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Makes a first attempt at six-and-two encoding for DSKs.

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This commit is contained in:
Thomas Harte 2018-04-28 15:18:48 -04:00
parent b98d5b790a
commit 7f03f5d02f
3 changed files with 127 additions and 61 deletions
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28
Storage/Disk/DiskImage/Formats/AppleDSK.cpp
View File

@ -8,6 +8,9 @@
#include "AppleDSK.hpp"
#include "../../Track/PCMTrack.hpp"
#include "../../Encodings/AppleGCR.hpp"
using namespace Storage::Disk;
namespace {
@ -30,8 +33,29 @@ int AppleDSK::get_head_position_count() {
std::shared_ptr<Track> AppleDSK::get_track_at_position(Track::Address address) {
const long file_offset = (address.position >> 2) * bytes_per_sector * sectors_per_track_;
file_.seek(file_offset, SEEK_SET);
const std::vector<uint8_t> track_data = file_.read(static_cast<size_t>(bytes_per_sector * sectors_per_track_));
// std::vector<uint8_t> track_data = file_.read(bytes_per_sector * sectors_per_track_);
std::vector<Storage::Disk::PCMSegment> segments;
const uint8_t track = static_cast<uint8_t>(address.position >> 2);
return nullptr;
// In either case below, the code aims for exactly 50,000 bits per track.
if(sectors_per_track_ == 16) {
// Write the sectors.
for(uint8_t c = 0; c < 16; ++c) {
segments.push_back(Encodings::AppleGCR::six_and_two_sync(10));
segments.push_back(Encodings::AppleGCR::header(0, track, c));
segments.push_back(Encodings::AppleGCR::six_and_two_sync(10));
segments.push_back(Encodings::AppleGCR::six_and_two_data(&track_data[c * 256]));
segments.push_back(Encodings::AppleGCR::six_and_two_sync(10));
}
int encoded_length = (80 + 112 + 80 + 2848 + 80) * sectors_per_track_;
segments.push_back(Encodings::AppleGCR::six_and_two_sync((50000 - encoded_length) >> 3));
} else {
}
return std::shared_ptr<PCMTrack>(new PCMTrack(segments));
}

