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Diffstat (limited to 'src/rocksdb/util/murmurhash.cc')
| -rw-r--r-- | src/rocksdb/util/murmurhash.cc | 196 |
1 files changed, 196 insertions, 0 deletions
diff --git a/src/rocksdb/util/murmurhash.cc b/src/rocksdb/util/murmurhash.cc new file mode 100644 index 000000000..a69f3918a --- /dev/null +++ b/src/rocksdb/util/murmurhash.cc @@ -0,0 +1,196 @@ +// Copyright (c) 2011-present, Facebook, Inc. All rights reserved. +// This source code is licensed under both the GPLv2 (found in the +// COPYING file in the root directory) and Apache 2.0 License +// (found in the LICENSE.Apache file in the root directory). +// +/* + Murmurhash from http://sites.google.com/site/murmurhash/ + + All code is released to the public domain. For business purposes, Murmurhash + is under the MIT license. +*/ +#include "murmurhash.h" + +#include "port/lang.h" + +#if defined(__x86_64__) + +// ------------------------------------------------------------------- +// +// The same caveats as 32-bit MurmurHash2 apply here - beware of alignment +// and endian-ness issues if used across multiple platforms. +// +// 64-bit hash for 64-bit platforms + +#ifdef ROCKSDB_UBSAN_RUN +#if defined(__clang__) +__attribute__((__no_sanitize__("alignment"))) +#elif defined(__GNUC__) +__attribute__((__no_sanitize_undefined__)) +#endif +#endif +// clang-format off +uint64_t MurmurHash64A ( const void * key, int len, unsigned int seed ) +{ + const uint64_t m = 0xc6a4a7935bd1e995; + const int r = 47; + + uint64_t h = seed ^ (len * m); + + const uint64_t * data = (const uint64_t *)key; + const uint64_t * end = data + (len/8); + + while(data != end) + { + uint64_t k = *data++; + + k *= m; + k ^= k >> r; + k *= m; + + h ^= k; + h *= m; + } + + const unsigned char * data2 = (const unsigned char*)data; + + switch(len & 7) + { + case 7: h ^= ((uint64_t)data2[6]) << 48; FALLTHROUGH_INTENDED; + case 6: h ^= ((uint64_t)data2[5]) << 40; FALLTHROUGH_INTENDED; + case 5: h ^= ((uint64_t)data2[4]) << 32; FALLTHROUGH_INTENDED; + case 4: h ^= ((uint64_t)data2[3]) << 24; FALLTHROUGH_INTENDED; + case 3: h ^= ((uint64_t)data2[2]) << 16; FALLTHROUGH_INTENDED; + case 2: h ^= ((uint64_t)data2[1]) << 8; FALLTHROUGH_INTENDED; + case 1: h ^= ((uint64_t)data2[0]); + h *= m; + }; + + h ^= h >> r; + h *= m; + h ^= h >> r; + + return h; +} +// clang-format on + +#elif defined(__i386__) + +// ------------------------------------------------------------------- +// +// Note - This code makes a few assumptions about how your machine behaves - +// +// 1. We can read a 4-byte value from any address without crashing +// 2. sizeof(int) == 4 +// +// And it has a few limitations - +// +// 1. It will not work incrementally. +// 2. It will not produce the same results on little-endian and big-endian +// machines. +// clang-format off +unsigned int MurmurHash2 ( const void * key, int len, unsigned int seed ) +{ + // 'm' and 'r' are mixing constants generated offline. + // They're not really 'magic', they just happen to work well. + + const unsigned int m = 0x5bd1e995; + const int r = 24; + + // Initialize the hash to a 'random' value + + unsigned int h = seed ^ len; + + // Mix 4 bytes at a time into the hash + + const unsigned char * data = (const unsigned char *)key; + + while(len >= 4) + { + unsigned int k = *(unsigned int *)data; + + k *= m; + k ^= k >> r; + k *= m; + + h *= m; + h ^= k; + + data += 4; + len -= 4; + } + + // Handle the last few bytes of the input array + + switch(len) + { + case 3: h ^= data[2] << 16; FALLTHROUGH_INTENDED; + case 2: h ^= data[1] << 8; FALLTHROUGH_INTENDED; + case 1: h ^= data[0]; + h *= m; + }; + + // Do a few final mixes of the hash to ensure the last few + // bytes are well-incorporated. + + h ^= h >> 13; + h *= m; + h ^= h >> 15; + + return h; +} +// clang-format on + +#else + +// ------------------------------------------------------------------- +// +// Same as MurmurHash2, but endian- and alignment-neutral. +// Half the speed though, alas. +// clang-format off +unsigned int MurmurHashNeutral2 ( const void * key, int len, unsigned int seed ) +{ + const unsigned int m = 0x5bd1e995; + const int r = 24; + + unsigned int h = seed ^ len; + + const unsigned char * data = (const unsigned char *)key; + + while(len >= 4) + { + unsigned int k; + + k = data[0]; + k |= data[1] << 8; + k |= data[2] << 16; + k |= data[3] << 24; + + k *= m; + k ^= k >> r; + k *= m; + + h *= m; + h ^= k; + + data += 4; + len -= 4; + } + + switch(len) + { + case 3: h ^= data[2] << 16; FALLTHROUGH_INTENDED; + case 2: h ^= data[1] << 8; FALLTHROUGH_INTENDED; + case 1: h ^= data[0]; + h *= m; + }; + + h ^= h >> 13; + h *= m; + h ^= h >> 15; + + return h; +} +// clang-format on + +#endif |