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The shuffling algorithm uses a naïve bloom filter to provide random uniformity, avoiding items that were recently played. With 32 bits, double hashing, and an error rate of ~10%, this bloom filter should be able to hold around ~16 keys, which should be sufficient to give the illusion of fairness to the shuffling algorithm. This avoids having to shuffle the playlist itself (user might have spent quite a bit of time to sort them, so it's not a good idea to mess with it), or having to create a proxy model that shuffles (that could potentially use quite a bit of memory).
71 lines
1.9 KiB
C++
71 lines
1.9 KiB
C++
/*
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* Copyright (c) 2021, the SerenityOS developers.
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* Copyright (c) 2021, Leandro A. F. Pereira <leandro@tia.mat.br>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include "M3UParser.h"
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#include "PlaylistWidget.h"
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#include <AK/StringHash.h>
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#include <AK/StringView.h>
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#include <AK/Vector.h>
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class Playlist {
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public:
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Playlist()
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: m_model(adopt_ref(*new PlaylistModel()))
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{
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}
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bool load(StringView);
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RefPtr<PlaylistModel> model() { return m_model; }
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int size() { return m_model->items().size(); }
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StringView next();
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StringView previous();
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void set_looping(bool looping) { m_looping = looping; }
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bool looping() const { return m_looping; }
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void set_shuffling(bool shuffling) { m_shuffling = shuffling; }
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bool shuffling() const { return m_shuffling; }
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private:
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// This naïve bloom filter is used in the shuffling algorithm to
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// provide random uniformity, avoiding playing items that were recently
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// played.
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class BloomFilter {
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public:
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void reset() { m_bitmap = 0; }
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void add(const StringView key) { m_bitmap |= mask_for_key(key); }
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bool maybe_contains(const StringView key) const
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{
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auto mask = mask_for_key(key);
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return (m_bitmap & mask) == mask;
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}
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private:
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u64 mask_for_key(StringView key) const
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{
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auto key_chars = key.characters_without_null_termination();
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auto hash1 = string_hash(key_chars, key.length(), 0xdeadbeef);
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auto hash2 = string_hash(key_chars, key.length(), 0xbebacafe);
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return 1ULL << (hash1 & 63) | 1ULL << (hash2 & 63);
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}
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u64 m_bitmap { 0 };
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};
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void try_fill_missing_info(Vector<M3UEntry>&, StringView);
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RefPtr<PlaylistModel> m_model;
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bool m_looping { false };
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bool m_shuffling { false };
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BloomFilter m_previously_played_paths;
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int m_next_index_to_play { 0 };
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};
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