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⚡ hash function without allocation

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Niels Lohmann 2020-07-14 14:31:19 +02:00
parent 1a521cbd36
commit 5b229f4cce
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GPG key ID: 7F3CEA63AE251B69
3 changed files with 191 additions and 6 deletions
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93
include/nlohmann/detail/hash.hpp Normal file
View file

@ -0,0 +1,93 @@
#pragma once
#include <functional> // hash
namespace nlohmann
{
namespace detail
{
std::size_t combine(std::size_t seed, std::size_t h)
{
seed ^= h + 0x9e3779b9 + (seed << 6U) + (seed >> 2U);
return seed;
}
template<typename BasicJsonType>
std::size_t hash(const BasicJsonType& j)
{
switch (j.type())
{
case BasicJsonType::value_t::null:
case BasicJsonType::discarded:
return combine(static_cast<std::size_t>(j.type()), 0);
case BasicJsonType::value_t::object:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.size());
for (const auto& element : j.items())
{
const auto h = std::hash<typename BasicJsonType::string_t> {}(element.key());
seed = combine(seed, h);
seed = combine(seed, hash(element.value()));
}
return seed;
}
case BasicJsonType::value_t::array:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.size());
for (const auto& element : j)
{
seed = combine(seed, hash(element));
}
return seed;
}
case BasicJsonType::value_t::string:
{
const auto h = std::hash<typename BasicJsonType::string_t> {}(j.template get_ref<const typename BasicJsonType::string_t&>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case BasicJsonType::value_t::boolean:
{
const auto h = std::hash<bool> {}(j.template get<bool>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case BasicJsonType::value_t::number_integer:
{
const auto h = std::hash<typename BasicJsonType::number_integer_t> {}(j.template get<typename BasicJsonType::number_integer_t>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case nlohmann::detail::value_t::number_unsigned:
{
const auto h = std::hash<typename BasicJsonType::number_unsigned_t> {}(j.template get<typename BasicJsonType::number_unsigned_t>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case nlohmann::detail::value_t::number_float:
{
const auto h = std::hash<typename BasicJsonType::number_float_t> {}(j.template get<typename BasicJsonType::number_float_t>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case nlohmann::detail::value_t::binary:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.get_binary().size());
seed = combine(seed, j.get_binary().subtype());
for (const auto byte : j.get_binary())
{
seed = combine(seed, std::hash<std::uint8_t> {}(byte));
}
return seed;
}
}
return 0;
}
} // namespace detail
} // namespace nlohmann

5
include/nlohmann/json.hpp
View file

@ -51,6 +51,7 @@ SOFTWARE.
#include <nlohmann/detail/conversions/from_json.hpp> #include <nlohmann/detail/conversions/from_json.hpp>
#include <nlohmann/detail/conversions/to_json.hpp> #include <nlohmann/detail/conversions/to_json.hpp>
#include <nlohmann/detail/exceptions.hpp> #include <nlohmann/detail/exceptions.hpp>
#include <nlohmann/detail/hash.hpp>
#include <nlohmann/detail/input/binary_reader.hpp> #include <nlohmann/detail/input/binary_reader.hpp>
#include <nlohmann/detail/input/input_adapters.hpp> #include <nlohmann/detail/input/input_adapters.hpp>
#include <nlohmann/detail/input/lexer.hpp> #include <nlohmann/detail/input/lexer.hpp>
@ -8698,9 +8699,7 @@ struct hash<nlohmann::json>
*/ */
std::size_t operator()(const nlohmann::json& j) const std::size_t operator()(const nlohmann::json& j) const
{ {
// a naive hashing via the string representation return nlohmann::detail::hash(j);
const auto& h = hash<nlohmann::json::string_t>();
return h(j.dump());
} }
}; };

99
single_include/nlohmann/json.hpp
View file

@ -4442,6 +4442,101 @@ class byte_container_with_subtype : public BinaryType
// #include <nlohmann/detail/exceptions.hpp> // #include <nlohmann/detail/exceptions.hpp>
// #include <nlohmann/detail/hash.hpp>
#include <functional> // hash
namespace nlohmann
{
namespace detail
{
std::size_t combine(std::size_t seed, std::size_t h)
{
seed ^= h + 0x9e3779b9 + (seed << 6U) + (seed >> 2U);
return seed;
}
template<typename BasicJsonType>
std::size_t hash(const BasicJsonType& j)
{
switch (j.type())
{
case BasicJsonType::value_t::null:
case BasicJsonType::discarded:
return combine(static_cast<std::size_t>(j.type()), 0);
case BasicJsonType::value_t::object:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.size());
for (const auto& element : j.items())
{
const auto h = std::hash<typename BasicJsonType::string_t> {}(element.key());
seed = combine(seed, h);
seed = combine(seed, hash(element.value()));
}
return seed;
}
case BasicJsonType::value_t::array:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.size());
for (const auto& element : j)
{
seed = combine(seed, hash(element));
}
return seed;
}
case BasicJsonType::value_t::string:
{
const auto h = std::hash<typename BasicJsonType::string_t> {}(j.template get_ref<const typename BasicJsonType::string_t&>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case BasicJsonType::value_t::boolean:
{
const auto h = std::hash<bool> {}(j.template get<bool>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case BasicJsonType::value_t::number_integer:
{
const auto h = std::hash<typename BasicJsonType::number_integer_t> {}(j.template get<typename BasicJsonType::number_integer_t>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case nlohmann::detail::value_t::number_unsigned:
{
const auto h = std::hash<typename BasicJsonType::number_unsigned_t> {}(j.template get<typename BasicJsonType::number_unsigned_t>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case nlohmann::detail::value_t::number_float:
{
const auto h = std::hash<typename BasicJsonType::number_float_t> {}(j.template get<typename BasicJsonType::number_float_t>());
return combine(static_cast<std::size_t>(j.type()), h);
}
case nlohmann::detail::value_t::binary:
{
auto seed = combine(static_cast<std::size_t>(j.type()), j.get_binary().size());
seed = combine(seed, j.get_binary().subtype());
for (const auto byte : j.get_binary())
{
seed = combine(seed, std::hash<std::uint8_t> {}(byte));
}
return seed;
}
}
return 0;
}
} // namespace detail
} // namespace nlohmann
// #include <nlohmann/detail/input/binary_reader.hpp> // #include <nlohmann/detail/input/binary_reader.hpp>
@ -24686,9 +24781,7 @@ struct hash<nlohmann::json>
*/ */
std::size_t operator()(const nlohmann::json& j) const std::size_t operator()(const nlohmann::json& j) const
{ {
// a naive hashing via the string representation return nlohmann::detail::hash(j);
const auto& h = hash<nlohmann::json::string_t>();
return h(j.dump());
} }
}; };