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89 lines
3.9 KiB
C#
89 lines
3.9 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Text;
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namespace DSDecmp.Formats
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{
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/// <summary>
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/// The LZ-Overlay compression format. Compresses part of the file from end to start.
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/// Is used for the 'overlay' files in NDS games, as well as arm9.bin.
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/// Note that the last 12 bytes should not be included in the 'inLength' argument when
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/// decompressing arm9.bin.
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/// </summary>
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public class LZOvl : CompressionFormat
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{
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#region Method: Supports(Stream, long)
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public override bool Supports(System.IO.Stream stream, long inLength)
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{
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// assume the 'inLength' does not include the 12 bytes at the end of arm9.bin
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// only allow integer-sized files
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if (inLength > 0xFFFFFFFFL)
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return false;
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// the header is 4 bytes minimum
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if (inLength < 4)
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return false;
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long streamStart = stream.Position;
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byte[] header = new byte[Math.Min(inLength, 0x20)];
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stream.Position += inLength - header.Length;
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stream.Read(header, 0, header.Length);
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// reset the stream
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stream.Position = streamStart;
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uint extraSize = IOUtils.ToNDSu32(header, header.Length - 4);
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if (extraSize == 0)
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return true;
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// if the extrasize is nonzero, the minimum header length is 8 bytes
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if (header.Length < 8)
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return false;
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byte headerLen = header[header.Length - 5];
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if (inLength < headerLen)
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return false;
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// the compressed length should fit in the input file
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int compressedLen = header[header.Length - 6] << 16
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| header[header.Length - 7] << 8
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| header[header.Length - 8];
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if (compressedLen >= inLength - headerLen)
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return false;
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// verify that the rest of the header is filled with 0xFF
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for (int i = header.Length - 9; i >= header.Length - headerLen; i--)
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if (header[i] != 0xFF)
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return false;
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return true;
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}
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#endregion
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public override void Decompress(System.IO.Stream instream, long inLength, System.IO.Stream outstream)
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{
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// Overlay LZ compression is basically just LZ-0x10 compression.
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// however the order if reading is reversed: the compression starts at the end of the file.
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// Assuming we start reading at the end towards the beginning, the format is:
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/*
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* u32 extraSize; // decompressed data size = file length (including header) + this value
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* u8 headerSize;
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* u24 compressedLength; // can be less than file size (w/o header). If so, the rest of the file is uncompressed.
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* u8[headerSize-8] padding; // 0xFF-s
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*
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* 0x10-like-compressed data follows (without the usual 4-byte header).
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* The only difference is that 2 should be added to the DISP value in compressed blocks
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* to get the proper value.
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* the u32 and u24 are read most significant byte first.
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* if extraSize is 0, there is no headerSize, decompressedLength or padding.
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* the data starts immediately, and is uncompressed.
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*
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* arm9.bin has 3 extra u32 values at the 'start' (ie: end of the file),
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* which may be ignored. (and are ignored here) These 12 bytes also should not
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* be included in the computation of the output size.
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*/
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throw new NotImplementedException();
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}
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public override int Compress(System.IO.Stream instream, long inLength, System.IO.Stream outstream)
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{
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throw new NotImplementedException();
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}
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}
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}
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