mirror of
https://github.com/SerenityOS/serenity
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106 lines
3.8 KiB
C++
106 lines
3.8 KiB
C++
/*
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* Copyright (c) 2022, Lucas Chollet <lucas.chollet@free.fr>
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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 <AK/ByteBuffer.h>
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#include <AK/Error.h>
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#include <AK/HashMap.h>
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#include <AK/Noncopyable.h>
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#include <AK/Vector.h>
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namespace AK {
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class CircularBuffer {
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AK_MAKE_NONCOPYABLE(CircularBuffer);
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AK_MAKE_DEFAULT_MOVABLE(CircularBuffer);
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public:
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static ErrorOr<CircularBuffer> create_empty(size_t size);
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static ErrorOr<CircularBuffer> create_initialized(ByteBuffer);
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~CircularBuffer() = default;
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size_t write(ReadonlyBytes bytes);
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Bytes read(Bytes bytes);
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ErrorOr<void> discard(size_t discarded_bytes);
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ErrorOr<size_t> fill_from_stream(Stream&);
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ErrorOr<size_t> flush_to_stream(Stream&);
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/// Compared to `read()`, this starts reading from an offset that is `distance` bytes
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/// before the current write pointer and allows for reading already-read data.
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ErrorOr<Bytes> read_with_seekback(Bytes bytes, size_t distance) const;
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ErrorOr<size_t> copy_from_seekback(size_t distance, size_t length);
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[[nodiscard]] size_t empty_space() const;
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[[nodiscard]] size_t used_space() const;
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[[nodiscard]] size_t capacity() const;
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[[nodiscard]] size_t seekback_limit() const;
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Optional<size_t> offset_of(StringView needle, Optional<size_t> from = {}, Optional<size_t> until = {}) const;
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void clear();
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protected:
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CircularBuffer(ByteBuffer);
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[[nodiscard]] bool is_wrapping_around() const;
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[[nodiscard]] Bytes next_write_span();
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[[nodiscard]] ReadonlyBytes next_read_span(size_t offset = 0) const;
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[[nodiscard]] ReadonlyBytes next_seekback_span(size_t distance) const;
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ByteBuffer m_buffer {};
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size_t m_reading_head {};
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size_t m_used_space {};
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size_t m_seekback_limit {};
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};
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class SearchableCircularBuffer : public CircularBuffer {
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public:
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static ErrorOr<SearchableCircularBuffer> create_empty(size_t size);
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static ErrorOr<SearchableCircularBuffer> create_initialized(ByteBuffer);
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[[nodiscard]] size_t search_limit() const;
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// These functions update the read pointer, so we need to hash any data that we have processed.
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ErrorOr<Bytes> read(Bytes bytes);
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ErrorOr<void> discard(size_t discarded_bytes);
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ErrorOr<size_t> flush_to_stream(Stream& stream);
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struct Match {
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size_t distance;
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size_t length;
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};
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/// This searches the seekback buffer (between read head and limit) for occurrences where it matches the next `length` bytes from the read buffer.
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/// Supplying any hints will only consider those distances, in case existing offsets need to be validated.
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/// Note that, since we only start searching at the read head, the length between read head and write head is excluded from the distance.
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Optional<Match> find_copy_in_seekback(size_t maximum_length, size_t minimum_length = 2);
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Optional<Match> find_copy_in_seekback(ReadonlySpan<size_t> distances, size_t maximum_length, size_t minimum_length = 2) const;
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// The chunk size for which the hash table holds hashes.
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// This is nice for users to know, as picking a minimum match length that is
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// equal or greater than this allows us to completely skip a slow memory search.
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static constexpr size_t HASH_CHUNK_SIZE = 3;
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private:
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// Note: This function has a similar purpose as next_seekback_span, but they differ in their reference point.
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// Seekback operations start counting their distance at the write head, while search operations start counting their distance at the read head.
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[[nodiscard]] ReadonlyBytes next_search_span(size_t distance) const;
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SearchableCircularBuffer(ByteBuffer);
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HashMap<unsigned, size_t> m_hash_location_map;
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HashMap<size_t, size_t> m_location_chain_map;
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ErrorOr<void> insert_location_hash(ReadonlyBytes value, size_t raw_offset);
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ErrorOr<void> hash_last_bytes(size_t count);
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};
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}
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