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https://github.com/SerenityOS/serenity
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046a9faeb3
The "operation modes" of this function have very different focuses, and trying to combine both in a way where we share the most amount of code probably results in the worst performance. Instead, split up the function into "existing distances" and "no existing distances" so that we can optimize either case separately.
416 lines
13 KiB
C++
416 lines
13 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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#include <AK/CircularBuffer.h>
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#include <AK/MemMem.h>
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#include <AK/Stream.h>
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namespace AK {
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CircularBuffer::CircularBuffer(ByteBuffer buffer)
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: m_buffer(move(buffer))
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{
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}
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ErrorOr<CircularBuffer> CircularBuffer::create_empty(size_t size)
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{
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auto temporary_buffer = TRY(ByteBuffer::create_uninitialized(size));
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CircularBuffer circular_buffer { move(temporary_buffer) };
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return circular_buffer;
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}
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ErrorOr<CircularBuffer> CircularBuffer::create_initialized(ByteBuffer buffer)
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{
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CircularBuffer circular_buffer { move(buffer) };
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circular_buffer.m_used_space = circular_buffer.m_buffer.size();
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return circular_buffer;
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}
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size_t CircularBuffer::empty_space() const
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{
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return capacity() - m_used_space;
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}
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size_t CircularBuffer::used_space() const
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{
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return m_used_space;
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}
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size_t CircularBuffer::capacity() const
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{
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return m_buffer.size();
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}
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size_t CircularBuffer::seekback_limit() const
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{
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return m_seekback_limit;
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}
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bool CircularBuffer::is_wrapping_around() const
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{
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return capacity() <= m_reading_head + m_used_space;
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}
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Optional<size_t> CircularBuffer::offset_of(StringView needle, Optional<size_t> from, Optional<size_t> until) const
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{
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auto const read_from = from.value_or(0);
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auto const read_until = until.value_or(m_used_space);
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VERIFY(read_from <= read_until);
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Array<ReadonlyBytes, 2> spans {};
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spans[0] = next_read_span();
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auto const original_span_0_size = spans[0].size();
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if (read_from > 0)
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spans[0] = spans[0].slice(min(spans[0].size(), read_from));
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if (spans[0].size() + read_from > read_until)
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spans[0] = spans[0].trim(read_until - read_from);
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else if (is_wrapping_around())
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spans[1] = m_buffer.span().slice(max(original_span_0_size, read_from) - original_span_0_size, min(read_until, m_used_space) - original_span_0_size);
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auto maybe_found = AK::memmem(spans.begin(), spans.end(), needle.bytes());
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if (maybe_found.has_value())
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*maybe_found += read_from;
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return maybe_found;
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}
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void CircularBuffer::clear()
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{
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m_reading_head = 0;
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m_used_space = 0;
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m_seekback_limit = 0;
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}
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Bytes CircularBuffer::next_write_span()
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{
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if (is_wrapping_around())
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return m_buffer.span().slice(m_reading_head + m_used_space - capacity(), capacity() - m_used_space);
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return m_buffer.span().slice(m_reading_head + m_used_space, capacity() - (m_reading_head + m_used_space));
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}
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ReadonlyBytes CircularBuffer::next_read_span() const
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{
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return m_buffer.span().slice(m_reading_head, min(capacity() - m_reading_head, m_used_space));
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}
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ReadonlyBytes CircularBuffer::next_read_span_with_seekback(size_t distance) const
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{
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VERIFY(m_seekback_limit <= capacity());
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VERIFY(distance <= m_seekback_limit);
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// Note: We are adding the capacity once here to ensure that we can wrap around the negative space by using modulo.
