farmhash-c.h

// Copyright (c) 2014 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.
//
// FarmHash, by Geoff Pike

//
// http://code.google.com/p/farmhash/
//
// This file provides a few functions for hashing strings and other
// data.  All of them are high-quality functions in the sense that
// they do well on standard tests such as Austin Appleby's SMHasher.
// They're also fast.  FarmHash is the successor to CityHash.
//
// Functions in the FarmHash family are not suitable for cryptography.
//
// 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 FARMHASH_C_H
#define FARMHASH_C_H

#if defined (__cplusplus)
extern "C" {
#endif

#include <stdlib.h>
#include <stdint.h>

struct uint128_c_t {
  uint64_t a;
  uint64_t b;
};

typedef struct uint128_c_t uint128_c_t;


static inline uint64_t uint128_c_t_low64(const uint128_c_t x) { return x.a; }
static inline uint64_t uint128_c_t_high64(const uint128_c_t x) { return x.b; }

static inline uint128_c_t make_uint128_c_t(uint64_t lo, uint64_t hi) { uint128_c_t x = {lo, hi}; return x; }

// BASIC STRING HASHING

// Hash function for a byte array.
// May change from time to time, may differ on different platforms, may differ
// depending on NDEBUG.
size_t farmhash(const char* s, size_t len);

// Hash function for a byte array.  Most useful in 32-bit binaries.
// May change from time to time, may differ on different platforms, may differ
// depending on NDEBUG.
uint32_t farmhash32(const char* s, size_t len);

// Hash function for a byte array.  For convenience, a 32-bit seed is also
// hashed into the result.
// May change from time to time, may differ on different platforms, may differ
// depending on NDEBUG.
uint32_t farmhash32_with_seed(const char* s, size_t len, uint32_t seed);

// Hash 128 input bits down to 64 bits of output.
// Hash function for a byte array.
// May change from time to time, may differ on different platforms, may differ
// depending on NDEBUG.
uint64_t farmhash64(const char* s, size_t len);

// Hash function for a byte array.  For convenience, a 64-bit seed is also
// hashed into the result.
// May change from time to time, may differ on different platforms, may differ
// depending on NDEBUG.
uint64_t farmhash64_with_seed(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.
// May change from time to time, may differ on different platforms, may differ
// depending on NDEBUG.
uint64_t farmhash64_with_seeds(const char* s, size_t len,
                       uint64_t seed0, uint64_t seed1);

// Hash function for a byte array.
// May change from time to time, may differ on different platforms, may differ
// depending on NDEBUG.
uint128_c_t farmhash128(const char* s, size_t len);

// Hash function for a byte array.  For convenience, a 128-bit seed is also
// hashed into the result.
// May change from time to time, may differ on different platforms, may differ
// depending on NDEBUG.
uint128_c_t farmhash128_with_seed(const char* s, size_t len, uint128_c_t seed);

// BASIC NON-STRING HASHING

// This is intended to be a reasonably good hash function.
// May change from time to time, may differ on different platforms, may differ
// depending on NDEBUG.
static inline uint64_t farmhash128_to_64(uint128_c_t x) {
  // Murmur-inspired hashing.
  const uint64_t k_mul = 0x9ddfea08eb382d69ULL;
  uint64_t a = (uint128_c_t_low64(x) ^ uint128_c_t_high64(x)) * k_mul;
  a ^= (a >> 47);
  uint64_t b = (uint128_c_t_high64(x) ^ a) * k_mul;
  b ^= (b >> 47);
  b *= k_mul;
  return b;
}

// FINGERPRINTING (i.e., good, portable, forever-fixed hash functions)

// Fingerprint function for a byte array.  Most useful in 32-bit binaries.
uint32_t farmhash_fingerprint32(const char* s, size_t len);

// Fingerprint function for a byte array.
uint64_t farmhash_fingerprint64(const char* s, size_t len);

// Fingerprint function for a byte array.
uint128_c_t farmhash_fingerprint128(const char* s, size_t len);

// This is intended to be a good fingerprinting primitive.
// See below for more overloads.
static inline uint64_t farmhash_fingerprint_uint128_c_t(uint128_c_t x) {
  // Murmur-inspired hashing.
  const uint64_t k_mul = 0x9ddfea08eb382d69ULL;
  uint64_t a = (uint128_c_t_low64(x) ^ uint128_c_t_high64(x)) * k_mul;
  a ^= (a >> 47);
  uint64_t b = (uint128_c_t_high64(x) ^ a) * k_mul;
  b ^= (b >> 44);
  b *= k_mul;
  b ^= (b >> 41);
  b *= k_mul;
  return b;
}

// This is intended to be a good fingerprinting primitive.
static inline uint64_t farmhash_fingerprint_uint64_t(uint64_t x) {
  // Murmur-inspired hashing.
  const uint64_t k_mul = 0x9ddfea08eb382d69ULL;
  uint64_t b = x * k_mul;
  b ^= (b >> 44);
  b *= k_mul;
  b ^= (b >> 41);
  b *= k_mul;
  return b;
}

#if defined (__cplusplus)
}
#endif

#endif  // FARMHASH_C_H