/// <summary>
/// Gets the optimal compression lengths for each start of a compressed block using Dynamic Programming.
/// This takes O(n^2) time, although in practice it will often be O(n^3) since one of the constants is 0x10110
/// (the maximum length of a compressed block)
/// </summary>
/// <param name="indata">The data to compress.</param>
/// <param name="inLength">The length of the data to compress.</param>
/// <param name="lengths">The optimal 'length' of the compressed blocks. For each byte in the input data,
/// this value is the optimal 'length' value. If it is 1, the block should not be compressed.</param>
/// <param name="disps">The 'disp' values of the compressed blocks. May be 0, in which case the
/// corresponding length will never be anything other than 1.</param>
internal static unsafe void GetOptimalCompressionLengths(byte *indata, int inLength, out int[] lengths, out int[] disps)
{
lengths = new int[inLength];
disps = new int[inLength];
int[] minLengths = new int[inLength];
for (int i = inLength - 1; i >= 0; i--)
{
// first get the compression length when the next byte is not compressed
minLengths[i] = int.MaxValue;
lengths[i] = 1;
if (i + 1 >= inLength)
{
minLengths[i] = 1;
}
else
{
minLengths[i] = 1 + minLengths[i + 1];
}
// then the optimal compressed length
int oldLength = Math.Min(0x1000, i);
// get the appropriate disp while at it. Takes at most O(n) time if oldLength is considered O(n) and 0x10110 constant.
// however since a lot of files will not be larger than 0x10110, this will often take ~O(n^2) time.
// be sure to bound the input length with 0x10110, as that's the maximum length for LZ-11 compressed blocks.
int maxLen = LZUtil.GetOccurrenceLength(indata + i, Math.Min(inLength - i, 0x10110),
indata + i - oldLength, oldLength, out disps[i]);
if (disps[i] > i)
{
throw new Exception("disp is too large");
}
for (int j = 3; j <= maxLen; j++)
{
int blocklen;
if (j > 0x110)
{
blocklen = 4;
}
else if (j > 0x10)
{
blocklen = 3;
}
else
{
blocklen = 2;
}
int newCompLen;
if (i + j >= inLength)
{
newCompLen = blocklen;
}
else
{
newCompLen = blocklen + minLengths[i + j];
}
if (newCompLen < minLengths[i])
{
lengths[i] = j;
minLengths[i] = newCompLen;
}
}
}
// we could optimize this further to also optimize it with regard to the flag-bytes, but that would require 8 times
// more space and time (one for each position in the block) for only a potentially tiny increase in compression ratio.
}
/// <summary>
/// Compresses the input using the 'original', unoptimized compression algorithm.
/// This algorithm should yield files that are the same as those found in the games.
/// (delegates to the optimized method if LookAhead is set)
/// </summary>
internal static unsafe int Compress(Stream instream, long inLength, Stream outstream, bool original)
{
// make sure the decompressed size fits in 3 bytes.
// There should be room for four bytes, however I'm not 100% sure if that can be used
// in every game, as it may not be a built-in function.
if (inLength > 0xFFFFFF)
{
throw new InputTooLargeException();
}
// use the other method if lookahead is enabled
if (!original)
{
return(CompressWithLA(instream, inLength, 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 StreamTooShortException();
}
// 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.
// (a block is at most 4 bytes long)
byte[] outbuffer = new byte[(8 * 4) + 1];
outbuffer[0] = 0;
int bufferlength = 1, bufferedBlocks = 0;
int readBytes = 0;
while (readBytes < inLength)
{
#region If 8 blocks are bufferd, write them and reset the buffer
// 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;
}
#endregion
// determine if we're dealing with a compressed or raw block.
// it is a compressed block when the next 3 or more bytes can be copied from
// somewhere in the set of already compressed bytes.
int oldLength = Math.Min(readBytes, 0x1000);
int length = LZUtil.GetOccurrenceLength(instart + readBytes, (int)Math.Min(inLength - readBytes, 0x10110),
instart + readBytes - oldLength, oldLength, out var disp);
// length not 3 or more? next byte is raw data
if (length < 3)
{
outbuffer[bufferlength++] = *(instart + readBytes++);
}
else
{
// 3 or more bytes can be copied? next (length) bytes will be compressed into 2 bytes
readBytes += length;
// mark the next block as compressed
outbuffer[0] |= (byte)(1 << (7 - bufferedBlocks));
if (length > 0x110)
{
// case 1: 1(B CD E)(F GH) + (0x111)(0x1) = (LEN)(DISP)
outbuffer[bufferlength] = 0x10;
outbuffer[bufferlength] |= (byte)(((length - 0x111) >> 12) & 0x0F);
bufferlength++;
outbuffer[bufferlength] = (byte)(((length - 0x111) >> 4) & 0xFF);
bufferlength++;
outbuffer[bufferlength] = (byte)(((length - 0x111) << 4) & 0xF0);
}
else if (length > 0x10)
{
// case 0; 0(B C)(D EF) + (0x11)(0x1) = (LEN)(DISP)
outbuffer[bufferlength] = 0x00;
outbuffer[bufferlength] |= (byte)(((length - 0x111) >> 4) & 0x0F);
bufferlength++;
outbuffer[bufferlength] = (byte)(((length - 0x111) << 4) & 0xF0);
}
else
{
// case > 1: (A)(B CD) + (0x1)(0x1) = (LEN)(DISP)
outbuffer[bufferlength] = (byte)(((length - 1) << 4) & 0xF0);
}
// the last 1.5 bytes are always the disp
outbuffer[bufferlength] |= (byte)(((disp - 1) >> 8) & 0x0F);
bufferlength++;
outbuffer[bufferlength] = (byte)((disp - 1) & 0xFF);
bufferlength++;
}
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);
}