Yangster-mac | 9def8e3 | 2018-04-17 13:55:51 -0700 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright (C) 2017 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | #include "hash.h" |
| 18 | |
| 19 | namespace android { |
| 20 | namespace os { |
| 21 | namespace statsd { |
| 22 | |
| 23 | namespace { |
| 24 | // Lower-level versions of Get... that read directly from a character buffer |
| 25 | // without any bounds checking. |
| 26 | inline uint32_t DecodeFixed32(const char *ptr) { |
| 27 | return ((static_cast<uint32_t>(static_cast<unsigned char>(ptr[0]))) | |
| 28 | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[1])) << 8) | |
| 29 | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[2])) << 16) | |
| 30 | (static_cast<uint32_t>(static_cast<unsigned char>(ptr[3])) << 24)); |
| 31 | } |
| 32 | |
| 33 | inline uint64_t DecodeFixed64(const char* ptr) { |
| 34 | uint64_t lo = DecodeFixed32(ptr); |
| 35 | uint64_t hi = DecodeFixed32(ptr + 4); |
| 36 | return (hi << 32) | lo; |
| 37 | } |
| 38 | |
| 39 | // 0xff is in case char is signed. |
| 40 | static inline uint32_t ByteAs32(char c) { return static_cast<uint32_t>(c) & 0xff; } |
| 41 | static inline uint64_t ByteAs64(char c) { return static_cast<uint64_t>(c) & 0xff; } |
| 42 | |
| 43 | } // namespace |
| 44 | |
| 45 | uint32_t Hash32(const char *data, size_t n, uint32_t seed) { |
| 46 | // 'm' and 'r' are mixing constants generated offline. |
| 47 | // They're not really 'magic', they just happen to work well. |
| 48 | const uint32_t m = 0x5bd1e995; |
| 49 | const int r = 24; |
| 50 | |
| 51 | // Initialize the hash to a 'random' value |
| 52 | uint32_t h = static_cast<uint32_t>(seed ^ n); |
| 53 | |
| 54 | // Mix 4 bytes at a time into the hash |
| 55 | while (n >= 4) { |
| 56 | uint32_t k = DecodeFixed32(data); |
| 57 | k *= m; |
| 58 | k ^= k >> r; |
| 59 | k *= m; |
| 60 | h *= m; |
| 61 | h ^= k; |
| 62 | data += 4; |
| 63 | n -= 4; |
| 64 | } |
| 65 | |
| 66 | // Handle the last few bytes of the input array |
| 67 | switch (n) { |
| 68 | case 3: |
| 69 | h ^= ByteAs32(data[2]) << 16; |
| 70 | case 2: |
| 71 | h ^= ByteAs32(data[1]) << 8; |
| 72 | case 1: |
| 73 | h ^= ByteAs32(data[0]); |
| 74 | h *= m; |
| 75 | } |
| 76 | |
| 77 | // Do a few final mixes of the hash to ensure the last few |
| 78 | // bytes are well-incorporated. |
| 79 | h ^= h >> 13; |
| 80 | h *= m; |
| 81 | h ^= h >> 15; |
| 82 | return h; |
| 83 | } |
| 84 | |
| 85 | uint64_t Hash64(const char* data, size_t n, uint64_t seed) { |
| 86 | const uint64_t m = 0xc6a4a7935bd1e995; |
| 87 | const int r = 47; |
| 88 | |
| 89 | uint64_t h = seed ^ (n * m); |
| 90 | |
| 91 | while (n >= 8) { |
| 92 | uint64_t k = DecodeFixed64(data); |
| 93 | data += 8; |
| 94 | n -= 8; |
| 95 | |
| 96 | k *= m; |
| 97 | k ^= k >> r; |
| 98 | k *= m; |
| 99 | |
| 100 | h ^= k; |
| 101 | h *= m; |
| 102 | } |
| 103 | |
| 104 | switch (n) { |
| 105 | case 7: |
| 106 | h ^= ByteAs64(data[6]) << 48; |
| 107 | case 6: |
| 108 | h ^= ByteAs64(data[5]) << 40; |
| 109 | case 5: |
| 110 | h ^= ByteAs64(data[4]) << 32; |
| 111 | case 4: |
| 112 | h ^= ByteAs64(data[3]) << 24; |
| 113 | case 3: |
| 114 | h ^= ByteAs64(data[2]) << 16; |
| 115 | case 2: |
| 116 | h ^= ByteAs64(data[1]) << 8; |
| 117 | case 1: |
| 118 | h ^= ByteAs64(data[0]); |
| 119 | h *= m; |
| 120 | } |
| 121 | |
| 122 | h ^= h >> r; |
| 123 | h *= m; |
| 124 | h ^= h >> r; |
| 125 | |
| 126 | return h; |
| 127 | } |
| 128 | } // namespace statsd |
| 129 | } // namespace os |
| 130 | } // namespace android |