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Merge pull request #815 from TomHarte/WOZ2

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Support WOZ 2 disk images
This commit is contained in:
Thomas Harte 2020-07-19 23:22:55 -04:00 committed by GitHub
commit 9de43dac95
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4 changed files with 270 additions and 221 deletions
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71
Storage/Disk/DiskImage/Formats/WOZ.cpp
View File

@ -18,11 +18,21 @@ using namespace Storage::Disk;
WOZ::WOZ(const std::string &file_name) : WOZ::WOZ(const std::string &file_name) :
file_(file_name) { file_(file_name) {
const char signature[8] = { constexpr const char signature1[8] = {
'W', 'O', 'Z', '1', 'W', 'O', 'Z', '1',
char(0xff), 0x0a, 0x0d, 0x0a char(0xff), 0x0a, 0x0d, 0x0a
}; };
if(!file_.check_signature(signature, 8)) throw Error::InvalidFormat; constexpr const char signature2[8] = {
'W', 'O', 'Z', '2',
char(0xff), 0x0a, 0x0d, 0x0a
};
const bool isWoz1 = file_.check_signature(signature1, 8);
file_.seek(0, SEEK_SET);
const bool isWoz2 = file_.check_signature(signature2, 8);
if(!isWoz1 && !isWoz2) throw Error::InvalidFormat;
type_ = isWoz2 ? Type::WOZ2 : Type::WOZ1;
// Get the file's CRC32. // Get the file's CRC32.
const uint32_t crc = file_.get32le(); const uint32_t crc = file_.get32le();
@ -52,13 +62,22 @@ WOZ::WOZ(const std::string &file_name) :
switch(chunk_id) { switch(chunk_id) {
case CK("INFO"): { case CK("INFO"): {
const uint8_t version = file_.get8(); const uint8_t version = file_.get8();
if(version != 1) break; if(version > 2) break;
is_3_5_disk_ = file_.get8() == 2; is_3_5_disk_ = file_.get8() == 2;
is_read_only_ = file_.get8() == 1; is_read_only_ = file_.get8() == 1;
/* Ignored: /*
1 byte: Synchronized; 1 = Cross track sync was used during imaging. Ignored:
1 byte: Cleaned; 1 = MC3470 fake bits have been removed. 1 byte: Synchronized; 1 = Cross track sync was used during imaging.
32 bytes: Cretor; a UTF-8 string. 1 byte: Cleaned; 1 = MC3470 fake bits have been removed.
32 bytes: Creator; a UTF-8 string.
And, if version 2, following the creator:
1 byte number of disk sides
1 byte boot sector format
1 byte optimal bit timing
2 bytes compatible hardware
2 bytes minimum required RAM
2 bytes largest track
*/ */
} break; } break;
@ -99,11 +118,15 @@ long WOZ::file_offset(Track::Address address) {
if(track_map_[table_position] == 0xff) return NoSuchTrack; if(track_map_[table_position] == 0xff) return NoSuchTrack;
// Seek to the real track. // Seek to the real track.
return tracks_offset_ + track_map_[table_position] * 6656; switch(type_) {
case Type::WOZ1: return tracks_offset_ + track_map_[table_position] * 6656;
default:
case Type::WOZ2: return tracks_offset_ + track_map_[table_position] * 8;
}
} }
std::shared_ptr<Track> WOZ::get_track_at_position(Track::Address address) { std::shared_ptr<Track> WOZ::get_track_at_position(Track::Address address) {
long offset = file_offset(address); const long offset = file_offset(address);
if(offset == NoSuchTrack) return nullptr; if(offset == NoSuchTrack) return nullptr;
// Seek to the real track. // Seek to the real track.
