| // Copyright 2020 The Abseil 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 | |
| // | |
| // https://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. | |
| // | |
| // This file provides the Google-internal implementation of LowLevelHash. | |
| // | |
| // LowLevelHash is a fast hash function for hash tables, the fastest we've | |
| // currently (late 2020) found that passes the SMHasher tests. The algorithm | |
| // relies on intrinsic 128-bit multiplication for speed. This is not meant to be | |
| // secure - just fast. | |
| // | |
| // It is closely based on a version of wyhash, but does not maintain or | |
| // guarantee future compatibility with it. | |
| namespace absl { | |
| ABSL_NAMESPACE_BEGIN | |
| namespace hash_internal { | |
| // Hash function for a byte array. A 64-bit seed and a set of five 64-bit | |
| // integers are hashed into the result. | |
| // | |
| // To allow all hashable types (including string_view and Span) to depend on | |
| // this algorithm, we keep the API low-level, with as few dependencies as | |
| // possible. | |
| uint64_t LowLevelHash(const void* data, size_t len, uint64_t seed, | |
| const uint64_t salt[5]); | |
| } // namespace hash_internal | |
| ABSL_NAMESPACE_END | |
| } // namespace absl | |