public int GetFreeListEntryIndex()
{
AllocationTableEntry freeList = ReadEntry(FreeListEntryIndex);
return(freeList.GetNext());
}
/// <summary>
/// Splits a single list segment into 2 segments. The sequence of blocks in the full list will remain the same.
/// </summary>
/// <param name="segmentBlockIndex">The block index of the segment to split.</param>
/// <param name="firstSubSegmentLength">The length of the first subsegment.</param>
public void Split(int segmentBlockIndex, int firstSubSegmentLength)
{
Debug.Assert(firstSubSegmentLength > 0);
int segAIndex = BlockToEntryIndex(segmentBlockIndex);
AllocationTableEntry segA = ReadEntry(segAIndex);
if (!segA.IsMultiBlockSegment())
{
throw new ArgumentException("Cannot split a single-entry segment.");
}
AllocationTableEntry segARange = ReadEntry(segAIndex + 1);
int originalLength = segARange.GetNext() - segARange.GetPrev() + 1;
if (firstSubSegmentLength >= originalLength)
{
throw new ArgumentOutOfRangeException(nameof(firstSubSegmentLength),
$"Requested sub-segment length ({firstSubSegmentLength}) must be less than the full segment length ({originalLength})");
}
int segBIndex = segAIndex + firstSubSegmentLength;
int segALength = firstSubSegmentLength;
int segBLength = originalLength - segALength;
var segB = new AllocationTableEntry();
// Insert segment B between segments A and C
segB.SetPrev(segAIndex);
segB.SetNext(segA.GetNext());
segA.SetNext(segBIndex);
if (!segB.IsListEnd())
{
AllocationTableEntry segC = ReadEntry(segB.GetNext());
segC.SetPrev(segBIndex);
WriteEntry(segB.GetNext(), segC);
}
// Write the new range entries if needed
if (segBLength > 1)
{
segB.MakeMultiBlockSegment();
var segBRange = new AllocationTableEntry();
segBRange.SetRange(segBIndex, segBIndex + segBLength - 1);
WriteEntry(segBIndex + 1, segBRange);
WriteEntry(segBIndex + segBLength - 1, segBRange);
}
WriteEntry(segBIndex, segB);
if (segALength == 1)
{
segA.MakeSingleBlockSegment();
}
else
{
segARange.SetRange(segAIndex, segAIndex + segALength - 1);
WriteEntry(segAIndex + 1, segARange);
WriteEntry(segAIndex + segALength - 1, segARange);
}
WriteEntry(segAIndex, segA);
}