@ -113,18 +136,34 @@ std::shared_ptr<Track> WOZ::get_track_at_position(Track::Address address) {
std::lock_guard lock_guard(file_.get_file_access_mutex()); std::lock_guard lock_guard(file_.get_file_access_mutex());
file_.seek(offset, SEEK_SET); file_.seek(offset, SEEK_SET);
// In WOZ a track is up to 6646 bytes of data, followed by a two-byte record of the switch(type_) {
// number of bytes that actually had data in them, then a two-byte count of the number case Type::WOZ1:
// of bits that were used. Other information follows but is not intended for emulation. // In WOZ 1, a track is up to 6646 bytes of data, followed by a two-byte record of the
track_contents = file_.read(6646); // number of bytes that actually had data in them, then a two-byte count of the number
file_.seek(2, SEEK_CUR); // of bits that were used. Other information follows but is not intended for emulation.
number_of_bits = std::min(file_.get16le(), uint16_t(6646*8)); track_contents = file_.read(6646);
file_.seek(2, SEEK_CUR);
number_of_bits = std::min(file_.get16le(), uint16_t(6646*8));
break;
case Type::WOZ2: {
// In WOZ 2 an extra level of indirection allows for variable track sizes.
const uint16_t starting_block = file_.get16le();
file_.seek(2, SEEK_CUR); // Skip the block count; the amount of data to read is implied by the number of bits.
number_of_bits = file_.get32le();
file_.seek(starting_block * 512, SEEK_SET);
track_contents = file_.read((number_of_bits + 7) >> 3);
} break;
}
} }
return std::make_shared<PCMTrack>(PCMSegment(number_of_bits, track_contents)); return std::make_shared<PCMTrack>(PCMSegment(number_of_bits, track_contents));
} }
void WOZ::set_tracks(const std::map<Track::Address, std::shared_ptr<Track>> &tracks) { void WOZ::set_tracks(const std::map<Track::Address, std::shared_ptr<Track>> &tracks) {
if(type_ == Type::WOZ2) return;
for(const auto &pair: tracks) { for(const auto &pair: tracks) {
// Decode the track and store, patching into the post_crc_contents_. // Decode the track and store, patching into the post_crc_contents_.
auto segment = Storage::Disk::track_serialisation(*pair.second, Storage::Time(1, 50000)); auto segment = Storage::Disk::track_serialisation(*pair.second, Storage::Time(1, 50000));
@ -155,5 +194,5 @@ void WOZ::set_tracks(const std::map<Track::Address, std::shared_ptr<Track>> &tra
} }
bool WOZ::get_is_read_only() { bool WOZ::get_is_read_only() {
return file_.get_is_known_read_only(); return file_.get_is_known_read_only() || is_read_only_ || type_ == Type::WOZ2; // WOZ 2 disks are currently read only.
} }

5
Storage/Disk/DiskImage/Formats/WOZ.hpp
View File

@ -34,6 +34,9 @@ class WOZ: public DiskImage {
private: private:
Storage::FileHolder file_; Storage::FileHolder file_;
enum class Type {
WOZ1, WOZ2
} type_ = Type::WOZ1;
bool is_read_only_ = false; bool is_read_only_ = false;
bool is_3_5_disk_ = false; bool is_3_5_disk_ = false;
uint8_t track_map_[160]; uint8_t track_map_[160];
@ -49,7 +52,7 @@ class WOZ: public DiskImage {
the track does not exit. the track does not exit.
*/ */
long file_offset(Track::Address address); long file_offset(Track::Address address);
constexpr static long NoSuchTrack = 0; // This is definitely an offset a track can't lie at. constexpr static long NoSuchTrack = 0; // This is an offset a track definitely can't lie at.
}; };
} }

26
Storage/Disk/Drive.cpp
View File

@ -250,6 +250,15 @@ void Drive::run_for(const Cycles cycles) {
// MARK: - Track timed event loop // MARK: - Track timed event loop
void Drive::get_next_event(float duration_already_passed) { void Drive::get_next_event(float duration_already_passed) {
/*
Quick word on random-bit generation logic below; it seeks to obey the following logic:
if there is a gap of 15µs between recorded bits, start generating flux transitions
at random intervals thereafter, unless and until one is within 5µs of the next real transition.
