Class ParentMap

Namespace: CHDSharp.Encoder

Assembly: CHDSharpLib.dll

Builds the parent-hunk hash map used to create differential (delta) CHDs. The parent CHD is decompressed once, and every unit-aligned window of its data (one hunk's worth of bytes starting at each unit boundary) is hashed; during encoding, a child hunk whose full-hunk (CRC-16, SHA-1) matches a window is emitted as a CompressionParent reference to that parent unit — mirroring MAME's chd_file_compressor parent walk (chd.cpp: hashes every parent unit window, then matches child hunks against it).

public sealed class ParentMap : IDisposable

Inheritance: object

ParentMap

Implements: IDisposable

Inherited Members: object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.ReferenceEquals(object, object)

object.ToString()

Remarks

The walk is sequential (the parent's hunks must be decompressed once; each read is cached by the reader). The map itself is read-only after construction, so it is safe to consult from the encoder's single consumer thread during the parallel pipeline.

Constructors

ParentMap(string, uint, uint)

Initializes a new parent map by decompressing and hashing the parent CHD.

public ParentMap(string parentPath, uint hunkBytes, uint unitBytes)

Parameters

parentPath string: Path of the parent CHD file.
hunkBytes uint: The hunk size of the child being created.
unitBytes uint: The unit size of the child being created.

Exceptions

ArgumentException: parentPath is null or the parent's hunk/unit sizes do not match hunkBytes/unitBytes.
IOException: The parent CHD cannot be opened.

Properties

HunkBytes

The hunk size of the parent CHD (equal to the child's).

public uint HunkBytes { get; }

Property Value

uint

HunkCount

The hunk count of the parent CHD.

public uint HunkCount { get; }

Property Value

uint

ParentSha1

The parent's overall SHA-1 (header field), stored in the child's parent-SHA-1 field.

public byte[] ParentSha1 { get; }

Property Value

byte[]

UnitBytes

The unit size of the parent CHD (equal to the child's).

public uint UnitBytes { get; }

Property Value

uint

UnitsPerHunk

The number of units per hunk.

public uint UnitsPerHunk { get; }

Property Value

uint

Methods

Dispose()

Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.

public void Dispose()

TryGetParentUnit(ushort, string, out uint)

Looks up a child hunk's (CRC-16, SHA-1) in the parent map.

public bool TryGetParentUnit(ushort crc16, string sha1Hex, out uint parentUnit)

Parameters

crc16 ushort: CRC-16 of the child hunk's data.
sha1Hex string: Hexadecimal SHA-1 of the child hunk's data.
parentUnit uint: When true is returned, the parent unit index (0-based, in units) whose data matches the child hunk.

Returns

bool: true if a matching parent unit exists; otherwise false.