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Compacts gaps when necessary to fit more sectors.

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This commit is contained in:
Thomas Harte 2019-12-19 19:22:48 -05:00
parent d802e8aee3
commit 4605b1b264
1 changed files with 61 additions and 9 deletions
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70
Storage/Disk/Encodings/MFM/Encoder.cpp
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@ -16,6 +16,11 @@
using namespace Storage::Encodings::MFM;
enum class SurfaceItem {
Mark,
Data
};
class MFMEncoder: public Encoder {
public:
MFMEncoder(std::vector<bool> &target) : Encoder(target) {}
@ -59,6 +64,14 @@ class MFMEncoder: public Encoder {
add_byte(DeletedDataAddressByte);
}
size_t item_size(SurfaceItem item) {
switch(item) {
case SurfaceItem::Mark: return 8; // Three syncs plus the mark type.
case SurfaceItem::Data: return 2; // Just a single encoded byte.
default: assert(false);
}
}
private:
uint16_t last_output_;
void output_short(uint16_t value) {
@ -116,6 +129,11 @@ class FMEncoder: public Encoder {
crc_generator_.add(DeletedDataAddressByte);
output_short(FMDeletedDataAddressMark);
}
size_t item_size(SurfaceItem item) {
// Marks are just slightly-invalid bytes, so everything is the same length.
return 2;
}
};
template<class T> std::shared_ptr<Storage::Disk::Track>
@ -131,18 +149,53 @@ template<class T> std::shared_ptr<Storage::Disk::Track>
segment.data.reserve(expected_track_bytes * 8);
T shifter(segment.data);
// output the index mark
// Make a pre-estimate of output size, in case any of the idealised gaps
// provided need to be shortened.
const size_t data_size = shifter.item_size(SurfaceItem::Data);
const size_t mark_size = shifter.item_size(SurfaceItem::Mark);
const size_t max_size = (expected_track_bytes + (expected_track_bytes / 10)) * 8;
size_t total_sector_bytes = 0;
for(const auto sector : sectors) {
total_sector_bytes += size_t(128 << sector->size) + 2;
}
while(true) {
const size_t size =
mark_size +
post_index_address_mark_bytes * data_size +
total_sector_bytes * data_size +
sectors.size() * (
(pre_address_mark_bytes + 6 + post_address_mark_bytes + pre_data_mark_bytes + post_data_bytes) * data_size + 2 * mark_size
);
// If this track already fits, do nothing.
if(size*8 < max_size) break;
// If all gaps are already zero, do nothing.
if(!post_index_address_mark_bytes && !pre_address_mark_bytes && !post_address_mark_bytes && !pre_data_mark_bytes && !post_data_bytes)
break;
// Very simple solution: try halving all gaps.
post_index_address_mark_bytes >>= 1;
pre_address_mark_bytes >>= 1;
post_address_mark_bytes >>= 1;
pre_data_mark_bytes >>= 1;
post_data_bytes >>= 1;
}
// Output the index mark.
shifter.add_index_address_mark();
// add the post-index mark
// Add the post-index mark.
for(std::size_t c = 0; c < post_index_address_mark_bytes; c++) shifter.add_byte(post_index_address_mark_value);
// add sectors
// Add sectors.
for(const Sector *sector : sectors) {
// gap
// Gap.
for(std::size_t c = 0; c < pre_address_mark_bytes; c++) shifter.add_byte(0x00);
// sector header
// Sector header.
shifter.add_ID_address_mark();
shifter.add_byte(sector->address.track);
shifter.add_byte(sector->address.side);
@ -150,11 +203,11 @@ template<class T> std::shared_ptr<Storage::Disk::Track>
shifter.add_byte(sector->size);
shifter.add_crc(sector->has_header_crc_error);
// gap
// Gap.
for(std::size_t c = 0; c < post_address_mark_bytes; c++) shifter.add_byte(post_address_mark_value);
for(std::size_t c = 0; c < pre_data_mark_bytes; c++) shifter.add_byte(0x00);
// data, if attached
// Data, if attached.
// TODO: allow for weak/fuzzy data.
if(!sector->samples.empty()) {
if(sector->is_deleted)
@ -173,14 +226,13 @@ template<class T> std::shared_ptr<Storage::Disk::Track>
shifter.add_crc(sector->has_data_crc_error);
}
// gap
// Gap.
for(std::size_t c = 0; c < post_data_bytes; c++) shifter.add_byte(post_data_value);
}
while(segment.data.size() < expected_track_bytes*8) shifter.add_byte(0x00);
// Allow the amount of data written to be up to 10% more than the expected size. Which is generous.
const std::size_t max_size = (expected_track_bytes + (expected_track_bytes / 10)) * 8;
if(segment.data.size() > max_size) segment.data.resize(max_size);
return std::shared_ptr<Storage::Disk::Track>(new Storage::Disk::PCMTrack(std::move(segment)));