This behaviour is based on John Morris' observations of an MC3470, as described in his WOZ
file format documentation — https://applesaucefdc.com/woz/reference2/
*/
if(!disk_) { if(!disk_) {
current_event_.type = Track::Event::IndexHole; current_event_.type = Track::Event::IndexHole;
current_event_.length = 1.0f; current_event_.length = 1.0f;
@ -268,17 +277,18 @@ void Drive::get_next_event(float duration_already_passed) {
// If gain has now been turned up so as to generate noise, generate some noise. // If gain has now been turned up so as to generate noise, generate some noise.
if(random_interval_ > 0.0f) { if(random_interval_ > 0.0f) {
current_event_.type = Track::Event::FluxTransition; current_event_.type = Track::Event::FluxTransition;
current_event_.length = float(2 + (random_source_&1)) / 1000000.0f; current_event_.length = float(2 + (random_source_&1)) / 1'000'000.0f;
random_source_ = (random_source_ >> 1) | (random_source_ << 63); random_source_ = (random_source_ >> 1) | (random_source_ << 63);
if(random_interval_ < current_event_.length) { // If this random transition is closer than 5µs to the next real bit,
current_event_.length = random_interval_; // discard it.
if(random_interval_ - 5.0f / 1'000'000.f < current_event_.length) {
random_interval_ = 0.0f; random_interval_ = 0.0f;
} else { } else {
random_interval_ -= current_event_.length; random_interval_ -= current_event_.length;
set_next_event_time_interval(current_event_.length);
return;
} }
set_next_event_time_interval(current_event_.length);
return;
} }
if(track_) { if(track_) {
@ -299,9 +309,9 @@ void Drive::get_next_event(float duration_already_passed) {
// convert it into revolutions per second; this is achieved by multiplying by rotational_multiplier_ // convert it into revolutions per second; this is achieved by multiplying by rotational_multiplier_
float interval = std::max((current_event_.length - duration_already_passed) * rotational_multiplier_, 0.0f); float interval = std::max((current_event_.length - duration_already_passed) * rotational_multiplier_, 0.0f);
// An interval greater than 15ms => adjust gain up the point where noise starts happening. // An interval greater than 15µs => adjust gain up the point where noise starts happening.
// Seed that up and leave a 15ms gap until it starts. // Seed that up and leave a 15µs gap until it starts.
constexpr float safe_gain_period = 15.0f / 1000000.0f; constexpr float safe_gain_period = 15.0f / 1'000'000.0f;
if(interval >= safe_gain_period) { if(interval >= safe_gain_period) {
random_interval_ = interval - safe_gain_period; random_interval_ = interval - safe_gain_period;
interval = safe_gain_period; interval = safe_gain_period;

389
Storage/Disk/Encodings/AppleGCR/SegmentParser.cpp
View File

@ -12,6 +12,8 @@
#include <array> #include <array>
using namespace Storage::Encodings::AppleGCR;
namespace { namespace {
const uint8_t six_and_two_unmapping[] = { const uint8_t six_and_two_unmapping[] = {
@ -55,9 +57,181 @@ uint8_t unmap_five_and_three(uint8_t source) {
return five_and_three_unmapping[source - 0xab]; return five_and_three_unmapping[source - 0xab];
} }
std::unique_ptr<Sector> decode_macintosh_sector(const std::array<uint_fast8_t, 8> &header, const std::unique_ptr<Sector> &original) {
// There must be at least 704 bytes to decode from.
if(original->data.size() < 704) return nullptr;
// Attempt a six-and-two unmapping of the header.
std::array<uint_fast8_t, 5> decoded_header;
for(size_t c = 0; c < decoded_header.size(); ++c) {
decoded_header[c] = unmap_six_and_two(header[c]);
if(decoded_header[c] == 0xff) {
return nullptr;
}
}
// Allocate a sector.
auto sector = std::make_unique<Sector>();
sector->data.resize(704);
// Test the checksum.
if(decoded_header[4] != (decoded_header[0] ^ decoded_header[1] ^ decoded_header[2] ^ decoded_header[3]))
sector->has_header_checksum_error = true;
// Decode the header.
sector->address.track = uint8_t(decoded_header[0] | ((decoded_header[2]&0x1f) << 6));
sector->address.sector = decoded_header[1];
sector->address.format = decoded_header[3];
sector->address.is_side_two = decoded_header[2] & 0x20;
// Reverse the GCR encoding of the sector contents to get back to 6-bit data.
