From 48cd2c3f351ff188bc85684b84a91b6e6d17d896 Mon Sep 17 00:00:00 2001 From: Abseil Team Date: Thu, 27 Sep 2018 12:24:54 -0700 Subject: Export of internal Abseil changes. -- 4eacae3ff1b14b1d309e8092185bc10e8a6203cf by Derek Mauro : Release SwissTable - a fast, efficient, cache-friendly hash table. https://www.youtube.com/watch?v=ncHmEUmJZf4 PiperOrigin-RevId: 214816527 -- df8c3dfab3cfb2f4365909a84d0683b193cfbb11 by Derek Mauro : Internal change PiperOrigin-RevId: 214785288 -- 1eabd5266bbcebc33eecc91e5309b751856a75c8 by Abseil Team : Internal change PiperOrigin-RevId: 214722931 -- 2ebbfac950f83146b46253038e7dd7dcde9f2951 by Derek Mauro : Internal change PiperOrigin-RevId: 214701684 GitOrigin-RevId: 4eacae3ff1b14b1d309e8092185bc10e8a6203cf Change-Id: I9ba64e395b22ad7863213d157b8019b082adc19d --- absl/hash/internal/city.h | 108 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 108 insertions(+) create mode 100644 absl/hash/internal/city.h (limited to 'absl/hash/internal/city.h') diff --git a/absl/hash/internal/city.h b/absl/hash/internal/city.h new file mode 100644 index 00000000..55b37b87 --- /dev/null +++ b/absl/hash/internal/city.h @@ -0,0 +1,108 @@ +// Copyright 2018 The Abseil Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. +// +// 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. + +#ifndef ABSL_HASH_INTERNAL_CITY_H_ +#define ABSL_HASH_INTERNAL_CITY_H_ + +#include +#include // for size_t. +#include + + +namespace absl { +namespace hash_internal { + +typedef std::pair uint128; + +inline uint64_t Uint128Low64(const uint128 &x) { return x.first; } +inline uint64_t Uint128High64(const uint128 &x) { return x.second; } + +// Hash function for a byte array. +uint64_t CityHash64(const char *s, size_t len); + +// Hash function for a byte array. For convenience, a 64-bit seed is also +// hashed into the result. +uint64_t CityHash64WithSeed(const char *s, size_t len, uint64_t seed); + +// Hash function for a byte array. For convenience, two seeds are also +// hashed into the result. +uint64_t CityHash64WithSeeds(const char *s, size_t len, uint64_t seed0, + uint64_t seed1); + +// Hash function for a byte array. +uint128 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. +uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed); + +// Hash function for a byte array. Most useful in 32-bit binaries. +uint32_t CityHash32(const char *s, size_t len); + +// Hash 128 input bits down to 64 bits of output. +// This is intended to be a reasonably good hash function. +inline uint64_t Hash128to64(const uint128 &x) { + // Murmur-inspired hashing. + const uint64_t kMul = 0x9ddfea08eb382d69ULL; + uint64_t a = (Uint128Low64(x) ^ Uint128High64(x)) * kMul; + a ^= (a >> 47); + uint64_t b = (Uint128High64(x) ^ a) * kMul; + b ^= (b >> 47); + b *= kMul; + return b; +} + +} // namespace hash_internal +} // namespace absl + +#endif // ABSL_HASH_INTERNAL_CITY_H_ -- cgit v1.2.3