hash_append.h

#pragma once
 
#include <boost/container/flat_set.hpp>
#include <boost/endian/conversion.hpp>
 
#include <array>
#include <chrono>
#include <cstring>
#include <functional>
#include <memory>
#include <string>
#include <system_error>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
 
namespace beast {
 
namespace detail {
 
template <class T>
/*constexpr*/
inline void
reverse_bytes(T& t)
{
    unsigned char* bytes =
        static_cast<unsigned char*>(std::memmove(std::addressof(t), std::addressof(t), sizeof(T)));
    for (unsigned i = 0; i < sizeof(T) / 2; ++i)
        std::swap(bytes[i], bytes[sizeof(T) - 1 - i]);
}
 
template <class T>
/*constexpr*/
inline void
maybe_reverse_bytes(T& t, std::false_type)
{
}
 
template <class T>
/*constexpr*/
inline void
maybe_reverse_bytes(T& t, std::true_type)
{
    reverse_bytes(t);
}
 
template <class T, class Hasher>
/*constexpr*/
inline void
maybe_reverse_bytes(T& t, Hasher&)
{
    maybe_reverse_bytes(
        t, std::integral_constant<bool, Hasher::endian != boost::endian::order::native>{});
}
 
}  // namespace detail
 
// is_uniquely_represented<T>
 
// A type T is contiguously hashable if for all combinations of two values of
// a type, say x and y, if x == y, then it must also be true that
// memcmp(addressof(x), addressof(y), sizeof(T)) == 0. I.e. if x == y,
// then x and y have the same bit pattern representation.
 
template <class T>
struct is_uniquely_represented
    : public std::integral_constant<
          bool,
          std::is_integral<T>::value || std::is_enum<T>::value || std::is_pointer<T>::value>
{
    explicit is_uniquely_represented() = default;
};
 
template <class T>
struct is_uniquely_represented<T const> : public is_uniquely_represented<T>
{
    explicit is_uniquely_represented() = default;
};
 
template <class T>
struct is_uniquely_represented<T volatile> : public is_uniquely_represented<T>
{
    explicit is_uniquely_represented() = default;
};
 
template <class T>
struct is_uniquely_represented<T const volatile> : public is_uniquely_represented<T>
{
    explicit is_uniquely_represented() = default;
};
 
// is_uniquely_represented<std::pair<T, U>>
 
template <class T, class U>
struct is_uniquely_represented<std::pair<T, U>>
    : public std::integral_constant<
          bool,
          is_uniquely_represented<T>::value && is_uniquely_represented<U>::value &&
              sizeof(T) + sizeof(U) == sizeof(std::pair<T, U>)>
{
    explicit is_uniquely_represented() = default;
};
 
// is_uniquely_represented<std::tuple<T...>>
 
template <class... T>
struct is_uniquely_represented<std::tuple<T...>>
    : public std::integral_constant<
          bool,
          std::conjunction_v<is_uniquely_represented<T>...> &&
              sizeof(std::tuple<T...>) == (sizeof(T) + ...)>
{
    explicit is_uniquely_represented() = default;
};
 
// is_uniquely_represented<T[N]>
 
template <class T, std::size_t N>
struct is_uniquely_represented<T[N]> : public is_uniquely_represented<T>
{
    explicit is_uniquely_represented() = default;
};
 
// is_uniquely_represented<std::array<T, N>>
 
template <class T, std::size_t N>
struct is_uniquely_represented<std::array<T, N>>
    : public std::integral_constant<
          bool,
          is_uniquely_represented<T>::value && sizeof(T) * N == sizeof(std::array<T, N>)>
{
    explicit is_uniquely_represented() = default;
};
 
template <class T, class HashAlgorithm>
struct is_contiguously_hashable
    : public std::integral_constant<
          bool,
          is_uniquely_represented<T>::value &&
              (sizeof(T) == 1 || HashAlgorithm::endian == boost::endian::order::native)>
{
    explicit is_contiguously_hashable() = default;
};
 
template <class T, std::size_t N, class HashAlgorithm>
struct is_contiguously_hashable<T[N], HashAlgorithm>
    : public std::integral_constant<
          bool,
          is_uniquely_represented<T[N]>::value &&
              (sizeof(T) == 1 || HashAlgorithm::endian == boost::endian::order::native)>
{
    explicit is_contiguously_hashable() = default;
};
//------------------------------------------------------------------------------
 
