/// <summary>
/// Compression using a run length encoding algorithm.
/// See MS-OVBA Section 2.4
/// </summary>
/// <param name="part">Byte array to decompress</param>
/// <returns></returns>
internal static byte[] CompressPart(byte[] part)
{
using (var ms = RecyclableMemory.GetStream(4096))
{
BinaryWriter br = new BinaryWriter(ms);
br.Write((byte)1);
int compStart = 1;
int compEnd = 4098;
int decompStart = 0;
int decompEnd = part.Length < 4096 ? part.Length : 4096;
while (decompStart < decompEnd && compStart < compEnd)
{
byte[] chunk = CompressChunk(part, ref decompStart);
ushort header;
if (chunk == null || chunk.Length == 0)
{
header = 4096 | 0x600; //B=011 A=0
}
else
{
header = (ushort)(((chunk.Length - 1) & 0xFFF));
header |= 0xB000; //B=011 A=1
br.Write(header);
br.Write(chunk);
}
decompEnd = part.Length < decompStart + 4096 ? part.Length : decompStart + 4096;
}
br.Flush();
return(ms.ToArray());
}
}
/// <summary>
/// Decompression using a run length encoding algorithm.
/// See MS-OVBA Section 2.4
/// </summary>
/// <param name="part">Byte array to decompress</param>
/// <param name="startPos"></param>
/// <returns></returns>
internal static byte[] DecompressPart(byte[] part, int startPos)
{
if (part[startPos] != 1)
{
return(null);
}
using (var ms = RecyclableMemory.GetStream(4096))
{
int compressPos = startPos + 1;
while (compressPos < part.Length - 1)
{
DecompressChunk(ms, part, ref compressPos);
}
return(ms.ToArray());
}
}