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serenity/Userland/Libraries/LibCompress/Lzma.cpp
Tim Schumacher 7000ccf89f LibCompress: Copy LZMA repetitions from the buffer in sequence 
This improves the decompression time of `clang-15.0.7.src.tar.xz` from
5.2 seconds down to about 2.7 seconds.
2023-04-05 07:30:38 -04:00

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/*
* Copyright (c) 2023, Tim Schumacher <timschumi@gmx.de>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <LibCompress/Lzma.h>
namespace Compress {
u32 LzmaHeader::dictionary_size() const
{
// "If the value of dictionary size in properties is smaller than (1 << 12),
// the LZMA decoder must set the dictionary size variable to (1 << 12)."
constexpr u32 minimum_dictionary_size = (1 << 12);
if (m_dictionary_size < minimum_dictionary_size)
return minimum_dictionary_size;
return m_dictionary_size;
}
Optional<u64> LzmaHeader::uncompressed_size() const
{
// We are making a copy of the packed field here because we would otherwise
// pass an unaligned reference to the constructor of Optional, which is
// undefined behavior.
auto uncompressed_size = m_uncompressed_size;
// "If "Uncompressed size" field contains ones in all 64 bits, it means that
// uncompressed size is unknown and there is the "end marker" in stream,
// that indicates the end of decoding point."
if (uncompressed_size == UINT64_MAX)
return {};
// "In opposite case, if the value from "Uncompressed size" field is not
// equal to ((2^64) - 1), the LZMA stream decoding must be finished after
// specified number of bytes (Uncompressed size) is decoded. And if there
// is the "end marker", the LZMA decoder must read that marker also."
return uncompressed_size;
}
ErrorOr<LzmaModelProperties> LzmaHeader::decode_model_properties(u8 input_bits)
{
// "Decodes the following values from the encoded model properties field:
//
// name Range Description
// lc [0, 8] the number of "literal context" bits
// lp [0, 4] the number of "literal pos" bits
// pb [0, 4] the number of "pos" bits
//
// Encoded using `((pb * 5 + lp) * 9 + lc)`."
if (input_bits >= (9 * 5 * 5))
return Error::from_string_literal("Encoded model properties value is larger than the highest possible value");
u8 literal_context_bits = input_bits % 9;
input_bits /= 9;
VERIFY(literal_context_bits >= 0 && literal_context_bits <= 8);
u8 literal_position_bits = input_bits % 5;
input_bits /= 5;
VERIFY(literal_position_bits >= 0 && literal_position_bits <= 4);
u8 position_bits = input_bits;
VERIFY(position_bits >= 0 && position_bits <= 4);
return LzmaModelProperties {
.literal_context_bits = literal_context_bits,
.literal_position_bits = literal_position_bits,
.position_bits = position_bits,
};
}
ErrorOr<LzmaDecompressorOptions> LzmaHeader::as_decompressor_options() const
{
auto model_properties = TRY(decode_model_properties(m_encoded_model_properties));
return Compress::LzmaDecompressorOptions {
.literal_context_bits = model_properties.literal_context_bits,
.literal_position_bits = model_properties.literal_position_bits,
.position_bits = model_properties.position_bits,
.dictionary_size = dictionary_size(),
.uncompressed_size = uncompressed_size(),
.reject_end_of_stream_marker = false,
};
}
void LzmaDecompressor::initialize_to_default_probability(Span<Probability> span)
{
for (auto& entry : span)
entry = default_probability;
}
ErrorOr<NonnullOwnPtr<LzmaDecompressor>> LzmaDecompressor::create_from_container(MaybeOwned<Stream> stream, Optional<MaybeOwned<CircularBuffer>> dictionary)
{
auto header = TRY(stream->read_value<LzmaHeader>());
return TRY(LzmaDecompressor::create_from_raw_stream(move(stream), TRY(header.as_decompressor_options()), move(dictionary)));
}
ErrorOr<NonnullOwnPtr<LzmaDecompressor>> LzmaDecompressor::create_from_raw_stream(MaybeOwned<Stream> stream, LzmaDecompressorOptions const& options, Optional<MaybeOwned<CircularBuffer>> dictionary)
{
if (!dictionary.has_value()) {
auto new_dictionary = TRY(CircularBuffer::create_empty(options.dictionary_size));
dictionary = TRY(try_make<CircularBuffer>(move(new_dictionary)));
}
VERIFY((*dictionary)->capacity() >= options.dictionary_size);
// "The LZMA Decoder uses (1 << (lc + lp)) tables with CProb values, where each table contains 0x300 CProb values."