for(size_t index = 0; index < sector->data.size(); ++index) {
sector->data[index] = unmap_six_and_two(original->data[index]);
if(sector->data[index] == 0xff) {
return nullptr;
}
}
// The first byte in the sector is a repeat of the sector number; test it
// for correctness.
if(sector->data[0] != sector->address.sector) {
return nullptr;
}
// Cf. the corresponding section of Encoder.cpp for logic below.
int checksum[3] = {0, 0, 0};
for(size_t c = 0; c < 175; ++c) {
// Calculate the rolling checcksum in order to decode the bytes.
checksum[0] = (checksum[0] << 1) | (checksum[0] >> 7);
// All offsets are +1 below, to skip the initial sector number duplicate.
const uint8_t top_bits = sector->data[1 + c*4];
// Decode first byte.
sector->data[0 + c * 3] = uint8_t((sector->data[2 + c*4] + ((top_bits & 0x30) << 2)) ^ checksum[0]);
checksum[2] += sector->data[0 + c * 3] + (checksum[0] >> 8);
// Decode second byte;
sector->data[1 + c * 3] = uint8_t((sector->data[3 + c*4] + ((top_bits & 0x0c) << 4)) ^ checksum[2]);
checksum[1] += sector->data[1 + c * 3] + (checksum[2] >> 8);
// Decode third byte, if there is one.
if(c != 174) {
sector->data[2 + c * 3] = uint8_t((sector->data[4 + c*4] + ((top_bits & 0x03) << 6)) ^ checksum[1]);
checksum[0] += sector->data[2 + c * 3] + (checksum[1] >> 8);
}
// Reset carries.
checksum[0] &= 0xff;
checksum[1] &= 0xff;
checksum[2] &= 0xff;
}
// Test the checksum.
if(
checksum[0] != uint8_t(sector->data[703] + ((sector->data[700] & 0x03) << 6)) ||
checksum[1] != uint8_t(sector->data[702] + ((sector->data[700] & 0x0c) << 4)) ||
checksum[2] != uint8_t(sector->data[701] + ((sector->data[700] & 0x30) << 2))
) sector->has_data_checksum_error = true;
// Report success.
sector->data.resize(524);
sector->encoding = Sector::Encoding::Macintosh;
return sector;
} }
using namespace Storage::Encodings::AppleGCR; std::unique_ptr<Sector> decode_appleii_sector(const std::array<uint_fast8_t, 8> &header, const std::unique_ptr<Sector> &original, bool is_five_and_three) {
// There must be at least 411 bytes to decode a five-and-three sector from;
// there must be only 343 if this is a six-and-two sector.
const size_t data_size = is_five_and_three ? 411 : 343;
if(original->data.size() < data_size) return nullptr;
// Check for apparent four and four encoding.
uint_fast8_t header_mask = 0xff;
for(auto c : header) header_mask &= c;
header_mask &= 0xaa;
if(header_mask != 0xaa) return nullptr;
// Allocate a sector and fill the header fields.
auto sector = std::make_unique<Sector>();
sector->data.resize(data_size);
sector->address.volume = ((header[0] << 1) | 1) & header[1];
sector->address.track = ((header[2] << 1) | 1) & header[3];
sector->address.sector = ((header[4] << 1) | 1) & header[5];
// Check the header checksum.
const uint_fast8_t checksum = ((header[6] << 1) | 1) & header[7];
if(checksum != (sector->address.volume^sector->address.track^sector->address.sector)) return nullptr;
// Unmap the sector contents.
for(size_t index = 0; index < data_size; ++index) {
sector->data[index] = is_five_and_three ? unmap_five_and_three(original->data[index]) : unmap_six_and_two(original->data[index]);
if(sector->data[index] == 0xff) {
return nullptr;
}
}
// Undo the XOR step on sector contents and check that checksum.
for(std::size_t c = 1; c < sector->data.size(); ++c) {
sector->data[c] ^= sector->data[c-1];
}
if(sector->data.back()) return nullptr;
// Having checked the checksum, remove it.
sector->data.resize(sector->data.size() - 1);
if(is_five_and_three) {
// TODO: the below is almost certainly incorrect; Beneath Apple DOS partly documents
// the process, enough to give the basic outline below of how five source bytes are
// mapped to eight five-bit quantities, but isn't clear on the order those bytes will
// end up in on disk.
