public static unsafe int CompressWithLA(Stream instream, long inLength, Stream outstream)
{
// save the input data in an array to prevent having to go back and forth in a file
byte[] indata = new byte[inLength];
int numReadBytes = instream.Read(indata, 0, (int)inLength);
if (numReadBytes != inLength)
throw new IOException();
// write the compression header first
outstream.WriteByte(0x11);
outstream.WriteByte((byte)(inLength & 0xFF));
outstream.WriteByte((byte)((inLength >> 8) & 0xFF));
outstream.WriteByte((byte)((inLength >> 16) & 0xFF));
int compressedLength = 4;
fixed (byte* instart = &indata[0])
{
// we do need to buffer the output, as the first byte indicates which blocks are compressed.
// this version does not use a look-ahead, so we do not need to buffer more than 8 blocks at a time.
// blocks are at most 4 bytes long.
byte[] outbuffer = new byte[8 * 4 + 1];
outbuffer[0] = 0;
int bufferlength = 1, bufferedBlocks = 0;
int readBytes = 0;
// get the optimal choices for len and disp
int[] lengths, disps;
GetOptimalCompressionLengths(instart, indata.Length, out lengths, out disps);
while (readBytes < inLength)
{
// we can only buffer 8 blocks at a time.
if (bufferedBlocks == 8)
{
outstream.Write(outbuffer, 0, bufferlength);
compressedLength += bufferlength;
// reset the buffer
outbuffer[0] = 0;
bufferlength = 1;
bufferedBlocks = 0;
}
if (lengths[readBytes] == 1)
{
outbuffer[bufferlength++] = *(instart + (readBytes++));
}
else
{
// mark the next block as compressed
outbuffer[0] |= (byte)(1 << (7 - bufferedBlocks));
if (lengths[readBytes] > 0x110)
{
// case 1: 1(B CD E)(F GH) + (0x111)(0x1) = (LEN)(DISP)
outbuffer[bufferlength] = 0x10;
outbuffer[bufferlength] |= (byte)(((lengths[readBytes] - 0x111) >> 12) & 0x0F);
bufferlength++;
outbuffer[bufferlength] = (byte)(((lengths[readBytes] - 0x111) >> 4) & 0xFF);
bufferlength++;
outbuffer[bufferlength] = (byte)(((lengths[readBytes] - 0x111) << 4) & 0xF0);
}
else if (lengths[readBytes] > 0x10)
{
// case 0; 0(B C)(D EF) + (0x11)(0x1) = (LEN)(DISP)
outbuffer[bufferlength] = 0x00;
outbuffer[bufferlength] |= (byte)(((lengths[readBytes] - 0x111) >> 4) & 0x0F);
bufferlength++;
outbuffer[bufferlength] = (byte)(((lengths[readBytes] - 0x111) << 4) & 0xF0);
}
else
{
// case > 1: (A)(B CD) + (0x1)(0x1) = (LEN)(DISP)
outbuffer[bufferlength] = (byte)(((lengths[readBytes] - 1) << 4) & 0xF0);
}
// the last 1.5 bytes are always the disp
outbuffer[bufferlength] |= (byte)(((disps[readBytes] - 1) >> 8) & 0x0F);
bufferlength++;
outbuffer[bufferlength] = (byte)((disps[readBytes] - 1) & 0xFF);
bufferlength++;
readBytes += lengths[readBytes];
}
bufferedBlocks++;
}
// copy the remaining blocks to the output
if (bufferedBlocks > 0)
{
outstream.Write(outbuffer, 0, bufferlength);
compressedLength += bufferlength;
/*/ make the compressed file 4-byte aligned.
while ((compressedLength % 4) != 0)
{
outstream.WriteByte(0);
compressedLength++;
}/**/
}
}
return compressedLength;
}
