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// Copyright 2021 The Tint Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef SRC_TINT_UTILS_HASH_H_
#define SRC_TINT_UTILS_HASH_H_
#include <stdint.h>
#include <cstdio>
#include <functional>
#include <tuple>
#include <utility>
#include <variant>
#include <vector>
#include "src/tint/utils/crc32.h"
#include "src/tint/utils/vector.h"
namespace tint::utils {
namespace detail {
/// Helper for obtaining a seed bias value for HashCombine with a bit-width
/// dependent on the size of size_t.
template <int SIZE_OF_SIZE_T>
struct HashCombineOffset {};
/// Specialization of HashCombineOffset for size_t == 4.
template <>
struct HashCombineOffset<4> {
/// @returns the seed bias value for HashCombine()
static constexpr inline uint32_t value() {
constexpr uint32_t base = 0x7f4a7c16;
#ifdef TINT_HASH_SEED
return base ^ static_cast<uint32_t>(TINT_HASH_SEED);
#endif
return base;
}
};
/// Specialization of HashCombineOffset for size_t == 8.
template <>
struct HashCombineOffset<8> {
/// @returns the seed bias value for HashCombine()
static constexpr inline uint64_t value() {
constexpr uint64_t base = 0x9e3779b97f4a7c16;
#ifdef TINT_HASH_SEED
return base ^ static_cast<uint64_t>(TINT_HASH_SEED);
#endif
return base;
}
};
} // namespace detail
/// Forward declarations (see below)
template <typename... ARGS>
size_t Hash(const ARGS&... values);
template <typename... ARGS>
size_t HashCombine(size_t hash, const ARGS&... values);
/// A STL-compatible hasher that does a more thorough job than most implementations of std::hash.
/// Hasher has been optimized for a better quality hash at the expense of increased computation
/// costs.
template <typename T>
struct Hasher {
/// @param value the value to hash
/// @returns a hash of the value
size_t operator()(const T& value) const { return std::hash<T>()(value); }
};
/// Hasher specialization for pointers
/// std::hash<T*> typically uses a reinterpret of the pointer to a size_t.
/// As most pointers a 4 or 16 byte aligned, this usually results in the LSBs of the hash being 0,
/// resulting in bad hashes for hashtables. This implementation mixes up those LSBs.
template <typename T>
struct Hasher<T*> {
/// @param ptr the pointer to hash
/// @returns a hash of the pointer
size_t operator()(T* ptr) const {
auto hash = std::hash<T*>()(ptr);
#ifdef TINT_HASH_SEED
hash ^= static_cast<uint32_t>(TINT_HASH_SEED);
#endif
return hash ^ (hash >> 4);
}
};
/// Hasher specialization for std::vector
template <typename T>
struct Hasher<std::vector<T>> {
/// @param vector the vector to hash
/// @returns a hash of the vector
size_t operator()(const std::vector<T>& vector) const {
auto hash = Hash(vector.size());
for (auto& el : vector) {
hash = HashCombine(hash, el);
}
return hash;
}
};
/// Hasher specialization for utils::vector
template <typename T, size_t N>
struct Hasher<utils::Vector<T, N>> {
/// @param vector the vector to hash
/// @returns a hash of the vector
size_t operator()(const utils::Vector<T, N>& vector) const {
auto hash = Hash(vector.Length());
for (auto& el : vector) {
hash = HashCombine(hash, el);
}
return hash;
}
};
/// Hasher specialization for std::tuple
template <typename... TYPES>
struct Hasher<std::tuple<TYPES...>> {
/// @param tuple the tuple to hash
/// @returns a hash of the tuple
size_t operator()(const std::tuple<TYPES...>& tuple) const {
return std::apply(Hash<TYPES...>, tuple);
}
};
/// Hasher specialization for std::tuple
template <typename... TYPES>
struct Hasher<std::variant<TYPES...>> {
/// @param variant the variant to hash
/// @returns a hash of the tuple
size_t operator()(const std::variant<TYPES...>& variant) const {
return std::visit([](auto&& val) { return Hash(val); }, variant);
}
};
/// @returns a hash of the variadic list of arguments.
/// The returned hash is dependent on the order of the arguments.
template <typename... ARGS>
size_t Hash(const ARGS&... args) {
if constexpr (sizeof...(ARGS) == 0) {
return 0;
} else if constexpr (sizeof...(ARGS) == 1) {
using T = std::tuple_element_t<0, std::tuple<ARGS...>>;
return Hasher<T>()(args...);
} else {
size_t hash = 102931; // seed with an arbitrary prime
return HashCombine(hash, args...);
}
}
/// @returns a hash of the variadic list of arguments.
/// The returned hash is dependent on the order of the arguments.
template <typename... ARGS>
size_t HashCombine(size_t hash, const ARGS&... values) {
constexpr size_t offset = detail::HashCombineOffset<sizeof(size_t)>::value();
((hash ^= Hash(values) + (offset ^ (hash >> 2))), ...);
return hash;
}
/// Wrapper for a hashable type enabling the wrapped value to be used as a key
/// for an unordered_map or unordered_set.
template <typename T>
struct UnorderedKeyWrapper {
/// The wrapped value
T value;
/// The hash of value
size_t hash;
/// Constructor
/// @param v the value to wrap
explicit UnorderedKeyWrapper(const T& v) : value(v), hash(Hash(v)) {}
/// Move constructor
/// @param v the value to wrap
explicit UnorderedKeyWrapper(T&& v) : value(std::move(v)), hash(Hash(value)) {}
/// @returns true if this wrapper comes before other
/// @param other the RHS of the operator
bool operator<(const UnorderedKeyWrapper& other) const { return hash < other.hash; }
/// @returns true if this wrapped value is equal to the other wrapped value
/// @param other the RHS of the operator
bool operator==(const UnorderedKeyWrapper& other) const { return value == other.value; }
};
} // namespace tint::utils
namespace std {
/// Custom std::hash specialization for tint::utils::UnorderedKeyWrapper
template <typename T>
class hash<tint::utils::UnorderedKeyWrapper<T>> {
public:
/// @param w the UnorderedKeyWrapper
/// @return the hash value
inline std::size_t operator()(const tint::utils::UnorderedKeyWrapper<T>& w) const {
return w.hash;
}
};
} // namespace std
#endif // SRC_TINT_UTILS_HASH_H_