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112 lines
4.8 KiB
112 lines
4.8 KiB
// 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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// http://code.google.com/p/cityhash/ |
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// |
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// This file provides a few functions for hashing strings. All of them are |
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// high-quality functions in the sense that they pass standard tests such |
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// as Austin Appleby's SMHasher. They are also fast. |
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// |
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// For 64-bit x86 code, on short strings, we don't know of anything faster than |
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// CityHash64 that is of comparable quality. We believe our nearest competitor |
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// is Murmur3. For 64-bit x86 code, CityHash64 is an excellent choice for hash |
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// tables and most other hashing (excluding cryptography). |
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// |
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// For 64-bit x86 code, on long strings, the picture is more complicated. |
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// On many recent Intel CPUs, such as Nehalem, Westmere, Sandy Bridge, etc., |
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// CityHashCrc128 appears to be faster than all competitors of comparable |
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// quality. CityHash128 is also good but not quite as fast. We believe our |
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// nearest competitor is Bob Jenkins' Spooky. We don't have great data for |
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// other 64-bit CPUs, but for long strings we know that Spooky is slightly |
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// faster than CityHash on some relatively recent AMD x86-64 CPUs, for example. |
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// Note that CityHashCrc128 is declared in citycrc.h. |
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// |
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// For 32-bit x86 code, we don't know of anything faster than CityHash32 that |
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// is of comparable quality. We believe our nearest competitor is Murmur3A. |
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// (On 64-bit CPUs, it is typically faster to use the other CityHash variants.) |
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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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// Please see CityHash's README file for more details on our performance |
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// measurements and so on. |
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// |
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// WARNING: This code has been only lightly 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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// It should work on all 32-bit and 64-bit platforms that allow unaligned reads; |
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// bug reports are welcome. |
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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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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 function for a byte array. Most useful in 32-bit binaries. |
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uint32 CityHash32(const char *buf, size_t len); |
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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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#endif // CITY_HASH_H_
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