low_level_hash.h (1844B)
1 // Copyright 2020 The Abseil Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 // 15 // This file provides the Google-internal implementation of LowLevelHash. 16 // 17 // LowLevelHash is a fast hash function for hash tables, the fastest we've 18 // currently (late 2020) found that passes the SMHasher tests. The algorithm 19 // relies on intrinsic 128-bit multiplication for speed. This is not meant to be 20 // secure - just fast. 21 // 22 // It is closely based on a version of wyhash, but does not maintain or 23 // guarantee future compatibility with it. 24 25 #ifndef ABSL_HASH_INTERNAL_LOW_LEVEL_HASH_H_ 26 #define ABSL_HASH_INTERNAL_LOW_LEVEL_HASH_H_ 27 28 #include <stdint.h> 29 #include <stdlib.h> 30 31 #include "absl/base/config.h" 32 33 namespace absl { 34 ABSL_NAMESPACE_BEGIN 35 namespace hash_internal { 36 37 // Hash function for a byte array. A 64-bit seed and a set of five 64-bit 38 // integers are hashed into the result. The length must be greater than 32. 39 // 40 // To allow all hashable types (including string_view and Span) to depend on 41 // this algorithm, we keep the API low-level, with as few dependencies as 42 // possible. 43 uint64_t LowLevelHashLenGt32(const void* data, size_t len, uint64_t seed, 44 const uint64_t salt[5]); 45 46 } // namespace hash_internal 47 ABSL_NAMESPACE_END 48 } // namespace absl 49 50 #endif // ABSL_HASH_INTERNAL_LOW_LEVEL_HASH_H_