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7c673cae | 1 | // Copyright (c) 2011-present, Facebook, Inc. All rights reserved. |
11fdf7f2 TL |
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). | |
7c673cae FG |
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 | #include <algorithm> | |
11 | #include <memory> | |
12 | #include <stdint.h> | |
13 | #include "rocksdb/comparator.h" | |
14 | #include "rocksdb/slice.h" | |
15 | #include "port/port.h" | |
16 | #include "util/logging.h" | |
17 | ||
18 | namespace rocksdb { | |
19 | ||
7c673cae FG |
20 | namespace { |
21 | class BytewiseComparatorImpl : public Comparator { | |
22 | public: | |
23 | BytewiseComparatorImpl() { } | |
24 | ||
25 | virtual const char* Name() const override { | |
26 | return "leveldb.BytewiseComparator"; | |
27 | } | |
28 | ||
29 | virtual int Compare(const Slice& a, const Slice& b) const override { | |
30 | return a.compare(b); | |
31 | } | |
32 | ||
33 | virtual bool Equal(const Slice& a, const Slice& b) const override { | |
34 | return a == b; | |
35 | } | |
36 | ||
37 | virtual void FindShortestSeparator(std::string* start, | |
38 | const Slice& limit) const override { | |
39 | // Find length of common prefix | |
40 | size_t min_length = std::min(start->size(), limit.size()); | |
41 | size_t diff_index = 0; | |
42 | while ((diff_index < min_length) && | |
43 | ((*start)[diff_index] == limit[diff_index])) { | |
44 | diff_index++; | |
45 | } | |
46 | ||
47 | if (diff_index >= min_length) { | |
48 | // Do not shorten if one string is a prefix of the other | |
49 | } else { | |
50 | uint8_t start_byte = static_cast<uint8_t>((*start)[diff_index]); | |
51 | uint8_t limit_byte = static_cast<uint8_t>(limit[diff_index]); | |
11fdf7f2 | 52 | if (start_byte >= limit_byte) { |
7c673cae FG |
53 | // Cannot shorten since limit is smaller than start or start is |
54 | // already the shortest possible. | |
55 | return; | |
56 | } | |
57 | assert(start_byte < limit_byte); | |
58 | ||
59 | if (diff_index < limit.size() - 1 || start_byte + 1 < limit_byte) { | |
60 | (*start)[diff_index]++; | |
61 | start->resize(diff_index + 1); | |
62 | } else { | |
63 | // v | |
64 | // A A 1 A A A | |
65 | // A A 2 | |
66 | // | |
67 | // Incrementing the current byte will make start bigger than limit, we | |
68 | // will skip this byte, and find the first non 0xFF byte in start and | |
69 | // increment it. | |
70 | diff_index++; | |
71 | ||
72 | while (diff_index < start->size()) { | |
73 | // Keep moving until we find the first non 0xFF byte to | |
74 | // increment it | |
75 | if (static_cast<uint8_t>((*start)[diff_index]) < | |
76 | static_cast<uint8_t>(0xff)) { | |
77 | (*start)[diff_index]++; | |
78 | start->resize(diff_index + 1); | |
79 | break; | |
80 | } | |
81 | diff_index++; | |
82 | } | |
83 | } | |
84 | assert(Compare(*start, limit) < 0); | |
85 | } | |
86 | } | |
87 | ||
88 | virtual void FindShortSuccessor(std::string* key) const override { | |
89 | // Find first character that can be incremented | |
90 | size_t n = key->size(); | |
91 | for (size_t i = 0; i < n; i++) { | |
92 | const uint8_t byte = (*key)[i]; | |
93 | if (byte != static_cast<uint8_t>(0xff)) { | |
94 | (*key)[i] = byte + 1; | |
95 | key->resize(i+1); | |
96 | return; | |
97 | } | |
98 | } | |
99 | // *key is a run of 0xffs. Leave it alone. | |
100 | } | |
11fdf7f2 TL |
101 | |
102 | virtual bool IsSameLengthImmediateSuccessor(const Slice& s, | |
103 | const Slice& t) const override { | |
104 | if (s.size() != t.size() || s.size() == 0) { | |
105 | return false; | |
106 | } | |
107 | size_t diff_ind = s.difference_offset(t); | |