auto literal_probabilities = TRY(FixedArray<Probability>::create(literal_probability_table_size * (1 << (options.literal_context_bits + options.literal_position_bits))));
auto decompressor = TRY(adopt_nonnull_own_or_enomem(new (nothrow) LzmaDecompressor(move(stream), options, dictionary.release_value(), move(literal_probabilities))));
TRY(decompressor->initialize_range_decoder());
return decompressor;
}
LzmaDecompressor::LzmaDecompressor(MaybeOwned<Stream> stream, LzmaDecompressorOptions options, MaybeOwned<CircularBuffer> dictionary, FixedArray<Probability> literal_probabilities)
: m_stream(move(stream))
, m_options(move(options))
, m_dictionary(move(dictionary))
, m_literal_probabilities(move(literal_probabilities))
{
initialize_to_default_probability(m_literal_probabilities.span());
for (auto& array : m_length_to_position_states)
initialize_to_default_probability(array);
for (auto& array : m_binary_tree_distance_probabilities)
initialize_to_default_probability(array);
initialize_to_default_probability(m_alignment_bit_probabilities);
initialize_to_default_probability(m_is_match_probabilities);
initialize_to_default_probability(m_is_rep_probabilities);
initialize_to_default_probability(m_is_rep_g0_probabilities);
initialize_to_default_probability(m_is_rep_g1_probabilities);
initialize_to_default_probability(m_is_rep_g2_probabilities);
initialize_to_default_probability(m_is_rep0_long_probabilities);
}
bool LzmaDecompressor::is_range_decoder_in_clean_state() const
{
return m_range_decoder_code == 0;
}
bool LzmaDecompressor::has_reached_expected_data_size() const
{
if (!m_options.uncompressed_size.has_value())
return false;
return m_total_decoded_bytes >= m_options.uncompressed_size.value();
}
ErrorOr<void> LzmaDecompressor::initialize_range_decoder()
{
// "The LZMA Encoder always writes ZERO in initial byte of compressed stream.
// That scheme allows to simplify the code of the Range Encoder in the
// LZMA Encoder. If initial byte is not equal to ZERO, the LZMA Decoder must
// stop decoding and report error."
{
auto byte = TRY(m_stream->read_value<u8>());
if (byte != 0)
return Error::from_string_literal("Initial byte of data stream is not zero");
}
// Read the initial bytes into the range decoder.
m_range_decoder_code = 0;
for (size_t i = 0; i < 4; i++) {
auto byte = TRY(m_stream->read_value<u8>());
m_range_decoder_code = m_range_decoder_code << 8 | byte;
}
m_range_decoder_range = 0xFFFFFFFF;
return {};
}
ErrorOr<void> LzmaDecompressor::append_input_stream(MaybeOwned<Stream> stream, Optional<u64> uncompressed_size)
{
m_stream = move(stream);
TRY(initialize_range_decoder());
if (m_options.uncompressed_size.has_value() != uncompressed_size.has_value())
return Error::from_string_literal("Appending LZMA streams with mismatching uncompressed size status");
if (uncompressed_size.has_value())
*m_options.uncompressed_size += *uncompressed_size;
return {};
}
ErrorOr<void> LzmaDecompressor::normalize_range_decoder()
{
// "The value of the "Range" variable before each bit decoding can not be smaller
// than ((UInt32)1 << 24). The Normalize() function keeps the "Range" value in
// described range."
