City.h

// Copyright (c) 2011 Google, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.
//
// CityHash, by Geoff Pike and Jyrki Alakuijala
//
// This file provides a few functions for hashing strings. On x86-64
// hardware in 2011, CityHash64() is faster than other high-quality
// hash functions, such as Murmur.  This is largely due to higher
// instruction-level parallelism.  CityHash64() and CityHash128() also perform
// well on hash-quality tests.
//
// CityHash128() is optimized for relatively long strings and returns
// a 128-bit hash.  For strings more than about 2000 bytes it can be
// faster than CityHash64().
//
// Functions in the CityHash family are not suitable for cryptography.
//
// WARNING: This code has not been 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.
//
// 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 CITY_HASH_H_
#define CITY_HASH_H_

#include "Platform.h"
#include <stdlib.h> // for size_t.
// #include <stdint.h>
#include <utility>

typedef std::pair<uint64_t, uint64_t> uint128;

inline uint64_t Uint128Low64(const uint128 &x) { return x.first; }
inline uint64_t Uint128High64(const uint128 &x) { return x.second; }

// Hash functions for a byte array.
uint32_t CityHash32WithSeed(const char *buf, size_t len, uint32_t seed);
uint64_t 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.
uint64_t CityHash64WithSeed(const char *buf, 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 *buf, 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 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;
}

// Conditionally include declarations for versions of City that require SSE4.2
// instructions to be available.
#if defined(__SSE4_2__) && defined(__x86_64__)

// Hash function for a byte array.
uint128 CityHashCrc128(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 CityHashCrc128WithSeed(const char *s, size_t len, uint128 seed);

// Hash function for a byte array.  Sets result[0] ... result[3].
void CityHashCrc256(const char *s, size_t len, uint64_t *result);

#endif // __SSE4_2__

#endif // CITY_HASH_H_