// scalars
 
template <class Hasher, class T>
inline std::enable_if_t<is_contiguously_hashable<T, Hasher>::value>
hash_append(Hasher& h, T const& t) noexcept
{
    h(std::addressof(t), sizeof(t));
}
 
template <class Hasher, class T>
inline std::enable_if_t<
    !is_contiguously_hashable<T, Hasher>::value &&
    (std::is_integral<T>::value || std::is_pointer<T>::value || std::is_enum<T>::value)>
hash_append(Hasher& h, T t) noexcept
{
    detail::reverse_bytes(t);
    h(std::addressof(t), sizeof(t));
}
 
template <class Hasher, class T>
inline std::enable_if_t<std::is_floating_point<T>::value>
hash_append(Hasher& h, T t) noexcept
{
    if (t == 0)
        t = 0;
    detail::maybe_reverse_bytes(t, h);
    h(&t, sizeof(t));
}
 
template <class Hasher>
inline void
hash_append(Hasher& h, std::nullptr_t) noexcept
{
    void const* p = nullptr;
    detail::maybe_reverse_bytes(p, h);
    h(&p, sizeof(p));
}
 
// Forward declarations for ADL purposes
 
template <class Hasher, class T, std::size_t N>
std::enable_if_t<!is_contiguously_hashable<T, Hasher>::value>
hash_append(Hasher& h, T (&a)[N]) noexcept;
 
template <class Hasher, class CharT, class Traits, class Alloc>
std::enable_if_t<!is_contiguously_hashable<CharT, Hasher>::value>
hash_append(Hasher& h, std::basic_string<CharT, Traits, Alloc> const& s) noexcept;
 
template <class Hasher, class CharT, class Traits, class Alloc>
std::enable_if_t<is_contiguously_hashable<CharT, Hasher>::value>
hash_append(Hasher& h, std::basic_string<CharT, Traits, Alloc> const& s) noexcept;
 
template <class Hasher, class T, class U>
std::enable_if_t<!is_contiguously_hashable<std::pair<T, U>, Hasher>::value>
hash_append(Hasher& h, std::pair<T, U> const& p) noexcept;
 
template <class Hasher, class T, class Alloc>
std::enable_if_t<!is_contiguously_hashable<T, Hasher>::value>
hash_append(Hasher& h, std::vector<T, Alloc> const& v) noexcept;
 
template <class Hasher, class T, class Alloc>
std::enable_if_t<is_contiguously_hashable<T, Hasher>::value>
hash_append(Hasher& h, std::vector<T, Alloc> const& v) noexcept;
 
template <class Hasher, class T, std::size_t N>
std::enable_if_t<!is_contiguously_hashable<std::array<T, N>, Hasher>::value>
hash_append(Hasher& h, std::array<T, N> const& a) noexcept;
 
template <class Hasher, class... T>
std::enable_if_t<!is_contiguously_hashable<std::tuple<T...>, Hasher>::value>
hash_append(Hasher& h, std::tuple<T...> const& t) noexcept;
 
template <class Hasher, class Key, class T, class Hash, class Pred, class Alloc>
void
hash_append(Hasher& h, std::unordered_map<Key, T, Hash, Pred, Alloc> const& m);
 
template <class Hasher, class Key, class Hash, class Pred, class Alloc>
void
hash_append(Hasher& h, std::unordered_set<Key, Hash, Pred, Alloc> const& s);
 
template <class Hasher, class Key, class Compare, class Alloc>
std::enable_if_t<!is_contiguously_hashable<Key, Hasher>::value>
hash_append(Hasher& h, boost::container::flat_set<Key, Compare, Alloc> const& v) noexcept;
template <class Hasher, class Key, class Compare, class Alloc>
std::enable_if_t<is_contiguously_hashable<Key, Hasher>::value>
hash_append(Hasher& h, boost::container::flat_set<Key, Compare, Alloc> const& v) noexcept;
template <class Hasher, class T0, class T1, class... T>
void
hash_append(Hasher& h, T0 const& t0, T1 const& t1, T const&... t) noexcept;
 
// c-array
 
template <class Hasher, class T, std::size_t N>
std::enable_if_t<!is_contiguously_hashable<T, Hasher>::value>
hash_append(Hasher& h, T (&a)[N]) noexcept
{
    for (auto const& t : a)
        hash_append(h, t);
}
 
