mirror of
https://github.com/facebook/rocksdb.git
synced 2024-11-26 16:30:56 +00:00
7bee48bdbd
Summary: - Avoid `strdup` to use jemalloc on Windows - Use `size_t` for consistency - Add GCC 8 to Travis - Add CMAKE_BUILD_TYPE=Release to Travis Pull Request resolved: https://github.com/facebook/rocksdb/pull/3433 Differential Revision: D6837948 Pulled By: sagar0 fbshipit-source-id: b8543c3a4da9cd07ee9a33f9f4623188e233261f
58 lines
1.9 KiB
C++
58 lines
1.9 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
|
|
// This source code is licensed under both the GPLv2 (found in the
|
|
// COPYING file in the root directory) and Apache 2.0 License
|
|
// (found in the LICENSE.Apache file in the root directory).
|
|
//
|
|
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style license that can be
|
|
// found in the LICENSE file. See the AUTHORS file for names of contributors.
|
|
|
|
#include <string.h>
|
|
#include "util/coding.h"
|
|
#include "util/hash.h"
|
|
#include "util/util.h"
|
|
|
|
namespace rocksdb {
|
|
|
|
uint32_t Hash(const char* data, size_t n, uint32_t seed) {
|
|
// Similar to murmur hash
|
|
const uint32_t m = 0xc6a4a793;
|
|
const uint32_t r = 24;
|
|
const char* limit = data + n;
|
|
uint32_t h = static_cast<uint32_t>(seed ^ (n * m));
|
|
|
|
// Pick up four bytes at a time
|
|
while (data + 4 <= limit) {
|
|
uint32_t w = DecodeFixed32(data);
|
|
data += 4;
|
|
h += w;
|
|
h *= m;
|
|
h ^= (h >> 16);
|
|
}
|
|
|
|
// Pick up remaining bytes
|
|
switch (limit - data) {
|
|
// Note: The original hash implementation used data[i] << shift, which
|
|
// promotes the char to int and then performs the shift. If the char is
|
|
// negative, the shift is undefined behavior in C++. The hash algorithm is
|
|
// part of the format definition, so we cannot change it; to obtain the same
|
|
// behavior in a legal way we just cast to uint32_t, which will do
|
|
// sign-extension. To guarantee compatibility with architectures where chars
|
|
// are unsigned we first cast the char to int8_t.
|
|
case 3:
|
|
h += static_cast<uint32_t>(static_cast<int8_t>(data[2])) << 16;
|
|
FALLTHROUGH_INTENDED;
|
|
case 2:
|
|
h += static_cast<uint32_t>(static_cast<int8_t>(data[1])) << 8;
|
|
FALLTHROUGH_INTENDED;
|
|
case 1:
|
|
h += static_cast<uint32_t>(static_cast<int8_t>(data[0]));
|
|
h *= m;
|
|
h ^= (h >> r);
|
|
break;
|
|
}
|
|
return h;
|
|
}
|
|
|
|
} // namespace rocksdb
|