| /* |
| * Copyright 2015 WebAssembly Community Group participants |
| * |
| * 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 wasm_support_hash_h |
| #define wasm_support_hash_h |
| |
| #include <functional> |
| #include <stdint.h> |
| |
| namespace wasm { |
| |
| // Computes the digest of `value`. |
| template<typename T> inline std::size_t hash(const T& value) { |
| return std::hash<T>{}(value); |
| } |
| |
| // Combines two digests into the first digest. Use instead of `rehash` if |
| // `otherDigest` is another digest and not a `size_t` value. |
| static inline void hash_combine(std::size_t& digest, std::size_t otherDigest) { |
| // see: boost/container_hash/hash.hpp |
| // The constant is the N-bits reciprocal of the golden ratio: |
| // phi = (1 + sqrt(5)) / 2 |
| #if SIZE_MAX == UINT64_MAX |
| // trunc(2^64 / phi) = 0x9e3779b97f4a7c15 |
| digest ^= otherDigest + 0x9e3779b97f4a7c15 + (digest << 12) + (digest >> 4); |
| #else |
| // trunc(2^32 / phi) = 0x9e3779b9 |
| digest ^= otherDigest + 0x9e3779b9 + (digest << 6) + (digest >> 2); |
| #endif |
| } |
| |
| // Hashes `value` and combines the resulting digest into the existing digest. |
| // Use instead of `hash_combine` if `value` is not another digest. |
| template<typename T> inline void rehash(std::size_t& digest, const T& value) { |
| hash_combine(digest, hash(value)); |
| } |
| |
| } // namespace wasm |
| |
| #endif // wasm_support_hash_h |