rocksdb/util/comparator.cc

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
2017-04-28 02:50:56 +02:00
// 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 <algorithm>
#include <memory>
#include <stdint.h>
#include "rocksdb/comparator.h"
#include "rocksdb/slice.h"
#include "port/port.h"
#include "util/logging.h"
namespace rocksdb {
Comparator::~Comparator() { }
namespace {
class BytewiseComparatorImpl : public Comparator {
public:
BytewiseComparatorImpl() { }
virtual const char* Name() const override {
return "leveldb.BytewiseComparator";
}
virtual int Compare(const Slice& a, const Slice& b) const override {
return a.compare(b);
}
virtual bool Equal(const Slice& a, const Slice& b) const override {
return a == b;
}
virtual void FindShortestSeparator(std::string* start,
const Slice& limit) const override {
// Find length of common prefix
size_t min_length = std::min(start->size(), limit.size());
size_t diff_index = 0;
while ((diff_index < min_length) &&
((*start)[diff_index] == limit[diff_index])) {
diff_index++;
}
if (diff_index >= min_length) {
// Do not shorten if one string is a prefix of the other
} else {
uint8_t start_byte = static_cast<uint8_t>((*start)[diff_index]);
uint8_t limit_byte = static_cast<uint8_t>(limit[diff_index]);
if (start_byte >= limit_byte || (diff_index == start->size() - 1)) {
// Cannot shorten since limit is smaller than start or start is
// already the shortest possible.
return;
}
assert(start_byte < limit_byte);
if (diff_index < limit.size() - 1 || start_byte + 1 < limit_byte) {
(*start)[diff_index]++;
start->resize(diff_index + 1);
} else {
// v
// A A 1 A A A
// A A 2
//
// Incrementing the current byte will make start bigger than limit, we
// will skip this byte, and find the first non 0xFF byte in start and
// increment it.
diff_index++;
while (diff_index < start->size()) {
// Keep moving until we find the first non 0xFF byte to
// increment it
if (static_cast<uint8_t>((*start)[diff_index]) <
static_cast<uint8_t>(0xff)) {
(*start)[diff_index]++;
start->resize(diff_index + 1);
break;
}
diff_index++;
}
}
assert(Compare(*start, limit) < 0);
}
}
virtual void FindShortSuccessor(std::string* key) const override {
// Find first character that can be incremented
size_t n = key->size();
for (size_t i = 0; i < n; i++) {
const uint8_t byte = (*key)[i];
if (byte != static_cast<uint8_t>(0xff)) {
(*key)[i] = byte + 1;
key->resize(i+1);
return;
}
}
// *key is a run of 0xffs. Leave it alone.
}
};
class ReverseBytewiseComparatorImpl : public BytewiseComparatorImpl {
public:
ReverseBytewiseComparatorImpl() { }
virtual const char* Name() const override {
return "rocksdb.ReverseBytewiseComparator";
}
virtual int Compare(const Slice& a, const Slice& b) const override {
return -a.compare(b);
}
};
}// namespace
const Comparator* BytewiseComparator() {
static BytewiseComparatorImpl bytewise;
return &bytewise;
}
const Comparator* ReverseBytewiseComparator() {
static ReverseBytewiseComparatorImpl rbytewise;
return &rbytewise;
}
} // namespace rocksdb