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auto read_offset = (capacity() + m_reading_head + m_used_space - distance) % capacity();
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return m_buffer.span().slice(read_offset, min(capacity() - read_offset, distance));
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}
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size_t CircularBuffer::write(ReadonlyBytes bytes)
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{
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auto remaining = bytes.size();
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while (remaining > 0) {
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auto const next_span = next_write_span();
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if (next_span.size() == 0)
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break;
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auto const written_bytes = bytes.slice(bytes.size() - remaining).copy_trimmed_to(next_span);
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m_used_space += written_bytes;
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m_seekback_limit += written_bytes;
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if (m_seekback_limit > capacity())
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m_seekback_limit = capacity();
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remaining -= written_bytes;
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}
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return bytes.size() - remaining;
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}
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Bytes CircularBuffer::read(Bytes bytes)
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{
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auto remaining = bytes.size();
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while (remaining > 0) {
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auto const next_span = next_read_span();
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if (next_span.size() == 0)
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break;
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auto written_bytes = next_span.copy_trimmed_to(bytes.slice(bytes.size() - remaining));
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m_used_space -= written_bytes;
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m_reading_head += written_bytes;
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if (m_reading_head >= capacity())
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m_reading_head -= capacity();
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remaining -= written_bytes;
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}
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return bytes.trim(bytes.size() - remaining);
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}
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ErrorOr<Bytes> CircularBuffer::read_with_seekback(Bytes bytes, size_t distance)
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{
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if (distance > m_seekback_limit)
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return Error::from_string_literal("Tried a seekback read beyond the seekback limit");
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auto remaining = bytes.size();
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while (remaining > 0) {
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auto const next_span = next_read_span_with_seekback(distance);
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if (next_span.size() == 0)
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break;
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auto written_bytes = next_span.copy_trimmed_to(bytes.slice(bytes.size() - remaining));
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distance -= written_bytes;
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remaining -= written_bytes;
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}
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return bytes.trim(bytes.size() - remaining);
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}
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ErrorOr<void> CircularBuffer::discard(size_t discarding_size)
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{
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if (m_used_space < discarding_size)
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return Error::from_string_literal("Can not discard more data than what the buffer contains");
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m_used_space -= discarding_size;
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m_reading_head = (m_reading_head + discarding_size) % capacity();
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return {};
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}
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ErrorOr<size_t> CircularBuffer::fill_from_stream(Stream& stream)
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{
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auto next_span = next_write_span();
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if (next_span.size() == 0)
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return 0;
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auto bytes = TRY(stream.read_some(next_span));
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m_used_space += bytes.size();
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m_seekback_limit += bytes.size();
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if (m_seekback_limit > capacity())
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m_seekback_limit = capacity();
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return bytes.size();
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}
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ErrorOr<size_t> CircularBuffer::flush_to_stream(Stream& stream)
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{
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auto next_span = next_read_span();
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if (next_span.size() == 0)
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return 0;
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auto written_bytes = TRY(stream.write_some(next_span));
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m_used_space -= written_bytes;
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m_reading_head += written_bytes;
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if (m_reading_head >= capacity())
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m_reading_head -= capacity();
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return written_bytes;
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}
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ErrorOr<size_t> CircularBuffer::copy_from_seekback(size_t distance, size_t length)
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{
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if (distance > m_seekback_limit)
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return Error::from_string_literal("Tried a seekback copy beyond the seekback limit");
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auto remaining_length = length;
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while (remaining_length > 0) {
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if (empty_space() == 0)
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break;
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auto next_span = next_read_span_with_seekback(distance);
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if (next_span.size() == 0)
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break;
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auto length_written = write(next_span.trim(remaining_length));
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remaining_length -= length_written;
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// If we copied right from the end of the seekback area (i.e. our length is larger than the distance)
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// and the last copy was one complete "chunk", we can now double the distance to copy twice as much data in one go.
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if (remaining_length > distance && length_written == distance)
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distance *= 2;
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}
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return length - remaining_length;
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}
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SearchableCircularBuffer::SearchableCircularBuffer(ByteBuffer buffer)
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: CircularBuffer(move(buffer))
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{
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}
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ErrorOr<SearchableCircularBuffer> SearchableCircularBuffer::create_empty(size_t size)
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{
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auto temporary_buffer = TRY(ByteBuffer::create_uninitialized(size));
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SearchableCircularBuffer circular_buffer { move(temporary_buffer) };
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return circular_buffer;
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}
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ErrorOr<SearchableCircularBuffer> SearchableCircularBuffer::create_initialized(ByteBuffer buffer)
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{
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SearchableCircularBuffer circular_buffer { move(buffer) };
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circular_buffer.m_used_space = circular_buffer.m_buffer.size();
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return circular_buffer;
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}
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ErrorOr<Vector<SearchableCircularBuffer::Match>> SearchableCircularBuffer::find_copy_in_seekback(size_t maximum_length, size_t minimum_length) const
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{
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VERIFY(minimum_length > 0);
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// Clip the maximum length to the amount of data that we actually store.
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if (maximum_length > m_used_space)
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maximum_length = m_used_space;
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if (maximum_length < minimum_length)
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return Vector<Match> {};
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Vector<Match> matches;
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// Use memmem to find the initial matches.
