Initial commit

LibDgf/Aqualead/AlLzDecoder.cs

@@ -0,0 +1,114 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+
+namespace LibDgf.Aqualead
+{
+    public class AlLzDecoder
+    {
+        uint bitBuffer;
+        int numBitsRemaining;
+        BinaryReader br;
+
+        public byte[] Decode(Stream inStream)
+        {
+            br = new BinaryReader(inStream);
+            numBitsRemaining = 0;
+
+            if (new string(br.ReadChars(4)) != "ALLZ")
+                throw new InvalidDataException("Not an Aqualead LZ compressed file.");
+            byte version = br.ReadByte();
+            if (version > 1)
+                throw new InvalidDataException("Version too new.");
+
+            byte minLookbackLengthBits = br.ReadByte();
+            byte minLookbackPosBits = br.ReadByte();
+            byte minLiteralLengthBits = br.ReadByte();
+            uint decompressedLength = br.ReadUInt32();
+
+            byte[] output = new byte[decompressedLength];
+            int outPos = 0;
+
+            if (version == 0) ReadBits(1); // Consume literal bit if v0
+            bool hasLiteral = true;
+
+            while (true)
+            {
+                if (hasLiteral)
+                {
+                    if (outPos >= decompressedLength) break;
+                    int literalLength = (int)ReadEncodedNum(minLiteralLengthBits) + 1;
+                    if (inStream.Read(output, outPos, literalLength) != literalLength)
+                        throw new IOException("Could not read all bytes requested.");
+                    outPos += literalLength;
+                    //Console.WriteLine("Did literal");
+                }
+
+                if (outPos >= decompressedLength) break;
+                int lookbackPos = (int)ReadEncodedNum(minLookbackPosBits) + 1;
+                int lookbackLength = (int)ReadEncodedNum(minLookbackLengthBits) + 3;
+
+                for (int i = 0; i < lookbackLength; ++i)
+                {
+                    output[outPos] = output[outPos - lookbackPos];
+                    ++outPos;
+                }
+                //Console.WriteLine("Did lookback");
+
+                if (outPos >= decompressedLength) break;
+                hasLiteral = ReadBits(1) == 0;
+                //Console.WriteLine("Has literal: " + hasLiteral);
+            }
+
+            br = null;
+            return output;
+        }
+
+        uint ReadEncodedNum(int minNumBits)
+        {
+            int numExtBits = CountBits();
+            uint num = ReadBits(minNumBits);
+            if (numExtBits > 0)
+            {
+                // Length encoding
+                // e e e e 0 | xxxx | yy
+                // Number of es indicate exponent and number of bits for mantissa
+                // Subsequently, ((2 ^ count(e)) - 1 + xxxx) | yy
+                num |= (uint)(ReadBits(numExtBits) + (1 << numExtBits) - 1) << minNumBits;
+            }
+            return num;
+        }
+
+        void EnsureBits(int numBits)
+        {
+            while (numBitsRemaining < numBits)
+            {
+                if (numBitsRemaining + 8 > 32) throw new ArgumentOutOfRangeException(nameof(numBits));
+                bitBuffer |= (uint)br.ReadByte() << numBitsRemaining;
+                numBitsRemaining += 8;
+            }
+        }
+
+        uint ReadBits(int numBits)
+        {
+            EnsureBits(numBits);
+            uint output = (uint)(bitBuffer & ((1 << numBits) - 1));
+            bitBuffer >>= numBits;
+            numBitsRemaining -= numBits;
+            return output;
+        }
+
+        int CountBits()
+        {
+            int i = 0;
+            while (ReadBits(1) != 0) ++i;
+            return i;
+        }
+
+        void WriteBits()
+        {
+
+        }
+    }
+}