906f3dca72
Summary: this is the key component extracted from diff: https://reviews.facebook.net/D14271 I separate it to a dedicated patch to make the review easier. Test Plan: added a unit test and passed it. Reviewers: haobo, sdong, dhruba CC: leveldb Differential Revision: https://reviews.facebook.net/D16245
50 lines
1.2 KiB
C++
50 lines
1.2 KiB
C++
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#include <string.h>
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#include "util/coding.h"
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#include "util/hash.h"
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namespace rocksdb {
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uint32_t Hash(const char* data, size_t n, uint32_t seed) {
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// Similar to murmur hash
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const uint32_t m = 0xc6a4a793;
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const uint32_t r = 24;
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const char* limit = data + n;
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uint32_t h = seed ^ (n * m);
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// Pick up four bytes at a time
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while (data + 4 <= limit) {
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uint32_t w = DecodeFixed32(data);
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data += 4;
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h += w;
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h *= m;
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h ^= (h >> 16);
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}
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// Pick up remaining bytes
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switch (limit - data) {
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case 3:
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h += data[2] << 16;
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// fall through
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case 2:
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h += data[1] << 8;
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// fall through
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case 1:
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h += data[0];
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h *= m;
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h ^= (h >> r);
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break;
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}
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return h;
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}
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} // namespace rocksdb
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