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105 lines
4.1 KiB
C++
105 lines
4.1 KiB
C++
// Copyright (c) 2011 Google, Inc.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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//
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// CityHash, by Geoff Pike and Jyrki Alakuijala
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//
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// This file provides a few functions for hashing strings. On x86-64
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// hardware in 2011, CityHash64() is faster than other high-quality
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// hash functions, such as Murmur. This is largely due to higher
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// instruction-level parallelism. CityHash64() and CityHash128() also perform
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// well on hash-quality tests.
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//
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// CityHash128() is optimized for relatively long strings and returns
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// a 128-bit hash. For strings more than about 2000 bytes it can be
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// faster than CityHash64().
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//
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// Functions in the CityHash family are not suitable for cryptography.
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//
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// WARNING: This code has not been tested on big-endian platforms!
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// It is known to work well on little-endian platforms that have a small penalty
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// for unaligned reads, such as current Intel and AMD moderate-to-high-end CPUs.
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//
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// By the way, for some hash functions, given strings a and b, the hash
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// of a+b is easily derived from the hashes of a and b. This property
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// doesn't hold for any hash functions in this file.
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#ifndef CITY_HASH_H_
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#define CITY_HASH_H_
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#include <stdlib.h> // for size_t.
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#include <stdint.h>
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#include <utility>
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/** This is a version of CityHash that predates v1.0.3 algorithm change.
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* Why we need exactly this version?
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* Although hash values of CityHash are not recommended for storing persistently anywhere,
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* it has already been used this way in ClickHouse:
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* - for calculation of checksums of compressed chunks and for data parts;
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* - this version of CityHash is exposed in cityHash64 function in ClickHouse SQL language;
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* - and already used by many users for data ordering, sampling and sharding.
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*/
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namespace CityHash_v1_0_2
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{
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typedef uint8_t uint8;
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typedef uint32_t uint32;
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typedef uint64_t uint64;
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typedef std::pair<uint64, uint64> uint128;
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inline uint64 Uint128Low64(const uint128& x) { return x.first; }
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inline uint64 Uint128High64(const uint128& x) { return x.second; }
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// Hash function for a byte array.
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uint64 CityHash64(const char *buf, size_t len);
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// Hash function for a byte array. For convenience, a 64-bit seed is also
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// hashed into the result.
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uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed);
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// Hash function for a byte array. For convenience, two seeds are also
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// hashed into the result.
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uint64 CityHash64WithSeeds(const char *buf, size_t len,
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uint64 seed0, uint64 seed1);
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// Hash function for a byte array.
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uint128 CityHash128(const char *s, size_t len);
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// Hash function for a byte array. For convenience, a 128-bit seed is also
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// hashed into the result.
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uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed);
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// Hash 128 input bits down to 64 bits of output.
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// This is intended to be a reasonably good hash function.
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inline uint64 Hash128to64(const uint128& x) {
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// Murmur-inspired hashing.
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const uint64 kMul = 0x9ddfea08eb382d69ULL;
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uint64 a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul;
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a ^= (a >> 47);
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uint64 b = (Uint128High64(x) ^ a) * kMul;
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b ^= (b >> 47);
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b *= kMul;
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return b;
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}
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}
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#endif // CITY_HASH_H_
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