112 lines
2.3 KiB
C++
112 lines
2.3 KiB
C++
/*
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* Copyright 2003-2022 The Music Player Daemon Project
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* http://www.musicpd.org
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#ifndef MPD_ID_TABLE_HXX
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#define MPD_ID_TABLE_HXX
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#include "util/Compiler.h"
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#include <cassert>
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/**
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* A table that maps id numbers to position numbers.
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*/
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class IdTable {
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const unsigned size;
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/**
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* How many members of "data" are initialized?
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*
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* The initial value is 1 and not 0 because the first element
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* of the array is never used, because 0 is not a valid song
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* id.
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*/
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unsigned initialized = 1;
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unsigned next;
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int *const data;
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public:
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IdTable(unsigned _size) noexcept
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:size(_size), next(1), data(new int[size]) {
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}
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~IdTable() noexcept {
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delete[] data;
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}
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IdTable(const IdTable &) = delete;
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IdTable &operator=(const IdTable &) = delete;
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int IdToPosition(unsigned id) const noexcept {
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return id < initialized
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? data[id]
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: -1;
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}
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unsigned GenerateId() noexcept {
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assert(next > 0);
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assert(next <= initialized);
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while (true) {
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unsigned id = next;
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++next;
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if (next == size)
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next = 1;
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if (id == initialized) {
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/* the caller will initialize
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data[id] */
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++initialized;
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return id;
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}
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assert(id < initialized);
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if (data[id] < 0)
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return id;
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}
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}
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unsigned Insert(unsigned position) noexcept {
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unsigned id = GenerateId();
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assert(id < initialized);
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data[id] = position;
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return id;
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}
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void Move(unsigned id, unsigned position) noexcept {
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assert(id < initialized);
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assert(data[id] >= 0);
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data[id] = position;
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}
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void Erase(unsigned id) noexcept {
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assert(id < initialized);
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assert(data[id] >= 0);
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data[id] = -1;
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}
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};
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#endif
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