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Fixed: the sector number also goes into sector bodies.

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Also the checksum is written in the other order, and the final byte of data isn't output.
This commit is contained in:
Thomas Harte
2019-06-18 10:34:10 -04:00
parent 756641e837
commit df56e6fe53
4 changed files with 24 additions and 16 deletions
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Storage/Disk/Encodings/AppleGCR/Encoder.cpp
+17 -9
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@@ -232,7 +232,7 @@ Storage::Disk::PCMSegment AppleGCR::Macintosh::header(uint8_t type, uint8_t trac
return Storage::Disk::PCMSegment(data);
}
Storage::Disk::PCMSegment AppleGCR::Macintosh::data(const uint8_t *source) {
Storage::Disk::PCMSegment AppleGCR::Macintosh::data(uint8_t sector, const uint8_t *source) {
std::vector<uint8_t> output(710);
int checksum[3] = {0, 0, 0};
@@ -241,6 +241,9 @@ Storage::Disk::PCMSegment AppleGCR::Macintosh::data(const uint8_t *source) {
output[1] = data_prologue[1];
output[2] = data_prologue[2];
// Add the sector number.
output[3] = six_and_two_mapping[sector & 0x3f];
// The Macintosh has a similar checksum-as-it-goes approach to encoding
// to the Apple II, but works entirely differently. Each three bytes of
// input are individually encoded to four GCR bytes, their output values
@@ -284,10 +287,10 @@ Storage::Disk::PCMSegment AppleGCR::Macintosh::data(const uint8_t *source) {
// Having mutated those three bytes according to the current checksum,
// and the checksum according to those bytes, run them through the
// GCR conversion table.
output[3 + c*4 + 1] = six_and_two_mapping[values[0] & 0x3f];
output[3 + c*4 + 2] = six_and_two_mapping[values[1] & 0x3f];
output[3 + c*4 + 3] = six_and_two_mapping[values[2] & 0x3f];
output[3 + c*4 + 0] = six_and_two_mapping[
output[4 + c*4 + 1] = six_and_two_mapping[values[0] & 0x3f];
output[4 + c*4 + 2] = six_and_two_mapping[values[1] & 0x3f];
output[4 + c*4 + 3] = six_and_two_mapping[values[2] & 0x3f];
output[4 + c*4 + 0] = six_and_two_mapping[
((values[0] >> 2) & 0x30) |
((values[1] >> 4) & 0x0c) |
((values[2] >> 6) & 0x03)
@@ -295,13 +298,18 @@ Storage::Disk::PCMSegment AppleGCR::Macintosh::data(const uint8_t *source) {
}
// Also write the checksum.
output[704] = six_and_two_mapping[checksum[0] & 0x3f];
//
// Caveat: the first byte written here will overwrite the final byte that
// was deposited in the loop above. That's deliberate. The final byte from
// the loop above doesn't contain any useful content, and isn't actually
// included on disk.
output[704] = six_and_two_mapping[checksum[2] & 0x3f];
output[705] = six_and_two_mapping[checksum[1] & 0x3f];
output[706] = six_and_two_mapping[checksum[2] & 0x3f];
output[706] = six_and_two_mapping[checksum[0] & 0x3f];
output[703] = six_and_two_mapping[
((checksum[0] >> 2) & 0x30) |
((checksum[2] >> 2) & 0x30) |
((checksum[1] >> 4) & 0x0c) |
((checksum[2] >> 6) & 0x03)
((checksum[0] >> 6) & 0x03)
];
// Write epilogue.