serenity/AK/BitStream.h

/*
 * Copyright (c) 2020, the SerenityOS developers.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <AK/Optional.h>
#include <AK/Stream.h>

namespace AK {

class InputBitStream final : public InputStream {
public:
    explicit InputBitStream(InputStream& stream)
        : m_stream(stream)
    {
    }

    size_t read(Bytes bytes) override
    {
        size_t nread = 0;

        if (bytes.size() >= 1) {
            if (m_next_byte.has_value()) {
                bytes[0] = m_next_byte.value();
                m_next_byte.clear();

                ++nread;
            }
        }

        return nread + m_stream.read(bytes.slice(nread));
    }

    bool read_or_error(Bytes bytes) override
    {
        if (read(bytes) != bytes.size()) {
            set_fatal_error();
            return false;
        }

        return true;
    }

    bool eof() const override { return !m_next_byte.has_value() && m_stream.eof(); }

    bool discard_or_error(size_t count) override
    {
        if (count >= 1) {
            if (m_next_byte.has_value()) {
                m_next_byte.clear();
                --count;
            }
        }

        return discard_or_error(count);
    }

    u32 read_bits(size_t count)
    {
        u32 result = 0;

        size_t nread = 0;
        while (nread < count) {
            if (m_next_byte.has_value()) {
                const auto bit = (m_next_byte.value() >> m_bit_offset) & 1;
                result |= bit << nread;
                ++nread;

                if (m_bit_offset++ == 7)
                    m_next_byte.clear();
            } else if (m_stream.eof()) {
                set_fatal_error();
                return 0;
            } else {
                m_stream >> m_next_byte;
                m_bit_offset = 0;
            }
        }

        return result;
    }

    bool read_bit() { return static_cast<bool>(read_bits(1)); }

    void align_to_byte_boundary()
    {
        if (m_next_byte.has_value())
            m_next_byte.clear();
    }

private:
    Optional<u8> m_next_byte;
    size_t m_bit_offset { 0 };
    InputStream& m_stream;
};

}

using AK::InputBitStream;