be/src/gutil/hash/city.h

// Copyright 2010 Google Inc. All Rights Reserved.
// Authors: gpike@google.com (Geoff Pike), jyrki@google.com (Jyrki Alakuijala)
//
// This file provides a few functions for hashing strings.  On x86-64
// hardware as of early 2010, CityHash64() is much faster than
// MurmurHash64(), and passes the quality-of-hash tests in
// ./hasheval/hasheval_test.cc, among others, with flying colors.  The
// difference in speed can be a factor of two for strings of 50 to 64
// bytes, and sometimes even more for cache-resident longer strings.
//
// 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.
//
// 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 UTIL_HASH_CITY_H_
#define UTIL_HASH_CITY_H_

#include <stddef.h>  // for size_t.

#include "gutil/int128.h"
#include "gutil/integral_types.h"

namespace util_hash {

// Hash function for a byte array.
// The mapping may change from time to time.
uint64 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.  The mapping may change from time to time.
uint64 CityHash64WithSeed(const char *buf, size_t len, uint64 seed);

// Hash function for a byte array.  For convenience, two seeds are also
// hashed into the result.  The mapping may change from time to time.
uint64 CityHash64WithSeeds(const char *buf, size_t len,
                           uint64 seed0, uint64 seed1);

// Hash function for a byte array.  The mapping will never change.
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.  The mapping will never change.
uint128 CityHash128WithSeed(const char *s, size_t len, uint128 seed);

}  // namespace util_hash

#endif  // UTIL_HASH_CITY_H_