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https://github.com/LadybirdBrowser/ladybird
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f175a00003
These new traits are identical to `Traits<Integral>`, except that calling `.hash()` will return the value itself instead of hashing it. This should be used in cases where either the value is already a proper hash, or using the value as a hash will yield "good enough" performance in e.g. HashTable. Types larger than 32 bits are folded in on themselves. Collision tests on some popular hashing algorithms show that XOR folding slightly increases the number of collisions, but this allows `IdentityHashTraits` not to make any assumptions on which bits are the most relevant for the final hash.
106 lines
3.9 KiB
C++
106 lines
3.9 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/Forward.h>
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#include <AK/HashMap.h>
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#include <AK/Noncopyable.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, IdentityHashTraits<unsigned>> 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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