/// <summary>
/// Deallocates a previously allocated block.
/// </summary>
/// <param name="address">The address of the block to deallocate.</param>
public void Free(uint address)
{
HeapEntry entry = new HeapEntry(address, 0);
int index = blocks.BinarySearch(entry, entryComparer);
if (index >= 0)
{
// delete the block
entry = blocks[index];
blocks.RemoveAt(index);
// adjust the heap extent if necessary
if (entry.Start + entry.Length - heapAddress == heapExtent)
{
if (index == 0)
{
heapExtent = 0;
}
else
{
HeapEntry prev = blocks[index - 1];
heapExtent = prev.Start + prev.Length - heapAddress;
}
}
// add the block to the free list
index = ~freeList.BinarySearch(entry, entryComparer);
System.Diagnostics.Debug.Assert(index >= 0);
freeList.Insert(index, entry);
if (index < freeList.Count - 1)
{
Coalesce(index, index + 1);
}
if (index > 0)
{
Coalesce(index - 1, index);
}
// shrink the heap if necessary
if (blocks.Count > 0 && heapExtent <= (endMem - heapAddress) / 2)
{
if (setEndMem(heapAddress + heapExtent))
{
endMem = heapAddress + heapExtent;
for (int i = freeList.Count - 1; i >= 0; i--)
{
if (freeList[i].Start >= endMem)
{
freeList.RemoveAt(i);
}
}
}
}
}
}
private void Coalesce(int index1, int index2)
{
HeapEntry first = freeList[index1];
HeapEntry second = freeList[index2];
if (first.Start + first.Length >= second.Start)
{
first.Length = second.Start + second.Length - first.Start;
freeList[index1] = first;
freeList.RemoveAt(index2);
}
}
/// <summary>
/// Allocates a new block on the heap.
/// </summary>
/// <param name="size">The size of the new block, in bytes.</param>
/// <returns>The address of the new block, or 0 if allocation failed.</returns>
public uint Alloc(uint size)
{
HeapEntry result = new HeapEntry(0, size);
// look for a free block
if (freeList != null)
{
for (int i = 0; i < freeList.Count; i++)
{
HeapEntry entry = freeList[i];
if (entry.Length >= size)
{
result.Start = entry.Start;
if (entry.Length > size)
{
// shrink the free block
entry.Start += size;
entry.Length -= size;
freeList[i] = entry;
}
else
{
freeList.RemoveAt(i);
}
break;
}
}
}
if (result.Start == 0)
{
// enforce maximum heap size
if (maxHeapExtent != 0 && heapExtent + size > maxHeapExtent)
{
return(0);
}
// add a new block at the end
result = new HeapEntry(heapAddress + heapExtent, size);
if (heapAddress + heapExtent + size > endMem)
{
// grow the heap
uint newHeapAllocation = Math.Max(
heapExtent * 5 / 4,
heapExtent + size);
if (maxHeapExtent != 0)
{
newHeapAllocation = Math.Min(newHeapAllocation, maxHeapExtent);
}
if (setEndMem(heapAddress + newHeapAllocation))
{
endMem = heapAddress + newHeapAllocation;
}
else
{
return(0);
}
}
heapExtent += size;
}
// add the new block to the list
int index = ~blocks.BinarySearch(result, entryComparer);
System.Diagnostics.Debug.Assert(index >= 0);
blocks.Insert(index, result);
return(result.Start);
}
