diskii/lib/disk/dsk.go

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// Copyright © 2016 Zellyn Hunter <zellyn@gmail.com>
// dsk.go contains logic for reading ".dsk" disk images.
package disk
import (
"fmt"
"io"
"io/ioutil"
)
// DSK represents a .dsk disk image.
type DSK struct {
data []byte // The actual data in the file
sectors byte // Number of sectors per track
physicalToStored []byte // Map of physical on-disk sector numbers to sectors in the disk image
bytesPerTrack int // Number of bytes per track
tracks byte // Number of tracks
}
var _ SectorDisk = (*DSK)(nil)
// LoadDSK loads a .dsk image from a file.
func LoadDSK(filename string) (DSK, error) {
bb, err := ioutil.ReadFile(filename)
if err != nil {
return DSK{}, err
}
// TODO(zellyn): handle 13-sector disks.
if len(bb) != DOS33DiskBytes {
return DSK{}, fmt.Errorf("expected file %q to contain %d bytes, but got %d", filename, DOS33DiskBytes, len(bb))
}
return DSK{
data: bb,
sectors: 16,
physicalToStored: Dos33PhysicalToLogicalSectorMap,
bytesPerTrack: 16 * 256,
tracks: DOS33Tracks,
}, nil
}
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// Empty creates a .dsk image that is all zeros.
func Empty() DSK {
return DSK{
data: make([]byte, DOS33DiskBytes),
sectors: 16,
physicalToStored: Dos33PhysicalToLogicalSectorMap,
bytesPerTrack: 16 * 256,
tracks: DOS33Tracks,
}
}
// ReadPhysicalSector reads a single physical sector from the disk. It
// always returns 256 byes.
func (d DSK) ReadPhysicalSector(track byte, sector byte) ([]byte, error) {
if track >= d.tracks {
return nil, fmt.Errorf("ReadPhysicalSector expected track between 0 and %d; got %d", d.tracks-1, track)
}
if sector >= d.sectors {
return nil, fmt.Errorf("ReadPhysicalSector expected sector between 0 and %d; got %d", d.sectors-1, sector)
}
storedSector := d.physicalToStored[int(sector)]
start := int(track)*d.bytesPerTrack + 256*int(storedSector)
buf := make([]byte, 256)
copy(buf, d.data[start:start+256])
return buf, nil
}
// WritePhysicalSector writes a single physical sector to a disk. It
// expects exactly 256 bytes.
func (d DSK) WritePhysicalSector(track byte, sector byte, data []byte) error {
if track >= d.tracks {
return fmt.Errorf("WritePhysicalSector expected track between 0 and %d; got %d", d.tracks-1, track)
}
if sector >= d.sectors {
return fmt.Errorf("WritePhysicalSector expected sector between 0 and %d; got %d", d.sectors-1, sector)
}
if len(data) != 256 {
return fmt.Errorf("WritePhysicalSector expects data of length 256; got %d", len(data))
}
storedSector := d.physicalToStored[int(sector)]
start := int(track)*d.bytesPerTrack + 256*int(storedSector)
copy(d.data[start:start+256], data)
return nil
}
// Sectors returns the number of sectors on the DSK image.
func (d DSK) Sectors() byte {
return d.sectors
}
// Tracks returns the number of tracks on the DSK image.
func (d DSK) Tracks() byte {
return d.tracks
}
// Write writes the disk contents to the given file.
func (d DSK) Write(w io.Writer) (n int, err error) {
return w.Write(d.data)
}