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181 lines
4.9 KiB
C++
181 lines
4.9 KiB
C++
//
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// AppleGCR.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 21/04/2018.
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// Copyright 2018 Thomas Harte. All rights reserved.
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//
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#include "Encoder.hpp"
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namespace {
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const uint8_t five_and_three_mapping[] = {
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0xab, 0xad, 0xae, 0xaf, 0xb5, 0xb6, 0xb7, 0xba,
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0xbb, 0xbd, 0xbe, 0xbf, 0xd6, 0xd7, 0xda, 0xdb,
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0xdd, 0xde, 0xdf, 0xea, 0xeb, 0xed, 0xee, 0xef,
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0xf5, 0xf6, 0xf7, 0xfa, 0xfb, 0xfd, 0xfe, 0xff
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};
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const uint8_t six_and_two_mapping[] = {
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0x96, 0x97, 0x9a, 0x9b, 0x9d, 0x9e, 0x9f, 0xa6,
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0xa7, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb2, 0xb3,
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0xb4, 0xb5, 0xb6, 0xb7, 0xb9, 0xba, 0xbb, 0xbc,
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0xbd, 0xbe, 0xbf, 0xcb, 0xcd, 0xce, 0xcf, 0xd3,
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0xd6, 0xd7, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde,
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0xdf, 0xe5, 0xe6, 0xe7, 0xe9, 0xea, 0xeb, 0xec,
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0xed, 0xee, 0xef, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6,
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0xf7, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
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};
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/*!
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Produces a PCM segment containing @c length sync bytes, each aligned to the beginning of
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a @c bit_size -sized window.
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*/
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Storage::Disk::PCMSegment sync(int length, int bit_size) {
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Storage::Disk::PCMSegment segment;
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// Allocate sufficient storage.
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segment.data.resize(static_cast<size_t>(((length * bit_size) + 7) >> 3), 0);
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while(length--) {
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segment.data[segment.number_of_bits >> 3] |= 0xff >> (segment.number_of_bits & 7);
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if(segment.number_of_bits & 7) {
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segment.data[1 + (segment.number_of_bits >> 3)] |= 0xff << (8 - (segment.number_of_bits & 7));
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}
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segment.number_of_bits += static_cast<unsigned int>(bit_size);
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}
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return segment;
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}
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}
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using namespace Storage::Encodings;
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Storage::Disk::PCMSegment AppleGCR::six_and_two_sync(int length) {
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return sync(length, 10);
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}
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Storage::Disk::PCMSegment AppleGCR::five_and_three_sync(int length) {
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return sync(length, 9);
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}
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Storage::Disk::PCMSegment AppleGCR::header(uint8_t volume, uint8_t track, uint8_t sector) {
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const uint8_t checksum = volume ^ track ^ sector;
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// Apple headers are encoded using an FM-esque scheme rather than 6 and 2, or 5 and 3.
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Storage::Disk::PCMSegment segment;
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segment.data.resize(14);
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segment.number_of_bits = 14*8;
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segment.data[0] = header_prologue[0];
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segment.data[1] = header_prologue[1];
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segment.data[2] = header_prologue[2];
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#define WriteFM(index, value) \
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segment.data[index+0] = static_cast<uint8_t>(((value) >> 1) | 0xaa); \
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segment.data[index+1] = static_cast<uint8_t>((value) | 0xaa); \
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WriteFM(3, volume);
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WriteFM(5, track);
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WriteFM(7, sector);
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WriteFM(9, checksum);
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#undef WriteFM
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segment.data[11] = epilogue[0];
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segment.data[12] = epilogue[1];
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segment.data[13] = epilogue[2];
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return segment;
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}
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Storage::Disk::PCMSegment AppleGCR::five_and_three_data(const uint8_t *source) {
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Storage::Disk::PCMSegment segment;
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segment.data.resize(410 + 7);
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segment.data[0] = data_prologue[0];
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segment.data[1] = data_prologue[1];
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segment.data[2] = data_prologue[2];
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segment.data[414] = epilogue[0];
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segment.data[411] = epilogue[1];
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segment.data[416] = epilogue[2];
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// std::size_t source_pointer = 0;
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// std::size_t destination_pointer = 3;
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// while(source_pointer < 255) {
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// encode_five_and_three_block(&segment.data[destination_pointer], &source[source_pointer]);
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//
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// source_pointer += 5;
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// destination_pointer += 8;
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// }
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// Map five-bit values up to full bytes.
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for(std::size_t c = 0; c < 410; ++c) {
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segment.data[3 + c] = five_and_three_mapping[segment.data[3 + c]];
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}
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return segment;
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}
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Storage::Disk::PCMSegment AppleGCR::six_and_two_data(const uint8_t *source) {
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Storage::Disk::PCMSegment segment;
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segment.data.resize(349);
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segment.number_of_bits = static_cast<unsigned int>(segment.data.size() * 8);
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// Add the prologue and epilogue.
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segment.data[0] = data_prologue[0];
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segment.data[1] = data_prologue[1];
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segment.data[2] = data_prologue[2];
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segment.data[346] = epilogue[0];
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segment.data[347] = epilogue[1];
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segment.data[348] = epilogue[2];
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// Fill in byte values: the first 86 bytes contain shuffled
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// and combined copies of the bottom two bits of the sector
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// contents; the 256 bytes afterwards are the remaining
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// six bits.
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const uint8_t bit_reverse[] = {0, 2, 1, 3};
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for(std::size_t c = 0; c < 84; ++c) {
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segment.data[3 + c] =
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static_cast<uint8_t>(
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bit_reverse[source[c]&3] |
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(bit_reverse[source[c + 86]&3] << 2) |
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(bit_reverse[source[c + 172]&3] << 4)
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);
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}
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segment.data[87] =
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static_cast<uint8_t>(
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(bit_reverse[source[84]&3] << 0) |
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(bit_reverse[source[170]&3] << 2)
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);
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segment.data[88] =
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static_cast<uint8_t>(
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(bit_reverse[source[85]&3] << 0) |
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(bit_reverse[source[171]&3] << 2)
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);
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for(std::size_t c = 0; c < 256; ++c) {
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segment.data[3 + 86 + c] = source[c] >> 2;
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}
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// Exclusive OR each byte with the one before it.
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segment.data[345] = segment.data[344];
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std::size_t location = 344;
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while(location > 3) {
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segment.data[location] ^= segment.data[location-1];
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--location;
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}
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// Map six-bit values up to full bytes.
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for(std::size_t c = 0; c < 343; ++c) {
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segment.data[3 + c] = six_and_two_mapping[segment.data[3 + c]];
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}
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return segment;
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}
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