constexpr u32 minimum_range_value = 1 << 24;
if (m_range_decoder_range >= minimum_range_value)
return {};
m_range_decoder_range <<= 8;
m_range_decoder_code <<= 8;
m_range_decoder_code |= TRY(m_stream->read_value<u8>());
VERIFY(m_range_decoder_range >= minimum_range_value);
return {};
}
ErrorOr<u8> LzmaDecompressor::decode_direct_bit()
{
m_range_decoder_range >>= 1;
m_range_decoder_code -= m_range_decoder_range;
u32 temp = 0 - (m_range_decoder_code >> 31);
m_range_decoder_code += m_range_decoder_range & temp;
if (m_range_decoder_code == m_range_decoder_range)
return Error::from_string_literal("Reached an invalid state while decoding LZMA stream");
TRY(normalize_range_decoder());
return temp + 1;
}
ErrorOr<u8> LzmaDecompressor::decode_bit_with_probability(Probability& probability)
{
// "The LZMA decoder provides the pointer to CProb variable that contains
// information about estimated probability for symbol 0 and the Range Decoder
// updates that CProb variable after decoding."
// The significance of the shift width is not explained and appears to be a magic constant.
constexpr size_t probability_shift_width = 5;
u32 bound = (m_range_decoder_range >> probability_bit_count) * probability;
if (m_range_decoder_code < bound) {
probability += ((1 << probability_bit_count) - probability) >> probability_shift_width;
m_range_decoder_range = bound;
TRY(normalize_range_decoder());
return 0;
} else {
probability -= probability >> probability_shift_width;
m_range_decoder_code -= bound;
m_range_decoder_range -= bound;
TRY(normalize_range_decoder());
return 1;
}
}
ErrorOr<u16> LzmaDecompressor::decode_symbol_using_bit_tree(size_t bit_count, Span<Probability> probability_tree)
{
VERIFY(bit_count <= sizeof(u16) * 8);
VERIFY(probability_tree.size() >= 1ul << bit_count);
// This has been modified from the reference implementation to unlink the result and the tree index,
// which should allow for better readability.
u16 result = 0;
size_t tree_index = 1;
for (size_t i = 0; i < bit_count; i++) {
u16 next_bit = TRY(decode_bit_with_probability(probability_tree[tree_index]));
result = (result << 1) | next_bit;
tree_index = (tree_index << 1) | next_bit;
}
return result;
}
ErrorOr<u16> LzmaDecompressor::decode_symbol_using_reverse_bit_tree(size_t bit_count, Span<Probability> probability_tree)
{
VERIFY(bit_count <= sizeof(u16) * 8);
VERIFY(probability_tree.size() >= 1ul << bit_count);
u16 result = 0;
size_t tree_index = 1;
for (size_t i = 0; i < bit_count; i++) {
u16 next_bit = TRY(decode_bit_with_probability(probability_tree[tree_index]));
result |= next_bit << i;
tree_index = (tree_index << 1) | next_bit;
}
return result;
}
ErrorOr<void> LzmaDecompressor::decode_literal_to_output_buffer()
{
u8 previous_byte = 0;
if (m_dictionary->seekback_limit() > 0) {
auto read_bytes = MUST(m_dictionary->read_with_seekback({ &previous_byte, sizeof(previous_byte) }, 1));
VERIFY(read_bytes.size() == sizeof(previous_byte));
}
// "To select the table for decoding it uses the context that consists of
// (lc) high bits from previous literal and (lp) low bits from value that
// represents current position in outputStream."
u16 literal_state_bits_from_position = m_total_decoded_bytes & ((1 << m_options.literal_position_bits) - 1);
u16 literal_state_bits_from_output = previous_byte >> (8 - m_options.literal_context_bits);
u16 literal_state = literal_state_bits_from_position << m_options.literal_context_bits | literal_state_bits_from_output;
Span<Probability> selected_probability_table = m_literal_probabilities.span().slice(literal_probability_table_size * literal_state, literal_probability_table_size);
// The result is defined as u16 here and initialized to 1, but we will cut off the top bits before queueing them into the output buffer.
