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Moves block byte writes into Storage::Encodings::MFM::Encoder.

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This commit is contained in:
Thomas Harte 2021-10-10 16:06:51 -07:00
parent 846b505d27
commit addf9f9af4
2 changed files with 25 additions and 11 deletions
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25
Storage/Disk/DiskImage/Formats/AmigaADF.cpp
View File

@ -18,6 +18,11 @@ using namespace Storage::Disk;
namespace {
/// Builds a buffer containing the bytes between @c begin and @c end split up so that the nibbles in the first half of the buffer
/// consist of the odd bits of the source bytes — b1, b3, b5 and b7 — ordered so that most-significant nibbles come before
/// least-significant ones, and the second half of the buffer contains the even bits.
///
/// Nibbles are written to @c first; it is assumed that an even number of source bytes have been supplied.
template <typename IteratorT, class OutputIt> void encode_block(IteratorT begin, IteratorT end, OutputIt first) {
// Parse 1: combine odd bits.
auto cursor = begin;
@ -62,13 +67,9 @@ template <typename IteratorT, class OutputIt> void encode_block(IteratorT begin,
}
}
template <typename IteratorT> void write(IteratorT begin, IteratorT end, std::unique_ptr<Storage::Encodings::MFM::Encoder> &encoder) {
while(begin != end) {
encoder->add_byte(*begin);
++begin;
}
}
/// Construsts the Amiga-style checksum of the bytes between @c begin and @c end, which is a 32-bit exclusive OR of the source data
/// with each byte converted into a 16-bit word by inserting a 0 bit between every data bit, and then combined into 32-bit words in
/// big endian order.
template <typename IteratorT> auto checksum(IteratorT begin, IteratorT end) {
uint16_t checksum[2]{};
int offset = 0;
@ -99,6 +100,8 @@ template <typename IteratorT> auto checksum(IteratorT begin, IteratorT end) {
};
}
/// Obtains the Amiga-style checksum of the data between @c begin and @c end, then odd-even encodes it and writes
/// it out to @c encoder.
template <typename IteratorT> void write_checksum(IteratorT begin, IteratorT end, std::unique_ptr<Storage::Encodings::MFM::Encoder> &encoder) {
// Believe it or not, this appears to be the actual checksum algorithm on the Amiga:
//
@ -110,7 +113,7 @@ template <typename IteratorT> void write_checksum(IteratorT begin, IteratorT end
std::decay_t<decltype(raw_checksum)> encoded_checksum{};
encode_block(raw_checksum.begin(), raw_checksum.end(), encoded_checksum.begin());
write(encoded_checksum.begin(), encoded_checksum.end(), encoder);
encoder->add_bytes(encoded_checksum.begin(), encoded_checksum.end());
}
}
@ -164,11 +167,11 @@ std::shared_ptr<Track> AmigaADF::get_track_at_position(Track::Address address) {
};
std::array<uint8_t, 4> encoded_header;
encode_block(std::begin(header), std::end(header), std::begin(encoded_header));
write(std::begin(encoded_header), std::end(encoded_header), encoder);
encoder->add_bytes(std::begin(encoded_header), std::end(encoded_header));
// Write the sector label.
const std::array<uint8_t, 16> os_recovery{};
write(os_recovery.begin(), os_recovery.end(), encoder);
encoder->add_bytes(os_recovery.begin(), os_recovery.end());
// Encode the data.
std::array<uint8_t, 512> encoded_data;
@ -179,7 +182,7 @@ std::shared_ptr<Track> AmigaADF::get_track_at_position(Track::Address address) {
write_checksum(std::begin(encoded_data), std::end(encoded_data), encoder);
// Write data.
write(std::begin(encoded_data), std::end(encoded_data), encoder);
encoder->add_bytes(std::begin(encoded_data), std::end(encoded_data));
}
return std::make_shared<Storage::Disk::PCMTrack>(std::move(encoded_segment));

11
Storage/Disk/Encodings/MFM/Encoder.hpp
View File

@ -55,6 +55,17 @@ class Encoder {
virtual void add_deleted_data_address_mark() = 0;
virtual void output_short(uint16_t value, uint16_t fuzzy_mask = 0);
template <typename IteratorT> void add_bytes(IteratorT begin, IteratorT end) {
while(begin != end) {
add_byte(*begin);
++begin;
}
}
template <typename ContainerT> void add_bytes(const ContainerT &container) {
write(std::begin(container), std::end(container));
}
/// Outputs the CRC for all data since the last address mask; if @c incorrectly is @c true then outputs an incorrect CRC.
void add_crc(bool incorrectly);