// basic_string
 
template <class Hasher, class CharT, class Traits, class Alloc>
inline std::enable_if_t<!is_contiguously_hashable<CharT, Hasher>::value>
hash_append(Hasher& h, std::basic_string<CharT, Traits, Alloc> const& s) noexcept
{
    for (auto c : s)
        hash_append(h, c);
    hash_append(h, s.size());
}
 
template <class Hasher, class CharT, class Traits, class Alloc>
inline std::enable_if_t<is_contiguously_hashable<CharT, Hasher>::value>
hash_append(Hasher& h, std::basic_string<CharT, Traits, Alloc> const& s) noexcept
{
    h(s.data(), s.size() * sizeof(CharT));
    hash_append(h, s.size());
}
 
// pair
 
template <class Hasher, class T, class U>
inline std::enable_if_t<!is_contiguously_hashable<std::pair<T, U>, Hasher>::value>
hash_append(Hasher& h, std::pair<T, U> const& p) noexcept
{
    hash_append(h, p.first, p.second);
}
 
// vector
 
template <class Hasher, class T, class Alloc>
inline std::enable_if_t<!is_contiguously_hashable<T, Hasher>::value>
hash_append(Hasher& h, std::vector<T, Alloc> const& v) noexcept
{
    for (auto const& t : v)
        hash_append(h, t);
    hash_append(h, v.size());
}
 
template <class Hasher, class T, class Alloc>
inline std::enable_if_t<is_contiguously_hashable<T, Hasher>::value>
hash_append(Hasher& h, std::vector<T, Alloc> const& v) noexcept
{
    h(v.data(), v.size() * sizeof(T));
    hash_append(h, v.size());
}
 
// array
 
template <class Hasher, class T, std::size_t N>
std::enable_if_t<!is_contiguously_hashable<std::array<T, N>, Hasher>::value>
hash_append(Hasher& h, std::array<T, N> const& a) noexcept
{
    for (auto const& t : a)
        hash_append(h, t);
}
 
template <class Hasher, class Key, class Compare, class Alloc>
std::enable_if_t<!is_contiguously_hashable<Key, Hasher>::value>
hash_append(Hasher& h, boost::container::flat_set<Key, Compare, Alloc> const& v) noexcept
{
    for (auto const& t : v)
        hash_append(h, t);
}
template <class Hasher, class Key, class Compare, class Alloc>
std::enable_if_t<is_contiguously_hashable<Key, Hasher>::value>
hash_append(Hasher& h, boost::container::flat_set<Key, Compare, Alloc> const& v) noexcept
{
    h(&(v.begin()), v.size() * sizeof(Key));
}
// tuple
 
namespace detail {
 
inline void
for_each_item(...) noexcept
{
}
 
template <class Hasher, class T>
inline int
hash_one(Hasher& h, T const& t) noexcept
{
    hash_append(h, t);
    return 0;
}
 
template <class Hasher, class... T, std::size_t... I>
inline void
tuple_hash(Hasher& h, std::tuple<T...> const& t, std::index_sequence<I...>) noexcept
{
    for_each_item(hash_one(h, std::get<I>(t))...);
}
 
}  // namespace detail
 
template <class Hasher, class... T>
inline std::enable_if_t<!is_contiguously_hashable<std::tuple<T...>, Hasher>::value>
hash_append(Hasher& h, std::tuple<T...> const& t) noexcept
{
    detail::tuple_hash(h, t, std::index_sequence_for<T...>{});
}
 
// shared_ptr
 
template <class Hasher, class T>
inline void
hash_append(Hasher& h, std::shared_ptr<T> const& p) noexcept
{
    hash_append(h, p.get());
}
 
// chrono
 
template <class Hasher, class Rep, class Period>
inline void
hash_append(Hasher& h, std::chrono::duration<Rep, Period> const& d) noexcept
{
    hash_append(h, d.count());
}
 
template <class Hasher, class Clock, class Duration>
inline void
hash_append(Hasher& h, std::chrono::time_point<Clock, Duration> const& tp) noexcept
{
    hash_append(h, tp.time_since_epoch());
}
 
// variadic
 
template <class Hasher, class T0, class T1, class... T>
inline void
hash_append(Hasher& h, T0 const& t0, T1 const& t1, T const&... t) noexcept
{
    hash_append(h, t0);
    hash_append(h, t1, t...);
}
 
// error_code
 
template <class HashAlgorithm>
inline void
hash_append(HashAlgorithm& h, std::error_code const& ec)
{
    hash_append(h, ec.value(), &ec.category());
}
 
}  // namespace beast