108 | // same slice | |
109 | if (diff_ind >= s.size()) return false; | |
110 | uint8_t byte_s = static_cast<uint8_t>(s[diff_ind]); | |
111 | uint8_t byte_t = static_cast<uint8_t>(t[diff_ind]); | |
112 | // first different byte must be consecutive, and remaining bytes must be | |
113 | // 0xff for s and 0x00 for t | |
114 | if (byte_s != uint8_t{0xff} && byte_s + 1 == byte_t) { | |
115 | for (size_t i = diff_ind + 1; i < s.size(); ++i) { | |
116 | byte_s = static_cast<uint8_t>(s[i]); | |
117 | byte_t = static_cast<uint8_t>(t[i]); | |
118 | if (byte_s != uint8_t{0xff} || byte_t != uint8_t{0x00}) { | |
119 | return false; | |
120 | } | |
121 | } | |
122 | return true; | |
123 | } else { | |
124 | return false; | |
125 | } | |
126 | } | |
127 | ||
128 | virtual bool CanKeysWithDifferentByteContentsBeEqual() const override { | |
129 | return false; | |
130 | } | |
7c673cae FG |
131 | }; |
132 | ||
133 | class ReverseBytewiseComparatorImpl : public BytewiseComparatorImpl { | |
134 | public: | |
135 | ReverseBytewiseComparatorImpl() { } | |
136 | ||
137 | virtual const char* Name() const override { | |
138 | return "rocksdb.ReverseBytewiseComparator"; | |
139 | } | |
140 | ||
141 | virtual int Compare(const Slice& a, const Slice& b) const override { | |
142 | return -a.compare(b); | |
143 | } | |
7c673cae | 144 | |
11fdf7f2 TL |
145 | void FindShortestSeparator(std::string* start, |
146 | const Slice& limit) const override { | |
147 | // Find length of common prefix | |
148 | size_t min_length = std::min(start->size(), limit.size()); | |
149 | size_t diff_index = 0; | |
150 | while ((diff_index < min_length) && | |
151 | ((*start)[diff_index] == limit[diff_index])) { | |
152 | diff_index++; | |
153 | } | |
154 | ||
155 | assert(diff_index <= min_length); | |
156 | if (diff_index == min_length) { | |
157 | // Do not shorten if one string is a prefix of the other | |
158 | // | |
159 | // We could handle cases like: | |
160 | // V | |
161 | // A A 2 X Y | |
162 | // A A 2 | |
163 | // in a similar way as BytewiseComparator::FindShortestSeparator(). | |
164 | // We keep it simple by not implementing it. We can come back to it | |
165 | // later when needed. | |
166 | } else { | |
167 | uint8_t start_byte = static_cast<uint8_t>((*start)[diff_index]); | |
168 | uint8_t limit_byte = static_cast<uint8_t>(limit[diff_index]); | |
169 | if (start_byte > limit_byte && diff_index < start->size() - 1) { | |
170 | // Case like | |
171 | // V | |
172 | // A A 3 A A | |
173 | // A A 1 B B | |
174 | // | |
175 | // or | |
176 | // v | |
177 | // A A 2 A A | |
178 | // A A 1 B B | |
179 | // In this case "AA2" will be good. | |
180 | #ifndef NDEBUG | |
181 | std::string old_start = *start; | |
182 | #endif | |
183 | start->resize(diff_index + 1); | |
184 | #ifndef NDEBUG | |
185 | assert(old_start >= *start); | |
186 | #endif | |
187 | assert(Slice(*start).compare(limit) > 0); | |
188 | } | |
189 | } | |
190 | } | |
191 | ||
192 | void FindShortSuccessor(std::string* /*key*/) const override { | |
193 | // Don't do anything for simplicity. | |
194 | } | |
195 | ||
196 | virtual bool CanKeysWithDifferentByteContentsBeEqual() const override { | |
197 | return false; | |
198 | } | |
199 | }; | |
7c673cae FG |
200 | }// namespace |
201 | ||
202 | const Comparator* BytewiseComparator() { | |
203 | static BytewiseComparatorImpl bytewise; | |
204 | return &bytewise; | |
205 | } | |
206 | ||
207 | const Comparator* ReverseBytewiseComparator() { | |
208 | static ReverseBytewiseComparatorImpl rbytewise; | |
209 | return &rbytewise; | |
210 | } | |
211 | ||
212 | } // namespace rocksdb |