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
17namespace absl {
18ABSL_NAMESPACE_BEGIN
19namespace hash_internal {
20
21uint64_t MixingHashState::CombineLargeContiguousImpl32(
22 uint64_t state, const unsigned char* first, size_t len) {
23 while (len >= PiecewiseChunkSize()) {
24 state = Mix(state,
25 v: hash_internal::CityHash32(s: reinterpret_cast<const char*>(first),
26 len: 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
35uint64_t MixingHashState::CombineLargeContiguousImpl64(
36 uint64_t state, const unsigned char* first, size_t len) {
37 while (len >= PiecewiseChunkSize()) {
38 state = Mix(state, v: Hash64(data: first, len: 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
47ABSL_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
56constexpr uint64_t kHashSalt[5] = {
57 uint64_t{0x243F6A8885A308D3}, uint64_t{0x13198A2E03707344},
58 uint64_t{0xA4093822299F31D0}, uint64_t{0x082EFA98EC4E6C89},
59 uint64_t{0x452821E638D01377},
60};
61
62uint64_t MixingHashState::LowLevelHashImpl(const unsigned char* data,
63 size_t len) {
64 return LowLevelHash(data, len, seed: Seed(), salt: kHashSalt);
65}
66
67} // namespace hash_internal
68ABSL_NAMESPACE_END
69} // namespace absl
70

source code of flutter_engine/third_party/abseil-cpp/absl/hash/internal/hash.cc