diff --git a/AK/CircularBuffer.cpp b/AK/CircularBuffer.cpp index 7ea131b13d2..dc42c8bd516 100644 --- a/AK/CircularBuffer.cpp +++ b/AK/CircularBuffer.cpp @@ -272,7 +272,7 @@ ErrorOr SearchableCircularBuffer::create_initialized(B return circular_buffer; } -ErrorOr> SearchableCircularBuffer::find_copy_in_seekback(size_t maximum_length, size_t minimum_length, Optional const&> distance_hints) const +ErrorOr> SearchableCircularBuffer::find_copy_in_seekback(size_t maximum_length, size_t minimum_length) const { VERIFY(minimum_length > 0); @@ -285,67 +285,104 @@ ErrorOr> SearchableCircularBuffer::find_ Vector matches; - if (distance_hints.has_value()) { - // If we have any hints, verify and use those. - for (auto const& distance : distance_hints.value()) { - // TODO: This does not yet support looping repetitions. - if (distance < minimum_length) - continue; + // Use memmem to find the initial matches. + // 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. + // 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. + size_t haystack_offset_from_start = 0; + Vector haystack; + haystack.append(next_read_span_with_seekback(m_seekback_limit)); + if (haystack[0].size() < m_seekback_limit - used_space()) + haystack.append(next_read_span_with_seekback(m_seekback_limit - haystack[0].size())); - auto needle_offset = (capacity() + m_reading_head) % capacity(); - auto haystack_offset = (capacity() + m_reading_head - distance) % capacity(); + haystack.last() = haystack.last().trim(haystack.last().size() - used_space()); - for (size_t i = 0; i < minimum_length; i++) { - if (m_buffer[needle_offset] != m_buffer[haystack_offset]) - break; + auto needle = next_read_span().trim(minimum_length); - needle_offset = (needle_offset + 1) % capacity(); - haystack_offset = (haystack_offset + 1) % capacity(); + auto memmem_match = AK::memmem(haystack.begin(), haystack.end(), needle); + while (memmem_match.has_value()) { + auto match_offset = memmem_match.release_value(); - if (i + 1 == minimum_length) - TRY(matches.try_empend(distance, minimum_length)); + // Add the match to the list of matches to work with. + TRY(matches.try_empend(m_seekback_limit - used_space() - haystack_offset_from_start - match_offset, minimum_length)); + + auto size_to_discard = match_offset + 1; + + // Trim away the already processed bytes from the haystack. + haystack_offset_from_start += size_to_discard; + while (size_to_discard > 0) { + if (haystack[0].size() < size_to_discard) { + size_to_discard -= haystack[0].size(); + haystack.remove(0); + } else { + haystack[0] = haystack[0].slice(size_to_discard); + break; } } - } else { - // Otherwise, use memmem to find the initial matches. - // 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. - // 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. - size_t haystack_offset_from_start = 0; - Vector haystack; - haystack.append(next_read_span_with_seekback(m_seekback_limit)); - if (haystack[0].size() < m_seekback_limit - used_space()) - haystack.append(next_read_span_with_seekback(m_seekback_limit - haystack[0].size())); - haystack.last() = haystack.last().trim(haystack.last().size() - used_space()); + if (haystack.size() == 0) + break; - auto needle = next_read_span().trim(minimum_length); + // Try and find the next match. + memmem_match = AK::memmem(haystack.begin(), haystack.end(), needle); + } - auto memmem_match = AK::memmem(haystack.begin(), haystack.end(), needle); - while (memmem_match.has_value()) { - auto match_offset = memmem_match.release_value(); + // 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. + // For the remaining part, we will keep checking the next byte incrementally and keep eliminating matches until we eliminated all of them. + Vector next_matches; - // Add the match to the list of matches to work with. - TRY(matches.try_empend(m_seekback_limit - used_space() - haystack_offset_from_start - match_offset, minimum_length)); + for (size_t offset = minimum_length; offset < maximum_length; offset++) { + auto needle_data = m_buffer[(capacity() + m_reading_head + offset) % capacity()]; - auto size_to_discard = match_offset + 1; + for (auto const& match : matches) { + auto haystack_data = m_buffer[(capacity() + m_reading_head - match.distance + offset) % capacity()]; - // Trim away the already processed bytes from the haystack. - haystack_offset_from_start += size_to_discard; - while (size_to_discard > 0) { - if (haystack[0].size() < size_to_discard) { - size_to_discard -= haystack[0].size(); - haystack.remove(0); - } else { - haystack[0] = haystack[0].slice(size_to_discard); - break; - } - } + if (haystack_data != needle_data) + continue; - if (haystack.size() == 0) + TRY(next_matches.try_empend(match.distance, match.length + 1)); + } + + if (next_matches.size() == 0) + return matches; + + swap(matches, next_matches); + next_matches.clear_with_capacity(); + } + + return matches; +} + +ErrorOr> SearchableCircularBuffer::find_copy_in_seekback(Vector const& distances, size_t maximum_length, size_t minimum_length) const +{ + VERIFY(minimum_length > 0); + + // Clip the maximum length to the amount of data that we actually store. + if (maximum_length > m_used_space) + maximum_length = m_used_space; + + if (maximum_length < minimum_length) + return Vector {}; + + Vector matches; + + // Verify all hints that we have. + for (auto const& distance : distances) { + // TODO: This does not yet support looping repetitions. + if (distance < minimum_length) + continue; + + auto needle_offset = (capacity() + m_reading_head) % capacity(); + auto haystack_offset = (capacity() + m_reading_head - distance) % capacity(); + + for (size_t i = 0; i < minimum_length; i++) { + if (m_buffer[needle_offset] != m_buffer[haystack_offset]) break; - // Try and find the next match. - memmem_match = AK::memmem(haystack.begin(), haystack.end(), needle); + needle_offset = (needle_offset + 1) % capacity(); + haystack_offset = (haystack_offset + 1) % capacity(); + + if (i + 1 == minimum_length) + TRY(matches.try_empend(distance, minimum_length)); } } diff --git a/AK/CircularBuffer.h b/AK/CircularBuffer.h index c58b2497508..11ba360c9c6 100644 --- a/AK/CircularBuffer.h +++ b/AK/CircularBuffer.h @@ -72,7 +72,8 @@ public: /// This searches the seekback buffer (between read head and limit) for occurrences where it matches the next `length` bytes from the read buffer. /// Supplying any hints will only consider those distances, in case existing offsets need to be validated. /// Note that, since we only start searching at the read head, the length between read head and write head is excluded from the distance. - ErrorOr> find_copy_in_seekback(size_t maximum_length, size_t minimum_length = 2, Optional const&> distance_hints = {}) const; + ErrorOr> find_copy_in_seekback(size_t maximum_length, size_t minimum_length = 2) const; + ErrorOr> find_copy_in_seekback(Vector const& distances, size_t maximum_length, size_t minimum_length = 2) const; private: SearchableCircularBuffer(ByteBuffer); diff --git a/Tests/AK/TestCircularBuffer.cpp b/Tests/AK/TestCircularBuffer.cpp index c5a71a49a4f..45d694e863b 100644 --- a/Tests/AK/TestCircularBuffer.cpp +++ b/Tests/AK/TestCircularBuffer.cpp @@ -412,7 +412,7 @@ TEST_CASE(find_copy_in_seekback) { // Find the largest matches with a length between 1 and 2 (selected "AB", everything smaller gets eliminated). - auto matches = MUST(buffer.find_copy_in_seekback(2, 1, Vector { 6ul, 9ul })); + auto matches = MUST(buffer.find_copy_in_seekback(Vector { 6ul, 9ul }, 2, 1)); EXPECT_EQ(matches.size(), 2ul); EXPECT_EQ(matches[0].distance, 6ul); EXPECT_EQ(matches[0].length, 2ul); @@ -422,13 +422,13 @@ TEST_CASE(find_copy_in_seekback) { // Check that we don't find anything for hints before the valid range. - auto matches = MUST(buffer.find_copy_in_seekback(2, 1, Vector { 0ul })); + auto matches = MUST(buffer.find_copy_in_seekback(Vector { 0ul }, 2, 1)); EXPECT_EQ(matches.size(), 0ul); } { // Check that we don't find anything for hints after the valid range. - auto matches = MUST(buffer.find_copy_in_seekback(2, 1, Vector { 12ul })); + auto matches = MUST(buffer.find_copy_in_seekback(Vector { 12ul }, 2, 1)); EXPECT_EQ(matches.size(), 0ul); } diff --git a/Userland/Libraries/LibCompress/Lzma.cpp b/Userland/Libraries/LibCompress/Lzma.cpp index 59e4ce47bd8..6dfef752804 100644 --- a/Userland/Libraries/LibCompress/Lzma.cpp +++ b/Userland/Libraries/LibCompress/Lzma.cpp @@ -992,13 +992,13 @@ ErrorOr LzmaCompressor::encode_match_type(MatchType match_type) ErrorOr LzmaCompressor::encode_once() { // Check if any of our existing match distances are currently usable. - Vector const existing_distance_hints { + Vector const existing_distances { m_rep0 + normalized_to_real_match_distance_offset, m_rep1 + normalized_to_real_match_distance_offset, m_rep2 + normalized_to_real_match_distance_offset, m_rep3 + normalized_to_real_match_distance_offset, }; - auto existing_distance_results = TRY(m_dictionary->find_copy_in_seekback(m_dictionary->used_space(), normalized_to_real_match_length_offset, existing_distance_hints)); + auto existing_distance_results = TRY(m_dictionary->find_copy_in_seekback(existing_distances, m_dictionary->used_space(), normalized_to_real_match_length_offset)); if (existing_distance_results.size() > 0) { auto selected_match = existing_distance_results[0];