ImageSharp/src/ImageProcessor/Formats/Png/Zlib/InflaterDynHeader.cs

namespace ImageProcessor.Formats
{
    using System;

    class InflaterDynHeader
    {
        #region Constants
        const int LNUM = 0;
        const int DNUM = 1;
        const int BLNUM = 2;
        const int BLLENS = 3;
        const int LENS = 4;
        const int REPS = 5;

        static readonly int[] repMin = { 3, 3, 11 };
        static readonly int[] repBits = { 2, 3, 7 };

        static readonly int[] BL_ORDER =
        { 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15 };

        #endregion

        #region Constructors
        public InflaterDynHeader()
        {
        }
        #endregion

        public bool Decode(StreamManipulator input)
        {
            decode_loop:
            for (;;)
            {
                switch (mode)
                {
                    case LNUM:
                        lnum = input.PeekBits(5);
                        if (lnum < 0)
                        {
                            return false;
                        }
                        lnum += 257;
                        input.DropBits(5);
                        //  	    System.err.println("LNUM: "+lnum);
                        mode = DNUM;
                        goto case DNUM; // fall through
                    case DNUM:
                        dnum = input.PeekBits(5);
                        if (dnum < 0)
                        {
                            return false;
                        }
                        dnum++;
                        input.DropBits(5);
                        //  	    System.err.println("DNUM: "+dnum);
                        num = lnum + dnum;
                        litdistLens = new byte[num];
                        mode = BLNUM;
                        goto case BLNUM; // fall through
                    case BLNUM:
                        blnum = input.PeekBits(4);
                        if (blnum < 0)
                        {
                            return false;
                        }
                        blnum += 4;
                        input.DropBits(4);
                        blLens = new byte[19];
                        ptr = 0;
                        //  	    System.err.println("BLNUM: "+blnum);
                        mode = BLLENS;
                        goto case BLLENS; // fall through
                    case BLLENS:
                        while (ptr < blnum)
                        {
                            int len = input.PeekBits(3);
                            if (len < 0)
                            {
                                return false;
                            }
                            input.DropBits(3);
                            //  		System.err.println("blLens["+BL_ORDER[ptr]+"]: "+len);
                            blLens[BL_ORDER[ptr]] = (byte)len;
                            ptr++;
                        }
                        blTree = new InflaterHuffmanTree(blLens);
                        blLens = null;
                        ptr = 0;
                        mode = LENS;
                        goto case LENS; // fall through
                    case LENS:
                        {
                            int symbol;
                            while (((symbol = blTree.GetSymbol(input)) & ~15) == 0)
                            {
                                /* Normal case: symbol in [0..15] */

                                //  		  System.err.println("litdistLens["+ptr+"]: "+symbol);
                                litdistLens[ptr++] = lastLen = (byte)symbol;

                                if (ptr == num)
                                {
                                    /* Finished */
                                    return true;
                                }
                            }

                            /* need more input ? */
                            if (symbol < 0)
                            {
                                return false;
                            }

                            /* otherwise repeat code */
                            if (symbol >= 17)
                            {
                                /* repeat zero */
                                //  		  System.err.println("repeating zero");
                                lastLen = 0;
                            }
                            else
                            {
                                if (ptr == 0)
                                {
                                    throw new ImageFormatException();
                                }
                            }
                            repSymbol = symbol - 16;
                        }
                        mode = REPS;
                        goto case REPS; // fall through
                    case REPS:
                        {
                            int bits = repBits[repSymbol];
                            int count = input.PeekBits(bits);
                            if (count < 0)
                            {
                                return false;
                            }
                            input.DropBits(bits);
                            count += repMin[repSymbol];
                            //  	      System.err.println("litdistLens repeated: "+count);

                            if (ptr + count > num)
                            {
                                throw new ImageFormatException();
                            }
                            while (count-- > 0)
                            {
                                litdistLens[ptr++] = lastLen;
                            }

                            if (ptr == num)
                            {
                                /* Finished */
                                return true;
                            }
                        }
                        mode = LENS;
                        goto decode_loop;
                }
            }
        }

        public InflaterHuffmanTree BuildLitLenTree()
        {
            byte[] litlenLens = new byte[lnum];
            Array.Copy(litdistLens, 0, litlenLens, 0, lnum);
            return new InflaterHuffmanTree(litlenLens);
        }

        public InflaterHuffmanTree BuildDistTree()
        {
            byte[] distLens = new byte[dnum];
            Array.Copy(litdistLens, lnum, distLens, 0, dnum);
            return new InflaterHuffmanTree(distLens);
        }

        #region Instance Fields
        byte[] blLens;
        byte[] litdistLens;

        InflaterHuffmanTree blTree;

        /// <summary>
        /// The current decode mode
        /// </summary>
		int mode;
        int lnum, dnum, blnum, num;
        int repSymbol;
        byte lastLen;
        int ptr;
        #endregion

    }
}