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Removes requirement for correct sector epilogues.

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It's now a length test that at present accepts 6-and-2 sectors only.
This commit is contained in:
Thomas Harte 2018-05-12 23:03:08 -04:00
parent 49592ebaf3
commit 3fdefb94e4
1 changed files with 41 additions and 48 deletions
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89
Storage/Disk/Encodings/AppleGCR/SegmentParser.cpp
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@ -85,18 +85,15 @@ std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment
}
} else {
if(new_sector) {
// If this is an epilogue, make sense of this whole sector;
// otherwise just keep the byte for later.
if(scanner[1] == epilogue[0] && scanner[2] == epilogue[1]) {
new_sector->data.push_back(value);
// If this is potentially a complete sector, check it out.
if(new_sector->data.size() == 343) {
// TODO: allow for 13-sector form.
std::unique_ptr<Sector> sector = std::move(new_sector);
new_sector.reset();
pointer = scanning_sentinel;
// Check for an expected size; the first byte of the epilogue has been stored, so
// these numbers are one bigger than usual.
if(sector->data.size() != 412 && sector->data.size() != 344) continue;
sector->data.resize(sector->data.size() - 1);
// Check for apparent four and four encoding.
uint_fast8_t header_mask = 0xff;
for(auto c : header) header_mask &= c;
@ -111,54 +108,50 @@ std::map<std::size_t, Sector> Storage::Encodings::AppleGCR::sectors_from_segment
uint_fast8_t checksum = ((header[6] << 1) | 1) & header[7];
if(checksum != (sector->address.volume^sector->address.track^sector->address.sector)) continue;
if(sector->data.size() == 343) {
// Unmap the sector contents as 6 and 2 data.
bool out_of_bounds = false;
for(auto &c : sector->data) {
if(c < 0x96 || six_and_two_unmapping[c - 0x96] == 0xff) {
out_of_bounds = true;
break;
}
c = six_and_two_unmapping[c - 0x96];
// Unmap the sector contents as 6 and 2 data.
bool out_of_bounds = false;
for(auto &c : sector->data) {
if(c < 0x96 || six_and_two_unmapping[c - 0x96] == 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);
// Undo the 6 and 2 mapping.
const uint8_t bit_reverse[] = {0, 2, 1, 3};
#define unmap(byte, nibble, shift) \
sector->data[86 + byte] = static_cast<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
c = six_and_two_unmapping[c - 0x96];
}
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);
// Undo the 6 and 2 mapping.
const uint8_t bit_reverse[] = {0, 2, 1, 3};
#define unmap(byte, nibble, shift) \
sector->data[86 + byte] = static_cast<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.
sector->data.erase(sector->data.begin(), sector->data.end() - 256);
// Add this sector to the map.
result.insert(std::make_pair(sector_location, std::move(*sector)));
} else {
new_sector->data.push_back(value);
}
} else {
// Just capture the header in place; it'll be decoded