Beispiel #1
0
        //Each block of compressed data begins with 3 header bits
        // containing the following data:
        //    first bit       BFINAL
        //    next 2 bits     BTYPE
        // Note that the header bits do not necessarily begin on a byte
        // boundary, since a block does not necessarily occupy an integral
        // number of bytes.
        // BFINAL is set if and only if this is the last block of the data
        // set.
        // BTYPE specifies how the data are compressed, as follows:
        //    00 - no compression
        //    01 - compressed with fixed Huffman codes
        //    10 - compressed with dynamic Huffman codes
        //    11 - reserved (error)
        // The only difference between the two compressed cases is how the
        // Huffman codes for the literal/length and distance alphabets are
        // defined.
        //
        // This function returns true for success (end of block or output window is full,)
        // false if we are short of input
        //
        private bool Decode()
        {
            bool eob    = false;
            bool result = false;

            if (Finished())
            {
                return(true);
            }

            if (hasFormatReader)
            {
                if (state == InflaterState.ReadingHeader)
                {
                    if (!formatReader.ReadHeader(input))
                    {
                        return(false);
                    }
                    state = InflaterState.ReadingBFinal;
                }
                else if (state == InflaterState.StartReadingFooter || state == InflaterState.ReadingFooter)
                {
                    if (!formatReader.ReadFooter(input))
                    {
                        return(false);
                    }

                    state = InflaterState.VerifyingFooter;
                    return(true);
                }
            }

            if (state == InflaterState.ReadingBFinal)     // reading bfinal bit
            // Need 1 bit
            {
                if (!input.EnsureBitsAvailable(1))
                {
                    return(false);
                }

                bfinal = input.GetBits(1);
                state  = InflaterState.ReadingBType;
            }

            if (state == InflaterState.ReadingBType)
            {
                // Need 2 bits
                if (!input.EnsureBitsAvailable(2))
                {
                    state = InflaterState.ReadingBType;
                    return(false);
                }

                blockType = (BlockType)input.GetBits(2);
                if (blockType == BlockType.Dynamic)
                {
                    state = InflaterState.ReadingNumLitCodes;
                }
                else if (blockType == BlockType.Static)
                {
                    literalLengthTree = HuffmanTree.StaticLiteralLengthTree;
                    distanceTree      = HuffmanTree.StaticDistanceTree;
                    state             = InflaterState.DecodeTop;
                }
                else if (blockType == BlockType.Uncompressed)
                {
                    state = InflaterState.UncompressedAligning;
                }
                else
                {
                    throw new InvalidDataException(SR.GetString(SR.UnknownBlockType));
                }
            }

            if (blockType == BlockType.Dynamic)
            {
                if (state < InflaterState.DecodeTop)     // we are reading the header
                {
                    result = DecodeDynamicBlockHeader();
                }
                else
                {
                    result = DecodeBlock(out eob);  // this can returns true when output is full
                }
            }
            else if (blockType == BlockType.Static)
            {
                result = DecodeBlock(out eob);
            }
            else if (blockType == BlockType.Uncompressed)
            {
                result = DecodeUncompressedBlock(out eob);
            }
            else
            {
                throw new InvalidDataException(SR.GetString(SR.UnknownBlockType));
            }

            //
            // If we reached the end of the block and the block we were decoding had
            // bfinal=1 (final block)
            //
            if (eob && (bfinal != 0))
            {
                if (hasFormatReader)
                {
                    state = InflaterState.StartReadingFooter;
                }
                else
                {
                    state = InflaterState.Done;
                }
            }
            return(result);
        }
Beispiel #2
0
        // Format of the dynamic block header:
        //      5 Bits: HLIT, # of Literal/Length codes - 257 (257 - 286)
        //      5 Bits: HDIST, # of Distance codes - 1        (1 - 32)
        //      4 Bits: HCLEN, # of Code Length codes - 4     (4 - 19)
        //
        //      (HCLEN + 4) x 3 bits: code lengths for the code length
        //          alphabet given just above, in the order: 16, 17, 18,
        //          0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
        //
        //          These code lengths are interpreted as 3-bit integers
        //          (0-7); as above, a code length of 0 means the
        //          corresponding symbol (literal/length or distance code
        //          length) is not used.
        //
        //      HLIT + 257 code lengths for the literal/length alphabet,
        //          encoded using the code length Huffman code
        //
        //       HDIST + 1 code lengths for the distance alphabet,
        //          encoded using the code length Huffman code
        //
        // The code length repeat codes can cross from HLIT + 257 to the
        // HDIST + 1 code lengths.  In other words, all code lengths form
        // a single sequence of HLIT + HDIST + 258 values.
        bool DecodeDynamicBlockHeader()
        {
            switch (state)
            {
            case InflaterState.ReadingNumLitCodes:
                literalLengthCodeCount = input.GetBits(5);
                if (literalLengthCodeCount < 0)
                {
                    return(false);
                }
                literalLengthCodeCount += 257;
                state = InflaterState.ReadingNumDistCodes;
                goto case InflaterState.ReadingNumDistCodes;

            case InflaterState.ReadingNumDistCodes:
                distanceCodeCount = input.GetBits(5);
                if (distanceCodeCount < 0)
                {
                    return(false);
                }
                distanceCodeCount += 1;
                state              = InflaterState.ReadingNumCodeLengthCodes;
                goto case InflaterState.ReadingNumCodeLengthCodes;