// The top bit is only used to track how much we have decoded already, and to select the correct probability table.
u16 result = 1;
// "If (State > 7), the Literal Decoder also uses "matchByte" that represents
// the byte in OutputStream at position the is the DISTANCE bytes before
// current position, where the DISTANCE is the distance in DISTANCE-LENGTH pair
// of latest decoded match."
// Note: The specification says `(State > 7)`, but the reference implementation does `(State >= 7)`, which is a mismatch.
// Testing `(State > 7)` with actual test files yields errors, so the reference implementation appears to be the correct one.
if (m_state >= 7) {
u8 matched_byte = 0;
auto read_bytes = TRY(m_dictionary->read_with_seekback({ &matched_byte, sizeof(matched_byte) }, current_repetition_offset()));
VERIFY(read_bytes.size() == sizeof(matched_byte));
do {
u8 match_bit = (matched_byte >> 7) & 1;
matched_byte <<= 1;
u8 decoded_bit = TRY(decode_bit_with_probability(selected_probability_table[((1 + match_bit) << 8) + result]));
result = result << 1 | decoded_bit;
if (match_bit != decoded_bit)
break;
} while (result < 0x100);
}
while (result < 0x100)
result = (result << 1) | TRY(decode_bit_with_probability(selected_probability_table[result]));
u8 actual_result = result - 0x100;
size_t written_bytes = m_dictionary->write({ &actual_result, sizeof(actual_result) });
VERIFY(written_bytes == sizeof(actual_result));
m_total_decoded_bytes += sizeof(actual_result);
return {};
}
LzmaDecompressor::LzmaLengthDecoderState::LzmaLengthDecoderState()
{
for (auto& array : m_low_length_probabilities)
initialize_to_default_probability(array);
for (auto& array : m_medium_length_probabilities)
initialize_to_default_probability(array);
initialize_to_default_probability(m_high_length_probabilities);
}
ErrorOr<u16> LzmaDecompressor::decode_normalized_match_length(LzmaLengthDecoderState& length_decoder_state)
{
// "LZMA uses "posState" value as context to select the binary tree
// from LowCoder and MidCoder binary tree arrays:"
u16 position_state = m_total_decoded_bytes & ((1 << m_options.position_bits) - 1);
// "The following scheme is used for the match length encoding:
//
// Binary encoding Binary Tree structure Zero-based match length
// sequence (binary + decimal):
//
// 0 xxx LowCoder[posState] xxx
if (TRY(decode_bit_with_probability(length_decoder_state.m_first_choice_probability)) == 0)
return TRY(decode_symbol_using_bit_tree(3, length_decoder_state.m_low_length_probabilities[position_state].span()));
// 1 0 yyy MidCoder[posState] yyy + 8
if (TRY(decode_bit_with_probability(length_decoder_state.m_second_choice_probability)) == 0)
return TRY(decode_symbol_using_bit_tree(3, length_decoder_state.m_medium_length_probabilities[position_state].span())) + 8;
// 1 1 zzzzzzzz HighCoder zzzzzzzz + 16"
return TRY(decode_symbol_using_bit_tree(8, length_decoder_state.m_high_length_probabilities.span())) + 16;
}
ErrorOr<u32> LzmaDecompressor::decode_normalized_match_distance(u16 normalized_match_length)
{
// "LZMA uses normalized match length (zero-based length)
// to calculate the context state "lenState" do decode the distance value."
u16 length_state = min(normalized_match_length, number_of_length_to_position_states - 1);
// "At first stage the distance decoder decodes 6-bit "posSlot" value with bit
// tree decoder from PosSlotDecoder array."
