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73 行
1.9 KiB
73 行
1.9 KiB
// 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 <algorithm>
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#include <stdint.h>
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#include "leveldb/comparator.h"
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#include "leveldb/slice.h"
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#include "util/logging.h"
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namespace leveldb {
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Comparator::~Comparator() { }
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namespace {
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class BytewiseComparatorImpl : public Comparator {
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public:
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BytewiseComparatorImpl() { }
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virtual const char* Name() const {
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return "leveldb.BytewiseComparator";
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}
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virtual int Compare(const Slice& a, const Slice& b) const {
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return a.compare(b);
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}
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virtual void FindShortestSeparator(
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std::string* start,
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const Slice& limit) const {
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// Find length of common prefix
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size_t min_length = std::min(start->size(), limit.size());
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size_t diff_index = 0;
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while ((diff_index < min_length) &&
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((*start)[diff_index] == limit[diff_index])) {
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diff_index++;
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}
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if (diff_index >= min_length) {
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// Do not shorten if one string is a prefix of the other
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} else {
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uint8_t diff_byte = static_cast<uint8_t>((*start)[diff_index]);
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if (diff_byte < static_cast<uint8_t>(0xff) &&
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diff_byte + 1 < static_cast<uint8_t>(limit[diff_index])) {
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(*start)[diff_index]++;
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start->resize(diff_index + 1);
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assert(Compare(*start, limit) < 0);
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}
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}
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}
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virtual void FindShortSuccessor(std::string* key) const {
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// Find first character that can be incremented
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size_t n = key->size();
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for (size_t i = 0; i < n; i++) {
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const uint8_t byte = (*key)[i];
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if (byte != static_cast<uint8_t>(0xff)) {
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(*key)[i] = byte + 1;
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key->resize(i+1);
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return;
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}
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}
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// *key is a run of 0xffs. Leave it alone.
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}
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};
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}
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static const BytewiseComparatorImpl bytewise;
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const Comparator* BytewiseComparator() {
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return &bytewise;
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}
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}
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