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// Note: We have the read head as our reference point, but `next_read_span_with_seekback` isn't aware of that and continues to use the write head.
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// Therefore, we need to make sure to slice off the extraneous bytes from the end of the span and shift the returned distances by the correct amount.
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size_t haystack_offset_from_start = 0;
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Vector<ReadonlyBytes, 2> haystack;
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haystack.append(next_read_span_with_seekback(m_seekback_limit));
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if (haystack[0].size() < m_seekback_limit - used_space())
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haystack.append(next_read_span_with_seekback(m_seekback_limit - haystack[0].size()));
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haystack.last() = haystack.last().trim(haystack.last().size() - used_space());
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auto needle = next_read_span().trim(minimum_length);
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auto memmem_match = AK::memmem(haystack.begin(), haystack.end(), needle);
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while (memmem_match.has_value()) {
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auto match_offset = memmem_match.release_value();
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// Add the match to the list of matches to work with.
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TRY(matches.try_empend(m_seekback_limit - used_space() - haystack_offset_from_start - match_offset, minimum_length));
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auto size_to_discard = match_offset + 1;
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// Trim away the already processed bytes from the haystack.
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haystack_offset_from_start += size_to_discard;
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while (size_to_discard > 0) {
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if (haystack[0].size() < size_to_discard) {
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size_to_discard -= haystack[0].size();
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haystack.remove(0);
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} else {
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haystack[0] = haystack[0].slice(size_to_discard);
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break;
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}
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}
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if (haystack.size() == 0)
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break;
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// Try and find the next match.
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memmem_match = AK::memmem(haystack.begin(), haystack.end(), needle);
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}
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// From now on, all matches that we have stored have at least a length of `minimum_length` and they all refer to the same value.
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// For the remaining part, we will keep checking the next byte incrementally and keep eliminating matches until we eliminated all of them.
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Vector<Match> next_matches;
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for (size_t offset = minimum_length; offset < maximum_length; offset++) {
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auto needle_data = m_buffer[(capacity() + m_reading_head + offset) % capacity()];
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for (auto const& match : matches) {
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auto haystack_data = m_buffer[(capacity() + m_reading_head - match.distance + offset) % capacity()];
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if (haystack_data != needle_data)
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continue;
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TRY(next_matches.try_empend(match.distance, match.length + 1));
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}
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if (next_matches.size() == 0)
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return matches;
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swap(matches, next_matches);
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next_matches.clear_with_capacity();
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}
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return matches;
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}
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ErrorOr<Vector<SearchableCircularBuffer::Match>> SearchableCircularBuffer::find_copy_in_seekback(Vector<size_t> const& distances, size_t maximum_length, size_t minimum_length) const
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{
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VERIFY(minimum_length > 0);
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// Clip the maximum length to the amount of data that we actually store.
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if (maximum_length > m_used_space)
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maximum_length = m_used_space;
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if (maximum_length < minimum_length)
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return Vector<Match> {};
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Vector<Match> matches;
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// Verify all hints that we have.
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for (auto const& distance : distances) {
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// TODO: This does not yet support looping repetitions.
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if (distance < minimum_length)
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continue;
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auto needle_offset = (capacity() + m_reading_head) % capacity();
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auto haystack_offset = (capacity() + m_reading_head - distance) % capacity();
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for (size_t i = 0; i < minimum_length; i++) {
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if (m_buffer[needle_offset] != m_buffer[haystack_offset])
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break;
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needle_offset = (needle_offset + 1) % capacity();
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haystack_offset = (haystack_offset + 1) % capacity();
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if (i + 1 == minimum_length)
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TRY(matches.try_empend(distance, minimum_length));
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}
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}
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// From now on, all matches that we have stored have at least a length of `minimum_length` and they all refer to the same value.
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// For the remaining part, we will keep checking the next byte incrementally and keep eliminating matches until we eliminated all of them.
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Vector<Match> next_matches;
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for (size_t offset = minimum_length; offset < maximum_length; offset++) {
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auto needle_data = m_buffer[(capacity() + m_reading_head + offset) % capacity()];
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for (auto const& match : matches) {
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auto haystack_data = m_buffer[(capacity() + m_reading_head - match.distance + offset) % capacity()];
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if (haystack_data != needle_data)
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continue;
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TRY(next_matches.try_empend(match.distance, match.length + 1));
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}
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if (next_matches.size() == 0)
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return matches;
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swap(matches, next_matches);
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next_matches.clear_with_capacity();
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}
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return matches;
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}
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}
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