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LibCompress/LZW: Use a LittleEndianBitStream

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No need to manually implement bit stream logic when we have a helper for
this task.
This commit is contained in:
Lucas CHOLLET 2023-11-04 17:53:54 -04:00 • committed by Tim Schumacher
parent b00476abac
commit 5e2b049de8
Notes: sideshowbarker 2024-07-16 23:38:54 +09:00
2 changed files with 12 additions and 35 deletions
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41
Userland/Libraries/LibCompress/LZWDecoder.h
View file

@ -7,6 +7,7 @@
#pragma once
#include <AK/BitStream.h>
#include <AK/Debug.h>
#include <AK/Format.h>
#include <AK/IntegralMath.h>
@ -19,8 +20,8 @@ private:
static constexpr int max_code_size = 12;
public:
explicit LZWDecoder(Vector<u8> const& lzw_bytes, u8 min_code_size)
: m_lzw_bytes(lzw_bytes)
explicit LZWDecoder(MaybeOwned<LittleEndianInputBitStream> lzw_stream, u8 min_code_size)
: m_bit_stream(move(lzw_stream))
, m_code_size(min_code_size)
, m_original_code_size(min_code_size)
, m_table_capacity(AK::exp2<u32>(min_code_size))
@ -52,46 +53,20 @@ public:
ErrorOr<u16> next_code()
{
size_t current_byte_index = m_current_bit_index / 8;
if (current_byte_index >= m_lzw_bytes.size()) {
return Error::from_string_literal("LZWDecoder tries to read ouf of bounds");
}
// Extract the code bits using a 32-bit mask to cover the possibility that if
// the current code size > 9 bits then the code can span 3 bytes.
u8 current_bit_offset = m_current_bit_index % 8;
u32 mask = (u32)(m_table_capacity - 1) << current_bit_offset;
// Make a padded copy of the final bytes in the data to ensure we don't read past the end.
if (current_byte_index + sizeof(mask) > m_lzw_bytes.size()) {
u8 padded_last_bytes[sizeof(mask)] = { 0 };
for (int i = 0; current_byte_index + i < m_lzw_bytes.size(); ++i) {
padded_last_bytes[i] = m_lzw_bytes[current_byte_index + i];
}
u32 const* addr = (u32 const*)&padded_last_bytes;
m_current_code = (*addr & mask) >> current_bit_offset;
} else {
u32 tmp_word;
memcpy(&tmp_word, &m_lzw_bytes.at(current_byte_index), sizeof(u32));
m_current_code = (tmp_word & mask) >> current_bit_offset;
}
m_current_code = TRY(m_bit_stream->read_bits<u16>(m_code_size));
if (m_current_code > m_code_table.size()) {
dbgln_if(GIF_DEBUG, "Corrupted LZW stream, invalid code: {} at bit index {}, code table size: {}",
dbgln_if(GIF_DEBUG, "Corrupted LZW stream, invalid code: {}, code table size: {}",
m_current_code,
m_current_bit_index,
m_code_table.size());
return Error::from_string_literal("Corrupted LZW stream, invalid code");
} else if (m_current_code == m_code_table.size() && m_output.is_empty()) {
dbgln_if(GIF_DEBUG, "Corrupted LZW stream, valid new code but output buffer is empty: {} at bit index {}, code table size: {}",
dbgln_if(GIF_DEBUG, "Corrupted LZW stream, valid new code but output buffer is empty: {}, code table size: {}",
m_current_code,
m_current_bit_index,
m_code_table.size());
return Error::from_string_literal("Corrupted LZW stream, valid new code but output buffer is empty");
}
m_current_bit_index += m_code_size;
return m_current_code;
}
@ -132,9 +107,7 @@ private:
}
}
Vector<u8> const& m_lzw_bytes;
int m_current_bit_index { 0 };
MaybeOwned<LittleEndianInputBitStream> m_bit_stream;
Vector<Vector<u8>> m_code_table {};
Vector<Vector<u8>> m_original_code_table {};

6
Userland/Libraries/LibGfx/ImageFormats/GIFLoader.cpp
View file

@ -6,6 +6,7 @@
*/
#include <AK/Array.h>
#include <AK/BitStream.h>
#include <AK/Debug.h>
#include <AK/Endian.h>
#include <AK/Error.h>
@ -183,7 +184,10 @@ static ErrorOr<void> decode_frame(GIFLoadingContext& context, size_t frame_index
if (image->lzw_min_code_size > 8)
return Error::from_string_literal("LZW minimum code size is greater than 8");
Compress::LZWDecoder decoder(image->lzw_encoded_bytes, image->lzw_min_code_size);
FixedMemoryStream stream { image->lzw_encoded_bytes, FixedMemoryStream::Mode::ReadOnly };
auto bit_stream = make<LittleEndianInputBitStream>(MaybeOwned<Stream>(stream));
Compress::LZWDecoder decoder(MaybeOwned<LittleEndianInputBitStream> { move(bit_stream) }, image->lzw_min_code_size);
// Add GIF-specific control codes
int const clear_code = decoder.add_control_code();