fluxengine/lib/imagereader/td0imagereader.cc

#include "globals.h"
#include "flags.h"
#include "sector.h"
#include "imagereader/imagereader.h"
#include "image.h"
#include "crc.h"
#include "logger.h"
#include "lib/config.pb.h"
#include <algorithm>
#include <iostream>
#include <fstream>

/* The best description of the Teledisk format I've found is available here:
 *
 * https://web.archive.org/web/20210420230238/http://dunfield.classiccmp.org/img47321/td0notes.txt
 *
 * Header:
 *
 * Signature                   (2 bytes); TD for normal, td for compressed
 * Sequence                    (1 byte)
 * Checksequence               (1 byte)
 * Teledisk version            (1 byte)
 * Data rate                   (1 byte)
 * Drive type                  (1 byte)
 * Stepping                    (1 byte)
 * DOS allocation flag         (1 byte)
 * Sides                       (1 byte)
 * Cyclic Redundancy Check     (2 bytes)
 */

enum
{
    TD0_ENCODING_RAW = 0,
    TD0_ENCODING_REPEATED = 1,
    TD0_ENCODING_RLE = 2,

    TD0_FLAG_DUPLICATE = 0x01,
    TD0_FLAG_CRC_ERROR = 0x02,
    TD0_FLAG_DELETED = 0x04,
    TD0_FLAG_SKIPPED = 0x10,
    TD0_FLAG_IDNODATA = 0x20,
    TD0_FLAG_DATANOID = 0x40,
};

class Td0ImageReader : public ImageReader
{
public:
    Td0ImageReader(const ImageReaderProto& config): ImageReader(config) {}

    std::unique_ptr<Image> readImage()
    {
        std::ifstream inputFile(
            _config.filename(), std::ios::in | std::ios::binary);
        if (!inputFile.is_open())
            error("cannot open input file");

        Bytes input;
        input.writer() += inputFile;
        ByteReader br(input);

        uint16_t signature = br.read_be16();
        br.skip(2); /* sequence and checksequence */
        uint8_t version = br.read_8();
        br.skip(2); /* data rate, drive type */
        uint8_t stepping = br.read_8();
        br.skip(1); /* sparse flag */
        uint8_t sides = (br.read_8() == 1) ? 1 : 2;
        uint16_t headerCrc = br.read_le16();

        uint16_t gotCrc = crc16(0xa097, 0, input.slice(0, 10));
        if (gotCrc != headerCrc)
            error("TD0: header checksum mismatch");
        if (signature != 0x5444)
            error(
                "TD0: unsupported file type (only uncompressed files "
                "are supported for now)");

        std::string comment = "(no comment)";
        if (stepping & 0x80)
        {
            /* Comment block */

            br.skip(2); /* comment CRC */
            uint16_t length = br.read_le16();
            br.skip(6); /* timestamp */
            comment = br.read(length);
            std::replace(comment.begin(), comment.end(), '\0', '\n');

            /* Strip trailing newlines */

            auto nl = std::find_if(comment.rbegin(),
                comment.rend(),
                [](unsigned char ch)
                {
                    return !std::isspace(ch);
                });
            comment.erase(nl.base(), comment.end());
        }

        log("TD0: TeleDisk {}.{}: {}", version / 10, version % 10, comment);

        unsigned totalSize = 0;
        std::unique_ptr<Image> image(new Image);
        for (;;)
        {
            /* Read track header */

            uint8_t sectorCount = br.read_8();
            if (sectorCount == 0xff)
                break;

            uint8_t physicalTrack = br.read_8();
            uint8_t physicalSide = br.read_8() & 1;
            br.skip(1); /* crc */

            for (int i = 0; i < sectorCount; i++)
            {
                /* Read sector */

                uint8_t logicalTrack = br.read_8();
                uint8_t logicalSide = br.read_8();
                uint8_t sectorId = br.read_8();
                uint8_t sectorSizeEncoded = br.read_8();
                unsigned sectorSize = 128 << sectorSizeEncoded;
                uint8_t flags = br.read_8();
                br.skip(1); /* CRC */

                uint16_t dataSize = br.read_le16();
                Bytes encodedData = br.read(dataSize);
                ByteReader bre(encodedData);
                uint8_t encoding = bre.read_8();

                Bytes data;
                if (!(flags & (TD0_FLAG_SKIPPED | TD0_FLAG_IDNODATA)))
                {
                    switch (encoding)
                    {
                        case TD0_ENCODING_RAW:
                            data = encodedData.slice(1);
                            break;

                        case TD0_ENCODING_REPEATED:
                        {
                            ByteWriter bw(data);
                            while (!bre.eof())
                            {
                                uint16_t pattern = bre.read_le16();
                                uint16_t count = bre.read_le16();
                                while (count--)
                                    bw.write_le16(pattern);
                            }
                            break;
                        }

                        case TD0_ENCODING_RLE:
                        {
                            ByteWriter bw(data);
                            while (!bre.eof())
                            {
                                uint8_t length = bre.read_8() * 2;
                                if (length == 0)
                                {
                                    /* Literal block */

                                    length = bre.read_8();
                                    bw += bre.read(length);
                                }
                                else
                                {
                                    /* Repeated block */

                                    uint8_t count = bre.read_8();
                                    Bytes b = bre.read(length);
                                    while (count--)
                                        bw += b;
                                }
                            }
                            break;
                        }
                    }
                }

                const auto& sector =
                    image->put(logicalTrack, logicalSide, sectorId);
                sector->status = Sector::OK;
                sector->physicalTrack = physicalTrack;
                sector->physicalSide = physicalSide;
                sector->data = data.slice(0, sectorSize);
                totalSize += sectorSize;
            }
        }

        image->calculateSize();
        const Geometry& geometry = image->getGeometry();
        log("TD0: found {} tracks, {} sides, {} sectors, {} bytes per sector, "
            "{} kB total",
            geometry.numTracks,
            geometry.numSides,
            geometry.numSectors,
            geometry.sectorSize,
            totalSize / 1024);
        return image;
    }
};

std::unique_ptr<ImageReader> ImageReader::createTd0ImageReader(
    const ImageReaderProto& config)
{
    return std::unique_ptr<ImageReader>(new Td0ImageReader(config));
}