            case InflaterState.ReadingNumCodeLengthCodes:
                codeLengthCodeCount = input.GetBits(4);
                if (codeLengthCodeCount < 0)
                {
                    return(false);
                }
                codeLengthCodeCount += 4;
                loopCounter          = 0;
                state = InflaterState.ReadingCodeLengthCodes;
                goto case InflaterState.ReadingCodeLengthCodes;

            case InflaterState.ReadingCodeLengthCodes:
                while (loopCounter < codeLengthCodeCount)
                {
                    int bits = input.GetBits(3);
                    if (bits < 0)
                    {
                        return(false);
                    }
                    codeLengthTreeCodeLength[codeOrder[loopCounter]] = (byte)bits;
                    ++loopCounter;
                }

                for (int i = codeLengthCodeCount; i < codeOrder.Length; i++)
                {
                    codeLengthTreeCodeLength[codeOrder[i]] = 0;
                }

                // create huffman tree for code length
                codeLengthTree = new HuffmanTree(codeLengthTreeCodeLength);
                codeArraySize  = literalLengthCodeCount + distanceCodeCount;
                loopCounter    = 0;  // reset loop count

                state = InflaterState.ReadingTreeCodesBefore;
                goto case InflaterState.ReadingTreeCodesBefore;

            case InflaterState.ReadingTreeCodesBefore:
            case InflaterState.ReadingTreeCodesAfter:
                while (loopCounter < codeArraySize)
                {
                    if (state == InflaterState.ReadingTreeCodesBefore)
                    {
                        if ((lengthCode = codeLengthTree.GetNextSymbol(input)) < 0)
                        {
                            return(false);
                        }
                    }

                    // The alphabet for code lengths is as follows:
                    //  0 - 15: Represent code lengths of 0 - 15
                    //  16: Copy the previous code length 3 - 6 times.
                    //  The next 2 bits indicate repeat length
                    //         (0 = 3, ... , 3 = 6)
                    //      Example:  Codes 8, 16 (+2 bits 11),
                    //                16 (+2 bits 10) will expand to
                    //                12 code lengths of 8 (1 + 6 + 5)
                    //  17: Repeat a code length of 0 for 3 - 10 times.
                    //    (3 bits of length)
                    //  18: Repeat a code length of 0 for 11 - 138 times
                    //    (7 bits of length)
                    if (lengthCode <= 15)
                    {
                        codeList[loopCounter++] = (byte)lengthCode;
                    }
                    else
                    {
                        if (!input.EnsureBitsAvailable(7))   // it doesn't matter if we require more bits here
                        {
                            state = InflaterState.ReadingTreeCodesAfter;
                            return(false);
                        }

                        int repeatCount;
                        if (lengthCode == 16)
                        {
                            if (loopCounter == 0)            // can't have "prev code" on first code
                            {
                                throw new InvalidDataException();
                            }

                            byte previousCode = codeList[loopCounter - 1];
                            repeatCount = input.GetBits(2) + 3;

                            if (loopCounter + repeatCount > codeArraySize)
                            {
                                throw new InvalidDataException();
                            }

                            for (int j = 0; j < repeatCount; j++)
                            {
                                codeList[loopCounter++] = previousCode;
                            }
                        }
                        else if (lengthCode == 17)
                        {
                            repeatCount = input.GetBits(3) + 3;

                            if (loopCounter + repeatCount > codeArraySize)
                            {
                                throw new InvalidDataException();
                            }

                            for (int j = 0; j < repeatCount; j++)
                            {
                                codeList[loopCounter++] = 0;
                            }
                        }
                        else   // code == 18
                        {
                            repeatCount = input.GetBits(7) + 11;

                            if (loopCounter + repeatCount > codeArraySize)
                            {
                                throw new InvalidDataException();
                            }

                            for (int j = 0; j < repeatCount; j++)
                            {
                                codeList[loopCounter++] = 0;
                            }
                        }
                    }
                    state = InflaterState.ReadingTreeCodesBefore; // we want to read the next code.
                }
                break;

            default:
                Debug.Assert(false, "check why we are here!");
                throw new InvalidDataException(SR.GetString(SR.UnknownState));
            }

            byte[] literalTreeCodeLength  = new byte[HuffmanTree.MaxLiteralTreeElements];
            byte[] distanceTreeCodeLength = new byte[HuffmanTree.MaxDistTreeElements];

            // Create literal and distance tables
            Array.Copy(codeList, literalTreeCodeLength, literalLengthCodeCount);
            Array.Copy(codeList, literalLengthCodeCount, distanceTreeCodeLength, 0, distanceCodeCount);

            // Make sure there is an end-of-block code, otherwise how could we ever end?
            if (literalTreeCodeLength[HuffmanTree.EndOfBlockCode] == 0)
            {
                throw new InvalidDataException();
            }

            literalLengthTree = new HuffmanTree(literalTreeCodeLength);
            distanceTree      = new HuffmanTree(distanceTreeCodeLength);
            state             = InflaterState.DecodeTop;
            return(true);
        }
Beispiel #3
0
 static HuffmanTree()
 {
     // construct the static literal tree and distance tree
     staticLiteralLengthTree = new HuffmanTree(GetStaticLiteralTreeLength());
     staticDistanceTree      = new HuffmanTree(GetStaticDistanceTreeLength());
 }