| // Copyright 2020 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef UTIL_HASHING_H_ |
| #define UTIL_HASHING_H_ |
| |
| namespace openscreen { |
| |
| // Computes the aggregate hash of the provided hashable objects. |
| // Seed must initially use a large prime between 2^63 and 2^64 as a starting |
| // value, or the result of a previous call to this function. |
| template <typename... T> |
| uint64_t ComputeAggregateHash(uint64_t seed, const T&... objs) { |
| auto hash_combiner = [](uint64_t seed, uint64_t hash_value) -> uint64_t { |
| static const uint64_t kMultiplier = UINT64_C(0x9ddfea08eb382d69); |
| uint64_t a = (hash_value ^ seed) * kMultiplier; |
| a ^= (a >> 47); |
| uint64_t b = (seed ^ a) * kMultiplier; |
| b ^= (b >> 47); |
| b *= kMultiplier; |
| return b; |
| }; |
| |
| uint64_t result = seed; |
| std::vector<uint64_t> hashes{std::hash<T>()(objs)...}; |
| for (uint64_t hash : hashes) { |
| result = hash_combiner(result, hash); |
| } |
| return result; |
| } |
| |
| template <typename... T> |
| uint64_t ComputeAggregateHash(const T&... objs) { |
| // This value is taken from absl::Hash implementation. |
| constexpr uint64_t default_seed = UINT64_C(0xc3a5c85c97cb3127); |
| return ComputeAggregateHash(default_seed, objs...); |
| } |
| |
| struct PairHash { |
| template <typename TFirst, typename TSecond> |
| size_t operator()(const std::pair<TFirst, TSecond>& pair) const { |
| return ComputeAggregateHash(pair.first, pair.second); |
| } |
| }; |
| |
| } // namespace openscreen |
| |
| #endif // UTIL_HASHING_H_ |