| // SPDX-FileCopyrightText: 2011 Google, Inc. | |
| // SPDX-FileContributor: Geoff Pike | |
| // SPDX-FileContributor: Jyrki Alakuijala | |
| // SPDX-License-Identifier: MIT | |
| // CityHash, by Geoff Pike and Jyrki Alakuijala | |
| // | |
| // http://code.google.com/p/cityhash/ | |
| // | |
| // This file provides a few functions for hashing strings. All of them are | |
| // high-quality functions in the sense that they pass standard tests such | |
| // as Austin Appleby's SMHasher. They are also fast. | |
| // | |
| // For 64-bit x86 code, on short strings, we don't know of anything faster than | |
| // CityHash64 that is of comparable quality. We believe our nearest competitor | |
| // is Murmur3. For 64-bit x86 code, CityHash64 is an excellent choice for hash | |
| // tables and most other hashing (excluding cryptography). | |
| // | |
| // For 64-bit x86 code, on long strings, the picture is more complicated. | |
| // On many recent Intel CPUs, such as Nehalem, Westmere, Sandy Bridge, etc., | |
| // CityHashCrc128 appears to be faster than all competitors of comparable | |
| // quality. CityHash128 is also good but not quite as fast. We believe our | |
| // nearest competitor is Bob Jenkins' Spooky. We don't have great data for | |
| // other 64-bit CPUs, but for long strings we know that Spooky is slightly | |
| // faster than CityHash on some relatively recent AMD x86-64 CPUs, for example. | |
| // Note that CityHashCrc128 is declared in citycrc.h. | |
| // | |
| // For 32-bit x86 code, we don't know of anything faster than CityHash32 that | |
| // is of comparable quality. We believe our nearest competitor is Murmur3A. | |
| // (On 64-bit CPUs, it is typically faster to use the other CityHash variants.) | |
| // | |
| // Functions in the CityHash family are not suitable for cryptography. | |
| // | |
| // Please see CityHash's README file for more details on our performance | |
| // measurements and so on. | |
| // | |
| // WARNING: This code has been only lightly tested on big-endian platforms! | |
| // It is known to work well on little-endian platforms that have a small penalty | |
| // for unaligned reads, such as current Intel and AMD moderate-to-high-end CPUs. | |
| // It should work on all 32-bit and 64-bit platforms that allow unaligned reads; | |
| // bug reports are welcome. | |
| // | |
| // By the way, for some hash functions, given strings a and b, the hash | |
| // of a+b is easily derived from the hashes of a and b. This property | |
| // doesn't hold for any hash functions in this file. | |
| namespace Common { | |
| // Hash function for a byte array. | |
| [[nodiscard]] u64 CityHash64(const char* buf, size_t len); | |
| // Hash function for a byte array. For convenience, a 64-bit seed is also | |
| // hashed into the result. | |
| [[nodiscard]] u64 CityHash64WithSeed(const char* buf, size_t len, u64 seed); | |
| // Hash function for a byte array. For convenience, two seeds are also | |
| // hashed into the result. | |
| [[nodiscard]] u64 CityHash64WithSeeds(const char* buf, size_t len, u64 seed0, u64 seed1); | |
| // Hash function for a byte array. | |
| [[nodiscard]] u128 CityHash128(const char* s, size_t len); | |
| // Hash function for a byte array. For convenience, a 128-bit seed is also | |
| // hashed into the result. | |
| [[nodiscard]] u128 CityHash128WithSeed(const char* s, size_t len, u128 seed); | |
| // Hash 128 input bits down to 64 bits of output. | |
| // This is intended to be a reasonably good hash function. | |
| [[nodiscard]] inline u64 Hash128to64(const u128& x) { | |
| // Murmur-inspired hashing. | |
| const u64 mul = 0x9ddfea08eb382d69ULL; | |
| u64 a = (x[0] ^ x[1]) * mul; | |
| a ^= (a >> 47); | |
| u64 b = (x[1] ^ a) * mul; | |
| b ^= (b >> 47); | |
| b *= mul; | |
| return b; | |
| } | |
| } // namespace Common | |