1 // Copyright 2018 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 #include "absl/hash/internal/hash.h"
16
17 namespace absl {
18 ABSL_NAMESPACE_BEGIN
19 namespace hash_internal {
20
CombineLargeContiguousImpl32(uint64_t state,const unsigned char * first,size_t len)21 uint64_t MixingHashState::CombineLargeContiguousImpl32(
22 uint64_t state, const unsigned char* first, size_t len) {
23 while (len >= PiecewiseChunkSize()) {
24 state = Mix(state,
25 hash_internal::CityHash32(reinterpret_cast<const char*>(first),
26 PiecewiseChunkSize()));
27 len -= PiecewiseChunkSize();
28 first += PiecewiseChunkSize();
29 }
30 // Handle the remainder.
31 return CombineContiguousImpl(state, first, len,
32 std::integral_constant<int, 4>{});
33 }
34
CombineLargeContiguousImpl64(uint64_t state,const unsigned char * first,size_t len)35 uint64_t MixingHashState::CombineLargeContiguousImpl64(
36 uint64_t state, const unsigned char* first, size_t len) {
37 while (len >= PiecewiseChunkSize()) {
38 state = Mix(state, Hash64(first, PiecewiseChunkSize()));
39 len -= PiecewiseChunkSize();
40 first += PiecewiseChunkSize();
41 }
42 // Handle the remainder.
43 return CombineContiguousImpl(state, first, len,
44 std::integral_constant<int, 8>{});
45 }
46
47 ABSL_CONST_INIT const void* const MixingHashState::kSeed = &kSeed;
48
49 // The salt array used by LowLevelHash. This array is NOT the mechanism used to
50 // make absl::Hash non-deterministic between program invocations. See `Seed()`
51 // for that mechanism.
52 //
53 // Any random values are fine. These values are just digits from the decimal
54 // part of pi.
55 // https://en.wikipedia.org/wiki/Nothing-up-my-sleeve_number
56 constexpr uint64_t kHashSalt[5] = {
57 uint64_t{0x243F6A8885A308D3}, uint64_t{0x13198A2E03707344},
58 uint64_t{0xA4093822299F31D0}, uint64_t{0x082EFA98EC4E6C89},
59 uint64_t{0x452821E638D01377},
60 };
61
LowLevelHashImpl(const unsigned char * data,size_t len)62 uint64_t MixingHashState::LowLevelHashImpl(const unsigned char* data,
63 size_t len) {
64 return LowLevelHashLenGt16(data, len, Seed(), kHashSalt);
65 }
66
67 } // namespace hash_internal
68 ABSL_NAMESPACE_END
69 } // namespace absl
70