• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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 the Wyhash
16 // algorithm.
17 //
18 // Wyhash is a fast hash function for hash tables, the fastest we've currently
19 // (late 2020) found that passes the SMHasher tests. The algorithm relies on
20 // intrinsic 128-bit multiplication for speed. This is not meant to be secure -
21 // just fast.
22 
23 #ifndef ABSL_HASH_INTERNAL_WYHASH_H_
24 #define ABSL_HASH_INTERNAL_WYHASH_H_
25 
26 #include <stdint.h>
27 #include <stdlib.h>
28 
29 #include "absl/base/config.h"
30 
31 namespace absl {
32 ABSL_NAMESPACE_BEGIN
33 namespace hash_internal {
34 
35 // Hash function for a byte array. A 64-bit seed and a set of five 64-bit
36 // integers are hashed into the result.
37 //
38 // To allow all hashable types (including string_view and Span) to depend on
39 // this algorithm, we keep the API low-level, with as few dependencies as
40 // possible.
41 uint64_t Wyhash(const void* data, size_t len, uint64_t seed,
42                 const uint64_t salt[5]);
43 
44 }  // namespace hash_internal
45 ABSL_NAMESPACE_END
46 }  // namespace absl
47 
48 #endif  // ABSL_HASH_INTERNAL_WYHASH_H_
49