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SoundPlayer: Implement playlist shuffle mode

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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).
This commit is contained in:
Leandro Pereira 2021-09-30 07:41:00 -07:00 • committed by Andreas Kling
parent 0812965f50
commit 314b8a374b
7 changed files with 106 additions and 11 deletions
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31
Userland/Applications/SoundPlayer/Playlist.h
View file

@ -1,5 +1,6 @@
/*
* Copyright (c) 2021, the SerenityOS developers.
* Copyright (c) 2021, Leandro A. F. Pereira <leandro@tia.mat.br>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -8,6 +9,7 @@
#include "M3UParser.h"
#include "PlaylistWidget.h"
#include <AK/StringHash.h>
#include <AK/StringView.h>
#include <AK/Vector.h>
@ -29,11 +31,40 @@ public:
void set_looping(bool looping) { m_looping = looping; }
bool looping() const { return m_looping; }
void set_shuffling(bool shuffling) { m_shuffling = shuffling; }
bool shuffling() const { return m_shuffling; }
private:
// This naïve bloom filter is used in the shuffling algorithm to
// provide random uniformity, avoiding playing items that were recently
// played.
class BloomFilter {
public:
void reset() { m_bitmap = 0; }
void add(const StringView key) { m_bitmap |= mask_for_key(key); }
bool maybe_contains(const StringView key) const
{
auto mask = mask_for_key(key);
return (m_bitmap & mask) == mask;
}
private:
u64 mask_for_key(StringView key) const
{
auto key_chars = key.characters_without_null_termination();
auto hash1 = string_hash(key_chars, key.length(), 0xdeadbeef);
auto hash2 = string_hash(key_chars, key.length(), 0xbebacafe);
return 1ULL << (hash1 & 63) | 1ULL << (hash2 & 63);
}
u64 m_bitmap { 0 };
};
void try_fill_missing_info(Vector<M3UEntry>&, StringView);
RefPtr<PlaylistModel> m_model;
bool m_looping { false };
bool m_shuffling { false };
BloomFilter m_previously_played_paths;
int m_next_index_to_play { 0 };
};