/// <summary>
/// Reconstitutes a changed block of memory by applying a compressed
/// set of differences to the original block from the game file.
/// </summary>
/// <param name="original">The original block of memory.</param>
/// <param name="delta">The RLE-compressed set of differences,
/// prefixed with a 4-byte length. This length may be larger than
/// the original block, but not smaller.</param>
/// <returns>The changed block of memory. The length of this array is
/// specified at the beginning of <paramref name="delta"/>.</returns>
public static byte[] DecompressMemory(byte[] original, byte[] delta)
{
MemoryStream mstr = new MemoryStream(delta);
uint length = BigEndian.ReadInt32(mstr);
if (length < original.Length)
{
throw new ArgumentException("Compressed block's length tag must be no less than original block's size");
}
byte[] result = new byte[length];
int rp = 0;
for (int i = 4; i < delta.Length; i++)
{
byte b = delta[i];
if (b == 0)
{
int repeats = delta[++i] + 1;
Array.Copy(original, rp, result, rp, repeats);
rp += repeats;
}
else
{
result[rp] = (byte)(original[rp] ^ b);
rp++;
}
}
while (rp < original.Length)
{
result[rp] = original[rp];
rp++;
}
return(result);
}
/// <summary>
/// Initializes a new allocator from a previous saved heap state.
/// </summary>
/// <param name="savedHeap">A byte array describing the heap state,
/// as returned by the <see cref="Save"/> method.</param>
/// <param name="requester">A delegate to request more memory.</param>
public HeapAllocator(byte[] savedHeap, MemoryRequester requester)
{
this.heapAddress = BigEndian.ReadInt32(savedHeap, 0);
this.setEndMem = requester;
this.blocks = new List <HeapEntry>();
this.freeList = new List <HeapEntry>();
uint numBlocks = BigEndian.ReadInt32(savedHeap, 4);
blocks.Capacity = (int)numBlocks;
uint nextAddress = heapAddress;
for (uint i = 0; i < numBlocks; i++)
{
uint start = BigEndian.ReadInt32(savedHeap, 8 * i + 8);
uint length = BigEndian.ReadInt32(savedHeap, 8 * i + 12);
blocks.Add(new HeapEntry(start, length));
if (nextAddress < start)
{
freeList.Add(new HeapEntry(nextAddress, start - nextAddress));
}
nextAddress = start + length;
}
endMem = nextAddress;
heapExtent = nextAddress - heapAddress;
if (setEndMem(endMem) == false)
{
throw new ArgumentException("Can't allocate VM memory to fit saved heap");
}
blocks.Sort(entryComparer);
freeList.Sort(entryComparer);
}
/// <summary>
/// Writes the chunks to a Quetzal file.
/// </summary>
/// <param name="stream">The stream to write to.</param>
public void WriteToStream(Stream stream)
{
BigEndian.WriteInt32(stream, FORM); // IFF tag
BigEndian.WriteInt32(stream, 0); // file length (filled in later)
BigEndian.WriteInt32(stream, IFZS); // FORM sub-ID for Quetzal
uint totalSize = 4; // includes sub-ID
foreach (KeyValuePair <uint, byte[]> pair in chunks)
{
BigEndian.WriteInt32(stream, pair.Key); // chunk type
BigEndian.WriteInt32(stream, (uint)pair.Value.Length); // chunk length
stream.Write(pair.Value, 0, pair.Value.Length); // chunk data
totalSize += 8 + (uint)(pair.Value.Length);
}
if (totalSize % 2 == 1)
{
stream.WriteByte(0); // padding (not counted in file length)
}
stream.Seek(4, SeekOrigin.Begin);
BigEndian.WriteInt32(stream, totalSize);
//stream.SetLength(totalSize);
}
/// <summary>
/// Reads a big-endian double word from memory.
/// </summary>
/// <param name="offset">The address to read from.</param>
/// <returns>The 32-bit value at the specified address.</returns>
public uint ReadInt32(uint offset)
{
return(BigEndian.ReadInt32(memory, offset));
}
/// <summary>
/// Reads a big-endian word from memory.
/// </summary>
/// <param name="offset">The address to read from</param>
/// <returns>The word at the specified address.</returns>
public ushort ReadInt16(uint offset)
{
return(BigEndian.ReadInt16(memory, offset));
}