144
Storage/Disk/Encodings/AppleGCR.cpp
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@ -8,55 +8,31 @@
#include "AppleGCR.hpp"
using namespace Storage::Encodings;
namespace {
unsigned int AppleGCR::five_and_three_encoding_for_value(int value) {
static const unsigned int values[] = {
0xab, 0xad, 0xae, 0xaf, 0xb5, 0xb6, 0xb7, 0xba,
0xbb, 0xbd, 0xbe, 0xbf, 0xd6, 0xd7, 0xda, 0xdb,
0xdd, 0xde, 0xdf, 0xea, 0xeb, 0xed, 0xee, 0xef,
0xf5, 0xf6, 0xf7, 0xfa, 0xfb, 0xfd, 0xfe, 0xff
};
return values[value & 0x1f];
}
const unsigned int five_and_three_mapping[] = {
0xab, 0xad, 0xae, 0xaf, 0xb5, 0xb6, 0xb7, 0xba,
0xbb, 0xbd, 0xbe, 0xbf, 0xd6, 0xd7, 0xda, 0xdb,
0xdd, 0xde, 0xdf, 0xea, 0xeb, 0xed, 0xee, 0xef,
0xf5, 0xf6, 0xf7, 0xfa, 0xfb, 0xfd, 0xfe, 0xff
};
void AppleGCR::encode_five_and_three_block(uint8_t *destination, uint8_t *source) {
destination[0] = static_cast<uint8_t>(five_and_three_encoding_for_value( source[0] >> 3 ));
destination[1] = static_cast<uint8_t>(five_and_three_encoding_for_value( (source[0] << 2) | (source[1] >> 6) ));
destination[2] = static_cast<uint8_t>(five_and_three_encoding_for_value( source[1] >> 1 ));
destination[3] = static_cast<uint8_t>(five_and_three_encoding_for_value( (source[1] << 4) | (source[2] >> 4) ));
destination[4] = static_cast<uint8_t>(five_and_three_encoding_for_value( (source[2] << 1) | (source[3] >> 7) ));
destination[5] = static_cast<uint8_t>(five_and_three_encoding_for_value( source[3] >> 2 ));
destination[6] = static_cast<uint8_t>(five_and_three_encoding_for_value( (source[3] << 3) | (source[4] >> 5) ));
destination[7] = static_cast<uint8_t>(five_and_three_encoding_for_value( source[4] ));
}
unsigned int AppleGCR::six_and_two_encoding_for_value(int value) {
static const unsigned int values[] = {
0x96, 0x97, 0x9a, 0x9b, 0x9d, 0x9e, 0x9f, 0xa6,
0xa7, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb2, 0xb3,
0xb4, 0xb5, 0xb6, 0xb7, 0xb9, 0xba, 0xbb, 0xbc,
0xbd, 0xbe, 0xbf, 0xcb, 0xcd, 0xce, 0xcf, 0xd3,
0xd6, 0xd7, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde,
0xdf, 0xe5, 0xe6, 0xe7, 0xe9, 0xea, 0xeb, 0xec,
0xed, 0xee, 0xef, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6,
0xf7, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
};
return values[value & 0x3f];
}
void AppleGCR::encode_six_and_two_block(uint8_t *destination, uint8_t *source) {
destination[0] = static_cast<uint8_t>(six_and_two_encoding_for_value( source[0] >> 2 ));
destination[1] = static_cast<uint8_t>(six_and_two_encoding_for_value( (source[0] << 4) | (source[1] >> 4) ));
destination[2] = static_cast<uint8_t>(six_and_two_encoding_for_value( (source[1] << 2) | (source[2] >> 6) ));
destination[3] = static_cast<uint8_t>(six_and_two_encoding_for_value( source[2] ));
}
const uint8_t six_and_two_mapping[] = {
0x96, 0x97, 0x9a, 0x9b, 0x9d, 0x9e, 0x9f, 0xa6,
0xa7, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb2, 0xb3,
0xb4, 0xb5, 0xb6, 0xb7, 0xb9, 0xba, 0xbb, 0xbc,
0xbd, 0xbe, 0xbf, 0xcb, 0xcd, 0xce, 0xcf, 0xd3,
0xd6, 0xd7, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde,
0xdf, 0xe5, 0xe6, 0xe7, 0xe9, 0xea, 0xeb, 0xec,
0xed, 0xee, 0xef, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6,
0xf7, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
};
/*!
Produces a PCM segment containing @c length sync bytes, each aligned to the beginning of
a @c bit_size -sized window.
*/
static Storage::Disk::PCMSegment sync(int length, int bit_size) {
Storage::Disk::PCMSegment sync(int length, int bit_size) {
Storage::Disk::PCMSegment segment;
// Allocate sufficient storage.
@ -73,6 +49,30 @@ static Storage::Disk::PCMSegment sync(int length, int bit_size) {
return segment;
}
}
using namespace Storage::Encodings;
/*void AppleGCR::encode_five_and_three_block(uint8_t *destination, uint8_t *source) {
destination[0] = static_cast<uint8_t>(five_and_three_encoding_for_value( source[0] >> 3 ));
destination[1] = static_cast<uint8_t>(five_and_three_encoding_for_value( (source[0] << 2) | (source[1] >> 6) ));
destination[2] = static_cast<uint8_t>(five_and_three_encoding_for_value( source[1] >> 1 ));
destination[3] = static_cast<uint8_t>(five_and_three_encoding_for_value( (source[1] << 4) | (source[2] >> 4) ));
destination[4] = static_cast<uint8_t>(five_and_three_encoding_for_value( (source[2] << 1) | (source[3] >> 7) ));
destination[5] = static_cast<uint8_t>(five_and_three_encoding_for_value( source[3] >> 2 ));
destination[6] = static_cast<uint8_t>(five_and_three_encoding_for_value( (source[3] << 3) | (source[4] >> 5) ));
destination[7] = static_cast<uint8_t>(five_and_three_encoding_for_value( source[4] ));
}*/
/*void AppleGCR::encode_six_and_two_block(uint8_t *destination, uint8_t *source) {
destination[0] = static_cast<uint8_t>(six_and_two_encoding_for_value( source[0] >> 2 ));
destination[1] = static_cast<uint8_t>(six_and_two_encoding_for_value( (source[0] << 4) | (source[1] >> 4) ));
destination[2] = static_cast<uint8_t>(six_and_two_encoding_for_value( (source[1] << 2) | (source[2] >> 6) ));
destination[3] = static_cast<uint8_t>(six_and_two_encoding_for_value( source[2] ));
}*/
Storage::Disk::PCMSegment AppleGCR::six_and_two_sync(int length) {
return sync(length, 9);
}
@ -111,7 +111,7 @@ Storage::Disk::PCMSegment AppleGCR::header(uint8_t volume, uint8_t track, uint8_
return segment;
}
Storage::Disk::PCMSegment AppleGCR::five_and_three_data(uint8_t *source) {
Storage::Disk::PCMSegment AppleGCR::five_and_three_data(const uint8_t *source) {
Storage::Disk::PCMSegment segment;
segment.data.resize(410 + 7);
@ -119,25 +119,63 @@ Storage::Disk::PCMSegment AppleGCR::five_and_three_data(uint8_t *source) {
segment.data[1] = header_prologue[1];
segment.data[2] = header_prologue[2];
std::size_t source_pointer = 0;
std::size_t destination_pointer = 3;
while(source_pointer < 255) {
encode_five_and_three_block(&segment.data[destination_pointer], &source[source_pointer]);
source_pointer += 5;
destination_pointer += 8;
}
// std::size_t source_pointer = 0;
// std::size_t destination_pointer = 3;
// while(source_pointer < 255) {
// encode_five_and_three_block(&segment.data[destination_pointer], &source[source_pointer]);
//
// source_pointer += 5;
// destination_pointer += 8;
// }
return segment;
}
Storage::Disk::PCMSegment AppleGCR::six_and_two_data(uint8_t *source) {
Storage::Disk::PCMSegment AppleGCR::six_and_two_data(const uint8_t *source) {
Storage::Disk::PCMSegment segment;
segment.data.resize(342 + 7);
segment.data.resize(349);
// Add the prologue and epilogue.
segment.data[0] = header_prologue[0];
segment.data[1] = header_prologue[1];
segment.data[2] = header_prologue[2];
segment.data[346] = epilogue[0];
segment.data[347] = epilogue[1];
segment.data[348] = epilogue[2];
// Fill in byte values: the first 86 bytes contain shuffled
// and combined copies of the bottom two bits of the sector
// contents; the 256 bytes afterwards are the remaining
// six bits.
const uint8_t bit_shuffle[] = {0, 2, 1, 3};
for(std::size_t c = 0; c < 85; ++c) {
segment.data[3 + c] =
static_cast<uint8_t>(
bit_shuffle[source[c]&3] |
(bit_shuffle[source[c + 85]&3] << 2) |
(bit_shuffle[source[c + 170]&3] << 4)
);
}
segment.data[3 + 85] = bit_shuffle[source[255]&3];
for(std::size_t c = 0; c < 256; ++c) {
segment.data[3 + 85 + c] = source[c] >> 2;
}
// Exclusive OR each byte with the one before it.
segment.data[344] = segment.data[343];
std::size_t location = 343;
while(location > 3) {
segment.data[location] ^= segment.data[location-1];
--location;
}
// Map six-bit values up to full bytes.
for(std::size_t c = 0; c < 343; ++c) {
segment.data[c] = six_and_two_mapping[segment.data[c]];
}
return segment;
}

