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97 lines
2.6 KiB
C++
97 lines
2.6 KiB
C++
//
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// MSA.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 03/10/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#include "MSA.hpp"
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#include "Utility/ImplicitSectors.hpp"
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#include <cassert>
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using namespace Storage::Disk;
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MSA::MSA(const std::string &file_name) :
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file_(file_name) {
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const auto signature = file_.get16be();
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if(signature != 0x0e0f) throw Error::InvalidFormat;
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sectors_per_track_ = file_.get16be();
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sides_ = 1 + file_.get16be();
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starting_track_ = file_.get16be();
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ending_track_ = file_.get16be();
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// Create the uncompressed track list.
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while(true) {
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const auto data_length = file_.get16be();
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if(file_.eof()) break;
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if(data_length == sectors_per_track_ * 512) {
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// This is an uncompressed track.
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uncompressed_tracks_.push_back(file_.read(data_length));
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} else {
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#ifndef NDEBUG
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const auto start_of_track = file_.tell();
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#endif
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// This is an RLE-compressed track.
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std::vector<uint8_t> track;
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track.reserve(sectors_per_track_ * 512);
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uint16_t pointer = 0;
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while(pointer < data_length) {
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const auto byte = file_.get8();
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// Compression scheme: if the byte E5 is encountered, an RLE run follows.
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// An RLE run is encoded as the byte to repeat plus a 16-bit repeat count.
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if(byte != 0xe5) {
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track.push_back(byte);
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++pointer;
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continue;
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}
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pointer += 4;
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if(pointer > data_length) break;
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const auto value = file_.get8();
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auto count = file_.get16be();
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while(count--) {
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track.push_back(value);
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}
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}
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#ifndef NDEBUG
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assert(file_.tell() - start_of_track == pointer);
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#endif
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if(pointer != data_length || track.size() != sectors_per_track_ * 512)
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throw Error::InvalidFormat;
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uncompressed_tracks_.push_back(std::move(track));
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}
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}
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if(uncompressed_tracks_.size() != size_t((ending_track_ - starting_track_ + 1)*sides_))
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throw Error::InvalidFormat;
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}
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std::shared_ptr<::Storage::Disk::Track> MSA::get_track_at_position(::Storage::Disk::Track::Address address) {
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if(address.head >= sides_) return nullptr;
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const auto position = address.position.as_int();
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if(position < starting_track_) return nullptr;
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if(position > ending_track_) return nullptr;
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const auto &track = uncompressed_tracks_[size_t(position - starting_track_) * size_t(sides_) + size_t(address.head)];
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assert(!track.empty());
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return track_for_sectors(track.data(), sectors_per_track_, uint8_t(position), uint8_t(address.head), 1, 2, Storage::Encodings::MFM::Density::Double);
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}
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HeadPosition MSA::get_maximum_head_position() {
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return HeadPosition(ending_track_ + 1);
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}
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int MSA::get_head_count() {
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return sides_;
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}
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