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AK+LibCompress: Remove the Deflate back-reference intermediate buffer

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Instead of reading bytes from the output stream into a buffer, just to
immediately write them back out, we can skip the middle-man and copy the
bytes directly into the output buffer.
This commit is contained in:
Timothy Flynn 2023-03-30 14:02:22 -04:00 committed by Andreas Kling
parent 9f238793e0
commit 8b56d82865
Notes: sideshowbarker 2024-07-16 23:57:20 +09:00 
Author: https://github.com/trflynn89
Commit: https://github.com/SerenityOS/serenity/commit/8b56d82865
Pull-request: https://github.com/SerenityOS/serenity/pull/18106
3 changed files with 19 additions and 3 deletions
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16
AK/CircularBuffer.cpp
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@ -206,4 +206,20 @@ ErrorOr<size_t> CircularBuffer::fill_from_stream(Stream& stream)
return bytes.size();
}
ErrorOr<void> CircularBuffer::copy_from_seekback(size_t distance, size_t length)
{
if (distance > m_seekback_limit)
return Error::from_string_literal("Tried a seekback copy beyond the seekback limit");
while (length > 0) {
auto next_span = next_read_span_with_seekback(distance);
if (next_span.size() == 0)
break;
length -= write(next_span.trim(length));
}
return {};
}
}

2
AK/CircularBuffer.h
View file

@ -33,6 +33,8 @@ public:
/// before the current write pointer and allows for reading already-read data.
ErrorOr<Bytes> read_with_seekback(Bytes bytes, size_t distance);
ErrorOr<void> copy_from_seekback(size_t distance, size_t length);
[[nodiscard]] size_t empty_space() const;
[[nodiscard]] size_t used_space() const;
[[nodiscard]] size_t capacity() const;

4
Userland/Libraries/LibCompress/Deflate.cpp
View file

@ -207,9 +207,7 @@ ErrorOr<bool> DeflateDecompressor::CompressedBlock::try_read_more()
m_decompressor.m_output_buffer.write({ &byte, sizeof(byte) });
}
} else {
Array<u8, DeflateDecompressor::max_back_reference_length> buffer;
auto bytes = TRY(m_decompressor.m_output_buffer.read_with_seekback({ buffer.data(), length }, distance));
m_decompressor.m_output_buffer.write(bytes);
TRY(m_decompressor.m_output_buffer.copy_from_seekback(distance, length));
}
return true;