u16 position_slot = TRY(decode_symbol_using_bit_tree(6, m_length_to_position_states[length_state].span()));
// "The encoding scheme for distance value is shown in the following table:
//
// posSlot (decimal) /
// zero-based distance (binary)
// 0 0
// 1 1
// 2 10
// 3 11
//
// 4 10 x
// 5 11 x
// 6 10 xx
// 7 11 xx
// 8 10 xxx
// 9 11 xxx
// 10 10 xxxx
// 11 11 xxxx
// 12 10 xxxxx
// 13 11 xxxxx
//
// 14 10 yy zzzz
// 15 11 yy zzzz
// 16 10 yyy zzzz
// 17 11 yyy zzzz
// ...
// 62 10 yyyyyyyyyyyyyyyyyyyyyyyyyy zzzz
// 63 11 yyyyyyyyyyyyyyyyyyyyyyyyyy zzzz
//
// where
// "x ... x" means the sequence of binary symbols encoded with binary tree and
// "Reverse" scheme. It uses separated binary tree for each posSlot from 4 to 13.
// "y" means direct bit encoded with range coder.
// "zzzz" means the sequence of four binary symbols encoded with binary
// tree with "Reverse" scheme, where one common binary tree "AlignDecoder"
// is used for all posSlot values."
// "If (posSlot < 4), the "dist" value is equal to posSlot value."
if (position_slot < first_position_slot_with_binary_tree_bits)
return position_slot;
// From here on, the first bit of the distance is always set and the second bit is set if the last bit of the position slot is set.
u32 distance_prefix = ((1 << 1) | ((position_slot & 1) << 0));
// "If (posSlot >= 4), the decoder uses "posSlot" value to calculate the value of
// the high bits of "dist" value and the number of the low bits.
// If (4 <= posSlot < kEndPosModelIndex), the decoder uses bit tree decoders.
// (one separated bit tree decoder per one posSlot value) and "Reverse" scheme."
if (position_slot < first_position_slot_with_direct_encoded_bits) {
size_t number_of_bits_to_decode = (position_slot / 2) - 1;
auto& selected_probability_tree = m_binary_tree_distance_probabilities[position_slot - first_position_slot_with_binary_tree_bits];
return (distance_prefix << number_of_bits_to_decode) | TRY(decode_symbol_using_reverse_bit_tree(number_of_bits_to_decode, selected_probability_tree));
}
// " if (posSlot >= kEndPosModelIndex), the middle bits are decoded as direct
// bits from RangeDecoder and the low 4 bits are decoded with a bit tree
// decoder "AlignDecoder" with "Reverse" scheme."
size_t number_of_direct_bits_to_decode = ((position_slot - first_position_slot_with_direct_encoded_bits) / 2) + 2;
for (size_t i = 0; i < number_of_direct_bits_to_decode; i++) {
distance_prefix = (distance_prefix << 1) | TRY(decode_direct_bit());
}
return (distance_prefix << number_of_alignment_bits) | TRY(decode_symbol_using_reverse_bit_tree(number_of_alignment_bits, m_alignment_bit_probabilities));
}
u32 LzmaDecompressor::current_repetition_offset() const
{
// LZMA never needs to read at offset 0 (i.e. the actual read head of the buffer).
// Instead, the values are remapped so that the rep-value n starts reading n + 1 bytes back.
// The special rep-value 0xFFFFFFFF is reserved for marking the end of the stream,
// so this should never overflow.
VERIFY(m_rep0 < NumericLimits<u32>::max());
return m_rep0 + 1;
}
ErrorOr<Bytes> LzmaDecompressor::read_some(Bytes bytes)
{
while (m_dictionary->used_space() < bytes.size() && m_dictionary->empty_space() != 0) {
if (m_found_end_of_stream_marker)
break;
if (has_reached_expected_data_size()) {
// If the decoder is in a clean state, we assume that this is fine.
if (is_range_decoder_in_clean_state())
break;
// Otherwise, we give it one last try to find the end marker in the remaining data.