16
Storage/Disk/Encodings/AppleGCR.hpp
View File

@ -20,22 +20,22 @@ namespace AppleGCR {
/*!
@returns the eight-bit 13-sector GCR encoding for the low five bits of @c value.
*/
unsigned int five_and_three_encoding_for_value(int value);
// unsigned int five_and_three_encoding_for_value(int value);
/*!
@returns the eight-bit 16-sector GCR encoding for the low six bits of @c value.
*/
unsigned int six_and_two_encoding_for_value(int value);
// unsigned int six_and_two_encoding_for_value(int value);
/*!
A block is defined to be five source bytes, which encodes to eight GCR bytes.
*/
void encode_five_and_three_block(uint8_t *destination, uint8_t *source);
// void encode_five_and_three_block(uint8_t *destination, uint8_t *source);
/*!
A block is defined to be three source bytes, which encodes to four GCR bytes.
*/
void encode_six_and_two_block(uint8_t *destination, uint8_t *source);
// void encode_six_and_two_block(uint8_t *destination, uint8_t *source);
/*!
@returns the four bit nibble for the five-bit GCR @c quintet if a valid GCR value; INT_MAX otherwise.
@ -54,12 +54,16 @@ namespace AppleGCR {
/// Describes the epilogue that ends both data sections and headers.
const uint8_t epilogue[3] = {0xde, 0xaa, 0xeb};
/*!
Produces the Apple-standard '4 and 4' per-sector header. This is the same
for both the 13- and 16-sector formats, and is 112 bits long.
*/
Storage::Disk::PCMSegment header(uint8_t volume, uint8_t track, uint8_t sector);
Storage::Disk::PCMSegment six_and_two_data(uint8_t *source);
Storage::Disk::PCMSegment six_and_two_data(const uint8_t *source);
Storage::Disk::PCMSegment six_and_two_sync(int length);
Storage::Disk::PCMSegment five_and_three_data(uint8_t *source);
Storage::Disk::PCMSegment five_and_three_data(const uint8_t *source);
Storage::Disk::PCMSegment five_and_three_sync(int length);
}