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LibCore: Do short forward seeks by discarding bytes from the buffer

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This saves us an actual seek and rereading already stored buffer data in
cases where the seek is entirely covered by the currently buffered data.
This is especially important since we implement `discard` using `seek`
for seekable streams.
This commit is contained in:
Tim Schumacher 2023-01-16 16:46:18 +01:00 • committed by Jelle Raaijmakers
parent bdf991fe76
commit add2e2c076
2 changed files with 30 additions and 3 deletions
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14
Userland/Libraries/LibCore/Stream.h
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@ -819,6 +819,11 @@ public:
m_buffer.clear();
}
ErrorOr<void> discard_bytes(size_t count)
{
return m_buffer.discard(count);
}
private:
ErrorOr<size_t> populate_read_buffer()
{
@ -875,8 +880,15 @@ public:
virtual void close() override { m_helper.stream().close(); }
virtual ErrorOr<off_t> seek(i64 offset, SeekMode mode) override
{
if (mode == SeekMode::FromCurrentPosition)
if (mode == SeekMode::FromCurrentPosition) {
// If possible, seek using the buffer alone.
if (0 <= offset && static_cast<u64>(offset) <= m_helper.buffered_data_size()) {
MUST(m_helper.discard_bytes(offset));
return TRY(m_helper.stream().tell()) - m_helper.buffered_data_size();
}
offset = offset - m_helper.buffered_data_size();
}
auto result = TRY(m_helper.stream().seek(offset, mode));
m_helper.clear_buffer();