104 lines
2.9 KiB
C++
104 lines
2.9 KiB
C++
/*
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* Copyright (C) 2018 The Android Open Source Project
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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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*/
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#ifndef TNT_UTILS_HASH_H
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#define TNT_UTILS_HASH_H
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#include <functional> // for std::hash
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#include <stdint.h>
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#include <stddef.h>
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namespace utils::hash {
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// Hash function that takes an arbitrary swath of word-aligned data.
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inline uint32_t murmur3(const uint32_t* key, size_t wordCount, uint32_t seed) noexcept {
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uint32_t h = seed;
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size_t i = wordCount;
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do {
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uint32_t k = *key++;
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k *= 0xcc9e2d51u;
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k = (k << 15u) | (k >> 17u);
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k *= 0x1b873593u;
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h ^= k;
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h = (h << 13u) | (h >> 19u);
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h = (h * 5u) + 0xe6546b64u;
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} while (--i);
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h ^= wordCount;
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h ^= h >> 16u;
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h *= 0x85ebca6bu;
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h ^= h >> 13u;
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h *= 0xc2b2ae35u;
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h ^= h >> 16u;
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return h;
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}
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// The hash yields the same result for a given byte sequence regardless of alignment.
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inline uint32_t murmurSlow(const uint8_t* key, size_t byteCount, uint32_t seed) noexcept {
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const size_t wordCount = (byteCount + 3) / 4;
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const uint8_t* const last = key + byteCount;
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// The remainder is identical to murmur3() except an inner loop safely "reads" an entire word.
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uint32_t h = seed;
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size_t i = wordCount;
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do {
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uint32_t k = 0;
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for (int i = 0; i < 4 && key < last; ++i, ++key) {
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k >>= 8;
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k |= uint32_t(*key) << 24;
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}
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k *= 0xcc9e2d51u;
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k = (k << 15u) | (k >> 17u);
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k *= 0x1b873593u;
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h ^= k;
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h = (h << 13u) | (h >> 19u);
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h = (h * 5u) + 0xe6546b64u;
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} while (--i);
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h ^= wordCount;
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h ^= h >> 16u;
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h *= 0x85ebca6bu;
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h ^= h >> 13u;
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h *= 0xc2b2ae35u;
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h ^= h >> 16u;
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return h;
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}
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template<typename T>
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struct MurmurHashFn {
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uint32_t operator()(const T& key) const noexcept {
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static_assert(0 == (sizeof(key) & 3u), "Hashing requires a size that is a multiple of 4.");
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return murmur3((const uint32_t*) &key, sizeof(key) / 4, 0);
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}
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};
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// combines two hashes together
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template<class T>
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inline void combine(size_t& seed, const T& v) noexcept {
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std::hash<T> hasher;
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seed ^= hasher(v) + 0x9e3779b9u + (seed << 6u) + (seed >> 2u);
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}
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// combines two hashes together, faster but less good
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template<class T>
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inline void combine_fast(size_t& seed, const T& v) noexcept {
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std::hash<T> hasher;
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seed ^= hasher(v) << 1u;
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}
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} // namespace utils::hash
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#endif // TNT_UTILS_HASH_H
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