_t;
    using pointer           = value_type*;
    using reference         = value_type&;

    static difference_type distance(const_varint_iterator begin, const_varint_iterator end) noexcept {
        // The "distance" between default initialized const_varint_iterator's
        // is always 0.
        if (!begin.m_data) {
            return 0;
        }
        // We know that each varint contains exactly one byte with the most
        // significant bit not set. We can use this to quickly figure out
        // how many varints there are without actually decoding the varints.
        return std::count_if(begin.m_data, end.m_data, [](char c) noexcept {
            return (static_cast<unsigned char>(c) & 0x80U) == 0;
        });
    }

    const_varint_iterator() noexcept = default;

    const_varint_iterator(const char* data, const char* end) noexcept :
        m_data{data},
        m_end{end} {
    }

    const_varint_iterator(const const_varint_iterator&) noexcept = default;
    const_varint_iterator(const_varint_iterator&&) noexcept = default;

    const_varint_iterator& operator=(const const_varint_iterator&) noexcept = default;
    const_varint_iterator& operator=(const_varint_iterator&&) noexcept = default;

    ~const_varint_iterator() noexcept = default;

    value_type operator*() const {
        protozero_assert(m_data);
        const char* d = m_data; // will be thrown away
        return static_cast<value_type>(decode_varint(&d, m_end));
    }

    const_varint_iterator& operator++() {
        protozero_assert(m_data);
        skip_varint(&m_data, m_end);
        return *this;
    }

    const_varint_iterator operator++(int) {
        protozero_assert(m_data);
        const const_varint_iterator tmp{*this};
        ++(*this);
        return tmp;
    }

    bool operator==(const const_varint_iterator& rhs) const noexcept {
        return m_data == rhs.m_data && m_end == rhs.m_end;
    }

    bool operator!=(const const_varint_iterator& rhs) const noexcept {
        return !(*this == rhs);
    }

    /// @endcond

}; // class const_varint_iterator

/**
 * A forward iterator used for accessing packed repeated svarint fields
 * (sint32, sint64).
 */
template <typename T>
class const_svarint_iterator : public const_varint_iterator<T> {

public:

    /// @cond usual iterator functions not documented

    using iterator_category = std::forward_iterator_tag;
    using value_type        = T;
    using difference_type   = std::ptrdiff_t;
    using pointer           = value_type*;
    using reference         = value_type&;

    const_svarint_iterator() noexcept :
        const_varint_iterator<T>{} {
    }

    const_svarint_iterator(const char* data, const char* end) noexcept :
        const_varint_iterator<T>{data, end} {
    }

    const_svarint_iterator(const const_svarint_iterator&) = default;
    const_svarint_iterator(const_svarint_iterator&&) noexcept = default;

    const_svarint_iterator& operator=(const const_svarint_iterator&) = default;
    const_svarint_iterator& operator=(const_svarint_iterator&&) noexcept = default;

    ~const_svarint_iterator() = default;

    value_type operator*() const {
        protozero_assert(this->m_data);
        const char* d = this->m_data; // will be thrown away
        return static_cast<value_type>(decode_zigzag64(decode_varint(&d, this->m_end)));
    }

    const_svarint_iterator& operator++() {
        protozero_assert(this->m_data);
        skip_varint(&this->m_data, this->m_end);
        return *this;
    }

    const_svarint_iterator operator++(int) {
        protozero_assert(this->m_data);
        const const_svarint_iterator tmp{*this};
        ++(*this);
        return tmp;
    }

    /// @endcond

}; // class const_svarint_iterator

} // end namespace protozero

namespace std {

    // Specialize std::distance for all the protozero iterators. Because
    // functions can't be partially specialized, we have to do this for
    // every value_type we are using.

    /// @cond individual overloads do not need to be documented

    template <>
    inline typename protozero::const_varint_iterator<int32_t>::difference_type
    distance<protozero::const_varint_iterator<int32_t>>(protozero::const_varint_iterator<int32_t> first, // NOLINT(readability-inconsistent-declaration-parameter-name)
                                                        protozero::const_varint_iterator<int32_t> last) {
        return protozero::const_varint_iterator<int32_t>::distance(first, last);
    }

    template <>
    inline typename protozero::const_varint_iterator<int64_t>::difference_type
    distance<protozero::const_varint_iterator<int64_t>>(protozero::const_varint_iterator<int64_t> first, // NOLINT(readability-inconsistent-declaration-parameter-name)
                                                        protozero::const_varint_iterator<int64_t> last) {
        return protozero::const_varint_iterator<int64_t>::distance(first, last);
    }

    template <>
    inline typename protozero::const_varint_iterator<uint32_t>::difference_type
    distance<protozero::const_varint_iterator<uint32_t>>(protozero::const_varint_iterator<uint32_t> first, // NOLINT(readability-inconsistent-declaration-parameter-name)
                                                         protozero::const_varint_iterator<uint32_t> last) {
        return protozero::const_varint_iterator<uint32_t>::distance(first, last);
    }

    template <>
    inline typename protozero::const_varint_iterator<uint64_t>::difference_type
    distance<protozero::const_varint_iterator<uint64_t>>(protozero::const_varint_iterator<uint64_t> first, // NOLINT(readability-inconsistent-declaration-parameter-name)
                                                         protozero::const_varint_iterator<uint64_t> last) {
        return protozero::const_varint_iterator<uint64_t>::distance(first, last);
    }

    template <>
    inline typename protozero::const_svarint_iterator<int32_t>::difference_type
    distance<protozero::const_svarint_iterator<int32_t>>(protozero::const_svarint_iterator<int32_t> first, // NOLINT(readability-inconsistent-declaration-parameter-name)
                                                         protozero::const_svarint_iterator<int32_t> last) {
        return protozero::const_svarint_iterator<int32_t>::distance(first, last);
    }

    template <>
    inline typename protozero::const_svarint_iterator<int64_t>::difference_type
    distance<protozero::const_svarint_iterator<int64_t>>(protozero::const_svarint_iterator<int64_t> first, // NOLINT(readability-inconsistent-declaration-parameter-name)
                                                         protozero::const_svarint_iterator<int64_t> last) {
        return protozero::const_svarint_iterator<int64_t>::distance(first, last);
    }

    /// @endcond

} // end namespace std

#endif // PROTOZERO_ITERATORS_HPP