ladybird/Libraries/LibCompress/Zlib.cpp

/*
 * Copyright (c) 2020, the SerenityOS developers
 * All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
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 * 2. Redistributions in binary form must reproduce the above copyright notice,
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 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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#include <AK/Assertions.h>
#include <AK/Span.h>
#include <AK/Types.h>
#include <AK/Vector.h>
#include <LibCompress/Deflate.h>
#include <LibCompress/Zlib.h>

namespace Compress {

Zlib::Zlib(ReadonlyBytes data)
{
    m_input_data = data;

    u8 compression_info = data.at(0);
    u8 flags = data.at(1);

    m_compression_method = compression_info & 0xF;
    m_compression_info = (compression_info >> 4) & 0xF;
    m_check_bits = flags & 0xF;
    m_has_dictionary = (flags >> 5) & 0x1;
    m_compression_level = (flags >> 6) & 0x3;
    m_checksum = 0;

    ASSERT(m_compression_method == 8);
    ASSERT(m_compression_info == 7);
    ASSERT(!m_has_dictionary);
    ASSERT((compression_info * 256 + flags) % 31 == 0);

    m_data_bytes = data.slice(2, data.size() - 2 - 4);
}

Vector<u8> Zlib::decompress()
{
    return DeflateStream::decompress_all(m_data_bytes);
}

u32 Zlib::checksum()
{
    if (!m_checksum) {
        auto bytes = m_input_data.slice(m_input_data.size() - 4, 4);
        m_checksum = bytes.at(0) << 24 | bytes.at(1) << 16 | bytes.at(2) << 8 || bytes.at(3);
    }

    return m_checksum;
}

}