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180 lines
6.4 KiB
C++
180 lines
6.4 KiB
C++
//
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// FAT.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 02/07/2021.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#include "FAT.hpp"
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#include "../Encodings/MFM/Parser.hpp"
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#include <iostream>
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using namespace Storage::Disk;
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FAT::Volume::CHS FAT::Volume::chs_for_sector(int sector) const {
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const auto track = sector / sectors_per_track;
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// Sides are interleaved.
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return CHS{
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track / head_count,
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track % head_count,
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1 + (sector % sectors_per_track)
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};
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}
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int FAT::Volume::sector_for_cluster(uint16_t cluster) const {
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// The first cluster in the data area is numbered as 2.
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return ((cluster - 2) * sectors_per_cluster) + first_data_sector;
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}
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namespace {
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template <typename CharT> std::string trim(CharT start, CharT end) {
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std::string result(start, end);
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result.erase(std::find_if(result.rbegin(), result.rend(), [](unsigned char ch) {
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return !std::isspace(ch);
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}).base(), result.end());
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return result;
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}
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FAT::Directory directory_from(const std::vector<uint8_t> &contents) {
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FAT::Directory result;
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// Worst case: parse until the amount of data supplied is fully consumed.
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for(size_t base = 0; base < contents.size(); base += 32) {
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// An entry starting with byte 0 indicates end-of-directory.
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if(!contents[base]) {
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break;
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}
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// An entry starting in 0xe5 is merely deleted.
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if(contents[base] == 0xe5) {
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continue;
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}
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// Otherwise create and populate a new entry.
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result.emplace_back();
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result.back().name = trim(&contents[base], &contents[base+8]);
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result.back().extension = trim(&contents[base+8], &contents[base+11]);
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result.back().attributes = contents[base + 11];
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result.back().time = uint16_t(contents[base+22] | (contents[base+23] << 8));
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result.back().date = uint16_t(contents[base+24] | (contents[base+25] << 8));
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result.back().starting_cluster = uint16_t(contents[base+26] | (contents[base+27] << 8));
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result.back().size = uint32_t(
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contents[base+28] |
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(contents[base+29] << 8) |
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(contents[base+30] << 16) |
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(contents[base+31] << 24)
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);
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}
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return result;
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}
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}
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std::optional<FAT::Volume> FAT::GetVolume(const std::shared_ptr<Storage::Disk::Disk> &disk) {
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Storage::Encodings::MFM::Parser parser(Storage::Encodings::MFM::Density::Double, disk);
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// Grab the boot sector; that'll be enough to establish the volume.
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const Storage::Encodings::MFM::Sector *const boot_sector = parser.sector(0, 0, 1);
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if(!boot_sector || boot_sector->samples.empty() || boot_sector->samples[0].size() < 512) {
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return std::nullopt;
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}
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// Obtain volume details.
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const auto &data = boot_sector->samples[0];
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FAT::Volume volume;
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volume.bytes_per_sector = uint16_t(data[11] | (data[12] << 8));
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volume.sectors_per_cluster = data[13];
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volume.reserved_sectors = uint16_t(data[14] | (data[15] << 8));
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volume.fat_copies = data[16];
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const uint16_t root_directory_entries = uint16_t(data[17] | (data[18] << 8));
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volume.total_sectors = uint16_t(data[19] | (data[20] << 8));
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volume.sectors_per_fat = uint16_t(data[22] | (data[23] << 8));
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volume.sectors_per_track = uint16_t(data[24] | (data[25] << 8));
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volume.head_count = uint16_t(data[26] | (data[27] << 8));
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volume.correct_signature = data[510] == 0x55 && data[511] == 0xaa;
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const size_t root_directory_sectors = (root_directory_entries*32 + volume.bytes_per_sector - 1) / volume.bytes_per_sector;
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volume.first_data_sector = int(volume.reserved_sectors + volume.sectors_per_fat*volume.fat_copies + root_directory_sectors);
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// Grab the FAT.
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std::vector<uint8_t> source_fat;
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for(int c = 0; c < volume.sectors_per_fat; c++) {
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const int sector_number = volume.reserved_sectors + c;
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const auto address = volume.chs_for_sector(sector_number);
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const Storage::Encodings::MFM::Sector *const fat_sector =
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parser.sector(address.head, address.cylinder, uint8_t(address.sector));
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if(!fat_sector || fat_sector->samples.empty() || fat_sector->samples[0].size() != volume.bytes_per_sector) {
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return std::nullopt;
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}
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std::copy(fat_sector->samples[0].begin(), fat_sector->samples[0].end(), std::back_inserter(source_fat));
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}
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// Decode the FAT.
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// TODO: stop assuming FAT12 here.
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for(size_t c = 0; c < source_fat.size(); c += 3) {
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const uint32_t double_cluster = uint32_t(source_fat[c] + (source_fat[c + 1] << 8) + (source_fat[c + 2] << 16));
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volume.fat.push_back(uint16_t(double_cluster & 0xfff));
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volume.fat.push_back(uint16_t(double_cluster >> 12));
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}
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// Grab the root directory.
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std::vector<uint8_t> root_directory;
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for(size_t c = 0; c < root_directory_sectors; c++) {
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const auto sector_number = int(volume.reserved_sectors + c + volume.sectors_per_fat*volume.fat_copies);
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const auto address = volume.chs_for_sector(sector_number);
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const Storage::Encodings::MFM::Sector *const sector =
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parser.sector(address.head, address.cylinder, uint8_t(address.sector));
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if(!sector || sector->samples.empty() || sector->samples[0].size() != volume.bytes_per_sector) {
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return std::nullopt;
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}
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std::copy(sector->samples[0].begin(), sector->samples[0].end(), std::back_inserter(root_directory));
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}
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volume.root_directory = directory_from(root_directory);
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return volume;
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}
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std::optional<std::vector<uint8_t>> FAT::GetFile(const std::shared_ptr<Storage::Disk::Disk> &disk, const Volume &volume, const File &file) {
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Storage::Encodings::MFM::Parser parser(Storage::Encodings::MFM::Density::Double, disk);
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std::vector<uint8_t> contents;
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// In FAT cluster numbers describe a linked list via the FAT table, with values above $FF0 being reserved
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// (relevantly: FF7 means bad cluster; FF8–FFF mean end-of-file).
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uint16_t cluster = file.starting_cluster;
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do {
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const int sector = volume.sector_for_cluster(cluster);
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for(int c = 0; c < volume.sectors_per_cluster; c++) {
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const auto address = volume.chs_for_sector(sector + c);
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const Storage::Encodings::MFM::Sector *const sector_contents =
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parser.sector(address.head, address.cylinder, uint8_t(address.sector));
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if(!sector_contents || sector_contents->samples.empty() || sector_contents->samples[0].size() != volume.bytes_per_sector) {
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return std::nullopt;
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}
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std::copy(sector_contents->samples[0].begin(), sector_contents->samples[0].end(), std::back_inserter(contents));
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}
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cluster = volume.fat[cluster];
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} while(cluster < 0xff0);
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return contents;
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}
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std::optional<FAT::Directory> FAT::GetDirectory(const std::shared_ptr<Storage::Disk::Disk> &disk, const Volume &volume, const File &file) {
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const auto contents = GetFile(disk, volume, file);
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if(!contents) {
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return std::nullopt;
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}
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return directory_from(*contents);
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}
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