75 lines
2.3 KiB
C
75 lines
2.3 KiB
C
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// Copyright 2021 The Tint Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef SRC_UTILS_HASH_H_
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#define SRC_UTILS_HASH_H_
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#include <stdint.h>
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#include <cstdio>
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#include <functional>
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namespace tint {
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namespace utils {
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namespace detail {
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/// Helper for obtaining a seed bias value for HashCombine with a bit-width
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/// dependent on the size of size_t.
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template <int SIZE_OF_SIZE_T>
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struct HashCombineOffset {};
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/// Specialization of HashCombineOffset for size_t == 4.
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template <>
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struct HashCombineOffset<4> {
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/// @returns the seed bias value for HashCombine()
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static constexpr inline uint32_t value() { return 0x7f4a7c16; }
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};
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/// Specialization of HashCombineOffset for size_t == 8.
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template <>
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struct HashCombineOffset<8> {
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/// @returns the seed bias value for HashCombine()
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static constexpr inline uint64_t value() { return 0x9e3779b97f4a7c16; }
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};
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// When hashing sparse structures we want to iteratively build a hash value with
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// only parts of the data. HashCombine "hashes" together an existing hash and
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// hashable values.
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template <typename T>
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void HashCombine(size_t* hash, const T& value) {
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constexpr size_t offset = HashCombineOffset<sizeof(size_t)>::value();
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*hash ^= std::hash<T>()(value) + offset + (*hash << 6) + (*hash >> 2);
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}
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template <typename T, typename... ARGS>
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void HashCombine(size_t* hash, const T& value, const ARGS&... args) {
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HashCombine(hash, value);
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HashCombine(hash, args...);
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}
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} // namespace detail
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/// @returns a hash of the combined arguments. The returned hash is dependent on
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/// the order of the arguments.
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template <typename... ARGS>
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size_t Hash(const ARGS&... args) {
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size_t hash = 102931; // seed with an arbitrary prime
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detail::HashCombine(&hash, args...);
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return hash;
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}
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} // namespace utils
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} // namespace tint
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#endif // SRC_UTILS_HASH_H_
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