1 // Copyright 2014 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #include "base/hash.h" 6 7 #include <functional> 8 SuperFastHash(const char * data,size_t len)9 uint32_t SuperFastHash(const char* data, size_t len) { 10 std::hash<std::string> hash_fn; 11 return hash_fn(std::string(data, len)); 12 } 13 14 namespace base { 15 Hash(const void * data,size_t length)16 uint32_t Hash(const void* data, size_t length) { 17 // Currently our in-memory hash is the same as the persistent hash. The 18 // split between in-memory and persistent hash functions is maintained to 19 // allow the in-memory hash function to be updated in the future. 20 return PersistentHash(data, length); 21 } 22 Hash(const std::string & str)23 uint32_t Hash(const std::string& str) { 24 return PersistentHash(str.data(), str.size()); 25 } 26 Hash(const string16 & str)27 uint32_t Hash(const string16& str) { 28 return PersistentHash(str.data(), str.size() * sizeof(char16)); 29 } 30 PersistentHash(const void * data,size_t length)31 uint32_t PersistentHash(const void* data, size_t length) { 32 // This hash function must not change, since it is designed to be persistable 33 // to disk. 34 if (length > static_cast<size_t>(std::numeric_limits<int>::max())) { 35 NOTREACHED(); 36 return 0; 37 } 38 return ::SuperFastHash(reinterpret_cast<const char*>(data), 39 static_cast<int>(length)); 40 } 41 PersistentHash(const std::string & str)42 uint32_t PersistentHash(const std::string& str) { 43 return PersistentHash(str.data(), str.size()); 44 } 45 46 // Implement hashing for pairs of at-most 32 bit integer values. 47 // When size_t is 32 bits, we turn the 64-bit hash code into 32 bits by using 48 // multiply-add hashing. This algorithm, as described in 49 // Theorem 4.3.3 of the thesis "Über die Komplexität der Multiplikation in 50 // eingeschränkten Branchingprogrammmodellen" by Woelfel, is: 51 // 52 // h32(x32, y32) = (h64(x32, y32) * rand_odd64 + rand16 * 2^16) % 2^64 / 2^32 53 // 54 // Contact danakj@chromium.org for any questions. HashInts32(uint32_t value1,uint32_t value2)55 size_t HashInts32(uint32_t value1, uint32_t value2) { 56 uint64_t value1_64 = value1; 57 uint64_t hash64 = (value1_64 << 32) | value2; 58 59 if (sizeof(size_t) >= sizeof(uint64_t)) 60 return static_cast<size_t>(hash64); 61 62 uint64_t odd_random = 481046412LL << 32 | 1025306955LL; 63 uint32_t shift_random = 10121U << 16; 64 65 hash64 = hash64 * odd_random + shift_random; 66 size_t high_bits = 67 static_cast<size_t>(hash64 >> (8 * (sizeof(uint64_t) - sizeof(size_t)))); 68 return high_bits; 69 } 70 71 // Implement hashing for pairs of up-to 64-bit integer values. 72 // We use the compound integer hash method to produce a 64-bit hash code, by 73 // breaking the two 64-bit inputs into 4 32-bit values: 74 // http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000 75 // Then we reduce our result to 32 bits if required, similar to above. HashInts64(uint64_t value1,uint64_t value2)76 size_t HashInts64(uint64_t value1, uint64_t value2) { 77 uint32_t short_random1 = 842304669U; 78 uint32_t short_random2 = 619063811U; 79 uint32_t short_random3 = 937041849U; 80 uint32_t short_random4 = 3309708029U; 81 82 uint32_t value1a = static_cast<uint32_t>(value1 & 0xffffffff); 83 uint32_t value1b = static_cast<uint32_t>((value1 >> 32) & 0xffffffff); 84 uint32_t value2a = static_cast<uint32_t>(value2 & 0xffffffff); 85 uint32_t value2b = static_cast<uint32_t>((value2 >> 32) & 0xffffffff); 86 87 uint64_t product1 = static_cast<uint64_t>(value1a) * short_random1; 88 uint64_t product2 = static_cast<uint64_t>(value1b) * short_random2; 89 uint64_t product3 = static_cast<uint64_t>(value2a) * short_random3; 90 uint64_t product4 = static_cast<uint64_t>(value2b) * short_random4; 91 92 uint64_t hash64 = product1 + product2 + product3 + product4; 93 94 if (sizeof(size_t) >= sizeof(uint64_t)) 95 return static_cast<size_t>(hash64); 96 97 uint64_t odd_random = 1578233944LL << 32 | 194370989LL; 98 uint32_t shift_random = 20591U << 16; 99 100 hash64 = hash64 * odd_random + shift_random; 101 size_t high_bits = 102 static_cast<size_t>(hash64 >> (8 * (sizeof(uint64_t) - sizeof(size_t)))); 103 return high_bits; 104 } 105 106 } // namespace base 107