std::vector<uint8_t> buffer(256);
for(size_t c = 0; c < 0x33; ++c) {
const uint8_t *const base = &sector->data[0x032 - c];
buffer[(c * 5) + 0] = uint8_t((base[0x000] << 3) | (base[0x100] >> 2));
buffer[(c * 5) + 1] = uint8_t((base[0x033] << 3) | (base[0x133] >> 2));
buffer[(c * 5) + 2] = uint8_t((base[0x066] << 3) | (base[0x166] >> 2));
buffer[(c * 5) + 3] = uint8_t((base[0x099] << 3) | ((base[0x100] & 2) << 1) | (base[0x133] & 2) | ((base[0x166] & 2) >> 1));
buffer[(c * 5) + 4] = uint8_t((base[0x0cc] << 3) | ((base[0x100] & 1) << 2) | ((base[0x133] & 1) << 1) | (base[0x166] & 1));
}
buffer[255] = uint8_t((sector->data[0x0ff] << 3) | (sector->data[0x199] >> 2));
sector->data = std::move(buffer);
sector->encoding = Sector::Encoding::FiveAndThree;
} else {
// Undo the 6 and 2 mapping.
constexpr uint8_t bit_reverse[] = {0, 2, 1, 3};
#define unmap(byte, nibble, shift) \
sector->data[86 + byte] = uint8_t(\
(sector->data[86 + byte] << 2) | bit_reverse[(sector->data[nibble] >> shift)&3]);
for(std::size_t c = 0; c < 84; ++c) {
unmap(c, c, 0);
unmap(c+86, c, 2);
unmap(c+172, c, 4);
}
unmap(84, 84, 0);
unmap(170, 84, 2);
unmap(85, 85, 0);
unmap(171, 85, 2);
#undef unmap
// Throw away the collection of two-bit chunks from the start of the sector.
sector->data.erase(sector->data.begin(), sector->data.end() - 256);
sector->encoding = Sector::Encoding::SixAndTwo;
}
// Return successfully.
return sector;
}
}
std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment(const Disk::PCMSegment &segment) { std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment(const Disk::PCMSegment &segment) {
std::map<std::size_t, Sector> result; std::map<std::size_t, Sector> result;
@ -112,7 +286,7 @@ std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment
if(scanner[2] == data_prologue[2]) { if(scanner[2] == data_prologue[2]) {
new_sector = std::make_unique<Sector>(); new_sector = std::make_unique<Sector>();
new_sector->data.reserve(710); new_sector->data.reserve(710);
} else { } else { // i.e. the third symbol is from either of the header prologues.
sector_location = size_t(bit % segment.data.size()); sector_location = size_t(bit % segment.data.size());
header_delay = 200; // Allow up to 200 bytes to find the body, if the header_delay = 200; // Allow up to 200 bytes to find the body, if the
// track split comes in between. // track split comes in between.
@ -120,23 +294,12 @@ std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment
} }
} else { } else {
if(new_sector) { if(new_sector) {
// Check whether the value just read is a legal GCR byte, in six-and-two // Check whether the value just read is a legal GCR byte, for this sector;
// encoding (which is a strict superset of five-and-three). // if not, or if
const bool is_invalid = is_five_and_three ? (unmap_five_and_three(value) == 0xff) : (unmap_six_and_two(value) == 0xff); const bool is_invalid = is_five_and_three ? (unmap_five_and_three(value) == 0xff) : (unmap_six_and_two(value) == 0xff);
if(is_invalid) { if(is_invalid || new_sector->data.size() >= 704) {
// The second byte of the standard epilogue is illegal, so this still may // The second byte of the standard epilogue is 'illegal', as is the first byte of
// be a valid sector. If the final byte was the first byte of an epilogue, // all prologues. So either a whole sector has been captured up to now, or it hasn't.