}
// "The decoder calculates "state2" variable value to select exact variable from
// "IsMatch" and "IsRep0Long" arrays."
u16 position_state = m_total_decoded_bytes & ((1 << m_options.position_bits) - 1);
u16 state2 = (m_state << maximum_number_of_position_bits) + position_state;
auto update_state_after_literal = [&] {
if (m_state < 4)
m_state = 0;
else if (m_state < 10)
m_state -= 3;
else
m_state -= 6;
};
auto update_state_after_match = [&] {
if (m_state < 7)
m_state = 7;
else
m_state = 10;
};
auto update_state_after_rep = [&] {
if (m_state < 7)
m_state = 8;
else
m_state = 11;
};
auto update_state_after_short_rep = [&] {
if (m_state < 7)
m_state = 9;
else
m_state = 11;
};
auto copy_match_to_buffer = [&](u16 real_length) -> ErrorOr<void> {
VERIFY(!m_leftover_match_length.has_value());
if (m_options.uncompressed_size.has_value() && m_options.uncompressed_size.value() < m_total_decoded_bytes + real_length)
return Error::from_string_literal("Tried to copy match beyond expected uncompressed file size");
auto copied_length = TRY(m_dictionary->copy_from_seekback(current_repetition_offset(), real_length));
m_total_decoded_bytes += copied_length;
real_length -= copied_length;
if (real_length > 0)
m_leftover_match_length = real_length;
return {};
};
// If we have a leftover part of a repeating match, we should finish that first.
if (m_leftover_match_length.has_value()) {
TRY(copy_match_to_buffer(m_leftover_match_length.release_value()));
continue;
}
// "The decoder uses the following code flow scheme to select exact
// type of LITERAL or MATCH:
//
// IsMatch[state2] decode
// 0 - the Literal"
if (TRY(decode_bit_with_probability(m_is_match_probabilities[state2])) == 0) {
// If we are already past the expected uncompressed size, we are already in "look for EOS only" mode.
if (has_reached_expected_data_size())
return Error::from_string_literal("Found literal after reaching expected uncompressed size");
// "At first the LZMA decoder must check that it doesn't exceed
// specified uncompressed size."
// This is already checked for at the beginning of the loop.
// "Then it decodes literal value and puts it to sliding window."
TRY(decode_literal_to_output_buffer());
// "Then the decoder must update the "state" value."
update_state_after_literal();
continue;
}
// " 1 - the Match
// IsRep[state] decode
// 0 - Simple Match"
if (TRY(decode_bit_with_probability(m_is_rep_probabilities[m_state])) == 0) {
// "The distance history table is updated with the following scheme:"
m_rep3 = m_rep2;
m_rep2 = m_rep1;
m_rep1 = m_rep0;
// "The zero-based length is decoded with "LenDecoder"."
u16 normalized_length = TRY(decode_normalized_match_length(m_length_decoder));
// "The state is update with UpdateState_Match function."
update_state_after_match();
// "and the new "rep0" value is decoded with DecodeDistance."
m_rep0 = TRY(decode_normalized_match_distance(normalized_length));
// "If the value of "rep0" is equal to 0xFFFFFFFF, it means that we have
// "End of stream" marker, so we can stop decoding and check finishing
// condition in Range Decoder"
if (m_rep0 == 0xFFFFFFFF) {
// If we should reject end-of-stream markers, do so now.
// Note that this is not part of LZMA, as LZMA allows end-of-stream markers in all contexts, so pure LZMA should never set this option.
if (m_options.reject_end_of_stream_marker)
return Error::from_string_literal("An end-of-stream marker was found, but the LZMA stream is configured to reject them");
// The range decoder condition is checked after breaking out of the loop.
m_found_end_of_stream_marker = true;
continue;
}
// If we are looking for EOS, but haven't found it here, the stream is corrupted.
if (has_reached_expected_data_size())
return Error::from_string_literal("First simple match after the expected uncompressed size is not the EOS marker");
// "If uncompressed size is defined, LZMA decoder must check that it doesn't
// exceed that specified uncompressed size."
