ceph/src/rocksdb/util/hash.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5 //
   6 // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
   7 // Use of this source code is governed by a BSD-style license that can be
   8 // found in the LICENSE file. See the AUTHORS file for names of contributors.
   9 //
  10 // Simple hash function used for internal data structures
  11
  12 #pragma once
  13 #include <stddef.h>
  14 #include <stdint.h>
  15
  16 #include "rocksdb/slice.h"
  17 #include "util/murmurhash.h"
  18
  19 namespace rocksdb {
  20
  21 // Non-persistent hash. Only used for in-memory data structure
  22 // The hash results are applicable to change.
  23 extern uint64_t NPHash64(const char* data, size_t n, uint32_t seed);
  24
  25 extern uint32_t Hash(const char* data, size_t n, uint32_t seed);
  26
  27 inline uint32_t BloomHash(const Slice& key) {
  28   return Hash(key.data(), key.size(), 0xbc9f1d34);
  29 }
  30
  31 inline uint64_t GetSliceNPHash64(const Slice& s) {
  32   return NPHash64(s.data(), s.size(), 0);
  33 }
  34
  35 inline uint32_t GetSliceHash(const Slice& s) {
  36   return Hash(s.data(), s.size(), 397);
  37 }
  38
  39 inline uint64_t NPHash64(const char* data, size_t n, uint32_t seed) {
  40   // Right now murmurhash2B is used. It should able to be freely
  41   // changed to a better hash, without worrying about backward
  42   // compatibility issue.
  43   return MURMUR_HASH(data, static_cast<int>(n),
  44                      static_cast<unsigned int>(seed));
  45 }
  46
  47 // std::hash compatible interface.
  48 struct SliceHasher {
  49   uint32_t operator()(const Slice& s) const { return GetSliceHash(s); }
  50 };
  51
  52 }  // namespace rocksdb