// chop it off and see whether the sector is otherwise intelligible.
if(new_sector->data.empty() || new_sector->data.back() != epilogue[0]) {
// No sector found; reset scanning procedure.
new_sector.reset();
pointer = scanning_sentinel;
continue;
}
// Chop off the last byte.
new_sector->data.resize(new_sector->data.size() - 1);
// Move the sector elsewhere for processing; there's definitely no way to proceed with // Move the sector elsewhere for processing; there's definitely no way to proceed with
// the prospective sector if it doesn't parse. // the prospective sector if it doesn't parse.
@ -144,185 +307,19 @@ std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment
new_sector.reset(); new_sector.reset();
pointer = scanning_sentinel; pointer = scanning_sentinel;
// Check for valid decoding options. // Potentially this is a Macintosh sector.
switch(sector->data.size()) { auto macintosh_sector = decode_macintosh_sector(header, sector);
default: // This is not a decodeable sector. if(macintosh_sector) {
break; result.insert(std::make_pair(sector_location, std::move(*macintosh_sector)));
continue;
case 411: // Potentially this is an Apple II five-and-three sector.
case 343: { // Potentially this is an Apple II six-and-two sector.
// Check for apparent four and four encoding.
uint_fast8_t header_mask = 0xff;
for(auto c : header) header_mask &= c;
header_mask &= 0xaa;
if(header_mask != 0xaa) continue;
sector->address.volume = ((header[0] << 1) | 1) & header[1];
sector->address.track = ((header[2] << 1) | 1) & header[3];
sector->address.sector = ((header[4] << 1) | 1) & header[5];
// Check the header checksum.
// The 0x11 is reverse engineered from the game 'Alien Rain' and is present even on the boot sector,
// so probably isn't copy protection?
uint_fast8_t checksum = (((header[6] << 1) | 1) & header[7]) ^ (is_five_and_three ? 0x11 : 0x00);
if(checksum != (sector->address.volume^sector->address.track^sector->address.sector)) continue;
// Unmap the sector contents.
bool out_of_bounds = false;
for(auto &c : sector->data) {
c = is_five_and_three ? unmap_five_and_three(c) : unmap_six_and_two(c);
if(c == 0xff) {
out_of_bounds = true;
break;
}
}
if(out_of_bounds) continue;
// Undo the XOR step on sector contents and check that checksum.
for(std::size_t c = 1; c < sector->data.size(); ++c) {
sector->data[c] ^= sector->data[c-1];
}
if(sector->data.back()) continue;
// Having checked the checksum, remove it.
sector->data.resize(sector->data.size() - 1);
if(is_five_and_three) {
// TODO: the above is almost certainly incorrect; Beneath Apple DOS partly documents
// the process, enough to give the basic outline below of how five source bytes are
// mapped to eight five-bit quantities, but isn't clear on the order those bytes will
// end up in on disk.
std::vector<uint8_t> buffer(256);
for(size_t c = 0; c < 0x33; ++c) {
const uint8_t *const base = &sector->data[0x032 - c];
buffer[(c * 5) + 0] = uint8_t((base[0x000] << 3) | (base[0x100] >> 2));
buffer[(c * 5) + 1] = uint8_t((base[0x033] << 3) | (base[0x133] >> 2));
buffer[(c * 5) + 2] = uint8_t((base[0x066] << 3) | (base[0x166] >> 2));
buffer[(c * 5) + 3] = uint8_t((base[0x099] << 3) | ((base[0x100] & 2) << 1) | (base[0x133] & 2) | ((base[0x166] & 2) >> 1));
buffer[(c * 5) + 4] = uint8_t((base[0x0cc] << 3) | ((base[0x100] & 1) << 2) | ((base[0x133] & 1) << 1) | (base[0x166] & 1));
}
buffer[255] = uint8_t((sector->data[0x0ff] << 3) | (sector->data[0x199] >> 2));
sector->data = std::move(buffer);
sector->encoding = Sector::Encoding::FiveAndThree;
} else {
// Undo the 6 and 2 mapping.
const uint8_t bit_reverse[] = {0, 2, 1, 3};
#define unmap(byte, nibble, shift) \
sector->data[86 + byte] = uint8_t(\
(sector->data[86 + byte] << 2) | bit_reverse[(sector->data[nibble] >> shift)&3]);
for(std::size_t c = 0; c < 84; ++c) {
unmap(c, c, 0);
unmap(c+86, c, 2);
unmap(c+172, c, 4);
}
unmap(84, 84, 0);
unmap(170, 84, 2);
unmap(85, 85, 0);
unmap(171, 85, 2);
#undef unmap
// Throw away the collection of two-bit chunks from the start of the sector.
sector->data.erase(sector->data.begin(), sector->data.end() - 256);
sector->encoding = Sector::Encoding::SixAndTwo;
}
// Add this sector to the map.
result.insert(std::make_pair(sector_location, std::move(*sector)));
} break;
case 704: { // Potentially this is a Macintosh sector.