// This is being checked for in the common "copy to buffer" implementation.
// "Also the decoder must check that "rep0" value is not larger than dictionary size
// and is not larger than the number of already decoded bytes."
if (current_repetition_offset() > m_dictionary->seekback_limit())
return Error::from_string_literal("rep0 value is larger than the possible lookback size");
// "Then the decoder must copy match bytes as described in
// "The match symbols copying" section."
TRY(copy_match_to_buffer(normalized_length + normalized_to_real_match_length_offset));
continue;
}
// If we are looking for EOS, but find another match type, the stream is also corrupted.
if (has_reached_expected_data_size())
return Error::from_string_literal("First match type after the expected uncompressed size is not a simple match");
// " 1 - Rep Match
// IsRepG0[state] decode
// 0 - the distance is rep0"
if (TRY(decode_bit_with_probability(m_is_rep_g0_probabilities[m_state])) == 0) {
// "LZMA doesn't update the distance history."
// " IsRep0Long[state2] decode
// 0 - Short Rep Match"
if (TRY(decode_bit_with_probability(m_is_rep0_long_probabilities[state2])) == 0) {
// "If the subtype is "Short Rep Match", the decoder updates the state, puts
// the one byte from window to current position in window and goes to next
// MATCH/LITERAL symbol."
update_state_after_short_rep();
TRY(copy_match_to_buffer(1));
continue;
}
// " 1 - Rep Match 0"
// Intentional fallthrough, we just need to make sure to not run the detection for other match types and to not switch around the distance history.
} else {
// " 1 -
// IsRepG1[state] decode
// 0 - Rep Match 1"
if (TRY(decode_bit_with_probability(m_is_rep_g1_probabilities[m_state])) == 0) {
u32 distance = m_rep1;
m_rep1 = m_rep0;
m_rep0 = distance;
}
// " 1 -
// IsRepG2[state] decode
// 0 - Rep Match 2"
else if (TRY(decode_bit_with_probability(m_is_rep_g2_probabilities[m_state])) == 0) {
u32 distance = m_rep2;
m_rep2 = m_rep1;
m_rep1 = m_rep0;
m_rep0 = distance;
}
// " 1 - Rep Match 3"
else {
u32 distance = m_rep3;
m_rep3 = m_rep2;
m_rep2 = m_rep1;
m_rep1 = m_rep0;
m_rep0 = distance;
}
}
// "In other cases (Rep Match 0/1/2/3), it decodes the zero-based
// length of match with "RepLenDecoder" decoder."
u16 normalized_length = TRY(decode_normalized_match_length(m_rep_length_decoder));
// "Then it updates the state."
update_state_after_rep();
// "Then the decoder must copy match bytes as described in
// "The Match symbols copying" section."
TRY(copy_match_to_buffer(normalized_length + normalized_to_real_match_length_offset));
}
if (m_found_end_of_stream_marker || has_reached_expected_data_size()) {
if (m_options.uncompressed_size.has_value() && m_total_decoded_bytes < m_options.uncompressed_size.value())
return Error::from_string_literal("Found end-of-stream marker earlier than expected");
if (!is_range_decoder_in_clean_state())
return Error::from_string_literal("LZMA stream ends in an unclean state");
}
return m_dictionary->read(bytes);
}
ErrorOr<size_t> LzmaDecompressor::write_some(ReadonlyBytes)
{
return Error::from_errno(EBADF);
}
bool LzmaDecompressor::is_eof() const
{
if (m_dictionary->used_space() > 0)
return false;
if (has_reached_expected_data_size())
return true;
return m_found_end_of_stream_marker;
}
bool LzmaDecompressor::is_open() const
{
return true;
}
void LzmaDecompressor::close()
{
}
}
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