iterators.hpp

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#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.

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

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

#include <protozero/config.hpp>
#include <protozero/varint.hpp>

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

namespace protozero {

template <typename T, typename P = std::pair<T, T>>
class iterator_range :
#ifdef PROTOZERO_STRICT_API
    protected
#else
    public
#endif
        P {

public:

    using iterator = T;

    using value_type = typename std::iterator_traits<T>::value_type;

    constexpr iterator_range() :
        P(iterator{}, iterator{}) {
    }

    constexpr iterator_range(iterator&& first_iterator, iterator&& last_iterator) :
        P(std::forward<iterator>(first_iterator),
          std::forward<iterator>(last_iterator)) {
    }

    constexpr iterator begin() const noexcept {
        return this->first;
    }

    constexpr iterator end() const noexcept {
        return this->second;
    }

    constexpr iterator cbegin() const noexcept {
        return this->first;
    }

    constexpr iterator cend() const noexcept {
        return this->second;
    }

    constexpr bool empty() const noexcept {
        return begin() == end();
    }

    std::size_t size() const noexcept {
        return begin().size();
    }

    value_type front() const {
        protozero_assert(!empty());
        return *(this->first);
    }

    void drop_front() {
        protozero_assert(!empty());
        ++this->first;
    }

    void swap(iterator_range& other) noexcept {
        using std::swap;
        swap(this->first, other.first);
        swap(this->second, other.second);
    }

}; // struct iterator_range

template <typename T>
inline void swap(iterator_range<T>& lhs, iterator_range<T>& rhs) noexcept {
    lhs.swap(rhs);
}

template <typename T>
class const_fixed_iterator {

    const char* m_data = nullptr;

    const char* m_end = nullptr;

public:

    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_fixed_iterator() noexcept = default;

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

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

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

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

    std::size_t size() const noexcept {
        return static_cast<std::size_t>(m_end - m_data) / sizeof(T);
    }

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

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

}; // class const_fixed_iterator

template <typename T>
class const_varint_iterator {

protected:

    const char* m_data = nullptr;

    const char* m_end = nullptr;

public:

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

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

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

    std::size_t size() const noexcept {
        // 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 static_cast<std::size_t>(std::count_if(m_data, m_end, [](char c) {
            return (static_cast<unsigned char>(c) & 0x80) == 0;
        }));
    }

    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);
    }

}; // class const_varint_iterator

template <typename T>
class const_svarint_iterator : public const_varint_iterator<T> {

public:

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

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

}; // class const_svarint_iterator

} // end namespace protozero

#endif // PROTOZERO_ITERATORS_HPP