// Attempt a six-and-two unmapping of the header.
std::array<uint_fast8_t, 5> decoded_header;
bool out_of_bounds = false;
for(size_t c = 0; c < decoded_header.size(); ++c) {
decoded_header[c] = unmap_six_and_two(header[c]);
if(decoded_header[c] == 0xff) {
out_of_bounds = true;
break;
}
}
if(out_of_bounds) {
continue;
}
// Test the checksum.
if(decoded_header[4] != (decoded_header[0] ^ decoded_header[1] ^ decoded_header[2] ^ decoded_header[3]))
sector->has_header_checksum_error = true;
// Decode the header.
sector->address.track = uint8_t(decoded_header[0] | ((decoded_header[2]&0x1f) << 6));
sector->address.sector = decoded_header[1];
sector->address.format = decoded_header[3];
sector->address.is_side_two = decoded_header[2] & 0x20;
// Reverse the GCR encoding of the sector contents to get back to 6-bit data.
for(auto &c: sector->data) {
c = unmap_six_and_two(c);
if(c == 0xff) {
out_of_bounds = true;
break;
}
}
if(out_of_bounds) {
continue;
}
// The first byte in the sector is a repeat of the sector number; test it
// for correctness.
if(sector->data[0] != sector->address.sector) {
continue;
}
// Cf. the corresponding section of Encoder.cpp for logic below.
int checksum[3] = {0, 0, 0};
for(size_t c = 0; c < 175; ++c) {
// Calculate the rolling checcksum in order to decode the bytes.
checksum[0] = (checksum[0] << 1) | (checksum[0] >> 7);
// All offsets are +1 below, to skip the initial sector number duplicate.
const uint8_t top_bits = sector->data[1 + c*4];
// Decode first byte.
sector->data[0 + c * 3] = uint8_t((sector->data[2 + c*4] + ((top_bits & 0x30) << 2)) ^ checksum[0]);
checksum[2] += sector->data[0 + c * 3] + (checksum[0] >> 8);
// Decode second byte;
sector->data[1 + c * 3] = uint8_t((sector->data[3 + c*4] + ((top_bits & 0x0c) << 4)) ^ checksum[2]);
checksum[1] += sector->data[1 + c * 3] + (checksum[2] >> 8);
// Decode third byte, if there is one.
if(c != 174) {
sector->data[2 + c * 3] = uint8_t((sector->data[4 + c*4] + ((top_bits & 0x03) << 6)) ^ checksum[1]);
checksum[0] += sector->data[2 + c * 3] + (checksum[1] >> 8);
}
// Reset carries.
checksum[0] &= 0xff;
checksum[1] &= 0xff;
checksum[2] &= 0xff;
}
// Test the checksum.
if(
checksum[0] != uint8_t(sector->data[703] + ((sector->data[700] & 0x03) << 6)) ||
checksum[1] != uint8_t(sector->data[702] + ((sector->data[700] & 0x0c) << 4)) ||
checksum[2] != uint8_t(sector->data[701] + ((sector->data[700] & 0x30) << 2))
) sector->has_data_checksum_error = true;
// Chop to size, and that's that.
sector->data.resize(524);
// Add this sector to the map.
sector->encoding = Sector::Encoding::Macintosh;
result.insert(std::make_pair(sector_location, std::move(*sector)));
} break;
} }
// Apple II then?
auto appleii_sector = decode_appleii_sector(header, sector, is_five_and_three);
if(appleii_sector) {
result.insert(std::make_pair(sector_location, std::move(*appleii_sector)));
}
} else { } else {
new_sector->data.push_back(value); new_sector->data.push_back(value);
} }