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Correct FAT parser.

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This commit is contained in:
Thomas Harte 2021-07-02 19:28:13 -04:00
parent fe07a0b1d8
commit a5b7d819a7
2 changed files with 24 additions and 31 deletions
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49
Storage/Disk/Parsers/FAT.cpp
View File

@ -15,18 +15,19 @@
using namespace Storage::Disk;
FAT::Volume::CHS FAT::Volume::chs_for_sector(int sector) const {
const auto sectors_per_head = total_sectors / head_count;
const auto track = sector / sectors_per_track;
// Guess here: there's no head interleaving. Let's see.
// Sides are interleaved.
return CHS{
sector / sectors_per_head,
(sector % sectors_per_head) / sectors_per_track,
track / head_count,
track % head_count,
1 + (sector % sectors_per_track)
};
}
int FAT::Volume::sector_for_cluster(int cluster) const {
return (cluster * sectors_per_cluster) + first_data_sector;
int FAT::Volume::sector_for_cluster(uint16_t cluster) const {
// The first cluster in the data area is numbered as 2.
return ((cluster - 2) * sectors_per_cluster) + first_data_sector;
}
namespace {
@ -34,6 +35,7 @@ namespace {
FAT::Directory directory_from(const std::vector<uint8_t> &contents) {
FAT::Directory result;
// Worst case: parse until the amount of data supplied is fully consumed.
for(size_t base = 0; base < contents.size(); base += 32) {
// An entry starting with byte 0 indicates end-of-directory.
if(!contents[base]) {
@ -80,6 +82,7 @@ std::optional<FAT::Volume> FAT::GetVolume(const std::shared_ptr<Storage::Disk::D
FAT::Volume volume;
volume.bytes_per_sector = uint16_t(data[11] | (data[12] << 8));
volume.sectors_per_cluster = data[13];
volume.reserved_sectors = uint16_t(data[14] | (data[15] << 8));
volume.fat_copies = data[16];
const uint16_t root_directory_entries = uint16_t(data[17] | (data[18] << 8));
volume.total_sectors = uint16_t(data[19] | (data[20] << 8));
@ -109,14 +112,14 @@ std::optional<FAT::Volume> FAT::GetVolume(const std::shared_ptr<Storage::Disk::D
// TODO: stop assuming FAT12 here.
for(size_t c = 0; c < source_fat.size(); c += 3) {
const uint32_t double_cluster = uint32_t(source_fat[c] + (source_fat[c + 1] << 8) + (source_fat[c + 2] << 16));
volume.fat.push_back(double_cluster & 0xfff);
volume.fat.push_back(double_cluster >> 12);
volume.fat.push_back(uint16_t(double_cluster & 0xfff));
volume.fat.push_back(uint16_t(double_cluster >> 12));
}
// Grab the root directory.
std::vector<uint8_t> root_directory;
for(size_t c = 0; c < root_directory_sectors; c++) {
const auto sector_number = int(1 + c + volume.sectors_per_fat*volume.fat_copies);
const auto sector_number = int(volume.reserved_sectors + c + volume.sectors_per_fat*volume.fat_copies);
const auto address = volume.chs_for_sector(sector_number);
Storage::Encodings::MFM::Sector *const sector =
@ -128,19 +131,6 @@ std::optional<FAT::Volume> FAT::GetVolume(const std::shared_ptr<Storage::Disk::D
}
volume.root_directory = directory_from(root_directory);
// TEST!
// TODO: REMOVE.
for(const auto &file: volume.root_directory) {
if(!(file.attributes & File::Attribute::Directory)) {
continue;
}
const auto sub = GetDirectory(disk, volume, file);
if(!sub) {
continue;
}
std::cout << (*sub).size();
}
return volume;
}
@ -148,14 +138,15 @@ std::optional<std::vector<uint8_t>> FAT::GetFile(const std::shared_ptr<Storage::
Storage::Encodings::MFM::Parser parser(true, disk);
std::vector<uint8_t> contents;
// In FAT cluster numbers describe a linked list via the FAT table, with values above $FF0 being reserved
// (relevantly: FF7 means bad cluster; FF8–FFF mean end-of-file).
uint16_t cluster = file.starting_cluster;
while(contents.size() < file.size) {
int sector = volume.sector_for_cluster(cluster);
++cluster;
do {
const int sector = volume.sector_for_cluster(cluster);
for(int c = 0; c < volume.sectors_per_cluster; c++) {
const auto address = volume.chs_for_sector(sector);
++sector;
const auto address = volume.chs_for_sector(sector + c);
Storage::Encodings::MFM::Sector *const sector_contents =
parser.get_sector(address.head, address.cylinder, uint8_t(address.sector));
@ -164,7 +155,9 @@ std::optional<std::vector<uint8_t>> FAT::GetFile(const std::shared_ptr<Storage::
}
std::copy(sector_contents->samples[0].begin(), sector_contents->samples[0].end(), std::back_inserter(contents));
}
}
cluster = volume.fat[cluster];
} while(cluster < 0xff0);
return contents;
}

6
Storage/Disk/Parsers/FAT.hpp
View File

@ -44,7 +44,7 @@ using Directory = std::vector<File>;
struct Volume {
uint16_t bytes_per_sector = 0;
uint8_t sectors_per_cluster = 0;
uint8_t reserved_sectors = 0;
uint16_t reserved_sectors = 0;
uint8_t fat_copies = 0;
uint16_t total_sectors = 0;
uint16_t sectors_per_fat = 0;
@ -54,7 +54,7 @@ struct Volume {
bool correct_signature = false;
int first_data_sector = 0;
std::vector<uint32_t> fat;
std::vector<uint16_t> fat;
Directory root_directory;
struct CHS {
@ -65,7 +65,7 @@ struct Volume {
/// @returns a direct sector -> CHS address translation.
CHS chs_for_sector(int sector) const;
/// @returns the CHS address for the numbered cluster within the data area.
int sector_for_cluster(int cluster) const;
int sector_for_cluster(uint16_t cluster) const;
};
std::optional<Volume> GetVolume(const std::shared_ptr<Storage::Disk::Disk> &disk);