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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 <vector>
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() { return 0x7f4a7c16; }
};
/// Specialization of HashCombineOffset for size_t == 8.
template <>
struct HashCombineOffset<8> {
/// @returns the seed bias value for HashCombine()
static constexpr inline uint64_t value() { return 0x9e3779b97f4a7c16; }
};
} // namespace detail
/// HashCombine "hashes" together an existing hash and hashable values.
template <typename T>
void HashCombine(size_t* hash, const T& value) {
constexpr size_t offset = detail::HashCombineOffset<sizeof(size_t)>::value();
*hash ^= std::hash<T>()(value) + offset + (*hash << 6) + (*hash >> 2);
}
/// HashCombine "hashes" together an existing hash and hashable values.
template <typename T>
void HashCombine(size_t* hash, const std::vector<T>& vector) {
HashCombine(hash, vector.size());
for (auto& el : vector) {
HashCombine(hash, el);
}
}
/// HashCombine "hashes" together an existing hash and hashable values.
template <typename T, typename... ARGS>
void HashCombine(size_t* hash, const T& value, const ARGS&... args) {
HashCombine(hash, value);
HashCombine(hash, args...);
}
/// @returns a hash of the combined arguments. The returned hash is dependent on
/// the order of the arguments.
template <typename... ARGS>
size_t Hash(const ARGS&... args) {
size_t hash = 102931; // seed with an arbitrary prime
HashCombine(&hash, args...);
return hash;
}
} // namespace tint::utils
#endif // SRC_TINT_UTILS_HASH_H_