Encoder and Decoder for ZLIB and DEFLATE (IETF RFC1950 and RFC1951).
This class compresses and decompresses data according to the Deflate algorithm and optionally, the ZLIB format, as documented in RFC 1950 - ZLIB and RFC 1951 - DEFLATE.
 internal int Initialize(ZlibCodec codec, CompressionLevel level, int bits, CompressionStrategy compressionStrategy)
 {
     return Initialize(codec, level, bits, MEM_LEVEL_DEFAULT, compressionStrategy);
 }
        internal int Initialize(ZlibCodec codec, CompressionLevel level, int windowBits, int memLevel, CompressionStrategy strategy)
        {
            _codec = codec;
            _codec.Message = null;

            // validation
            if (windowBits < 9 || windowBits > 15)
                throw new ZlibException("windowBits must be in the range 9..15.");

            if (memLevel < 1 || memLevel > MEM_LEVEL_MAX)
                throw new ZlibException(String.Format("memLevel must be in the range 1.. {0}", MEM_LEVEL_MAX));

            _codec.dstate = this;

            w_bits = windowBits;
            w_size = 1 << w_bits;
            w_mask = w_size - 1;

            hash_bits = memLevel + 7;
            hash_size = 1 << hash_bits;
            hash_mask = hash_size - 1;
            hash_shift = ((hash_bits + MIN_MATCH - 1) / MIN_MATCH);

            window = new byte[w_size * 2];
            prev = new short[w_size];
            head = new short[hash_size];

            // for memLevel==8, this will be 16384, 16k
            lit_bufsize = 1 << (memLevel + 6);

            // Use a single array as the buffer for data pending compression,
            // the output distance codes, and the output length codes (aka tree).
            // orig comment: This works just fine since the average
            // output size for (length,distance) codes is <= 24 bits.
            pending = new byte[lit_bufsize * 4];
            _distanceOffset = lit_bufsize;
            _lengthOffset = (1 + 2) * lit_bufsize;

            // So, for memLevel 8, the length of the pending buffer is 65536. 64k.
            // The first 16k are pending bytes.
            // The middle slice, of 32k, is used for distance codes.
            // The final 16k are length codes.

            this.compressionLevel = level;
            this.compressionStrategy = strategy;

            Reset();
            return ZlibConstants.Z_OK;
        }
        private InflateBlockMode mode; // current inflate_block mode

        #endregion Fields

        #region Constructors

        internal InflateBlocks(ZlibCodec codec, System.Object checkfn, int w)
        {
            _codec = codec;
            hufts = new int[MANY * 3];
            window = new byte[w];
            end = w;
            this.checkfn = checkfn;
            mode = InflateBlockMode.TYPE;
            Reset();
        }
 internal int Initialize(ZlibCodec codec, CompressionLevel level)
 {
     return Initialize(codec, level, ZlibConstants.WindowBitsMax);
 }
        internal int Initialize(ZlibCodec codec, int w)
        {
            _codec = codec;
            _codec.Message = null;
            blocks = null;

            // handle undocumented nowrap option (no zlib header or check)
            //nowrap = 0;
            //if (w < 0)
            //{
            //    w = - w;
            //    nowrap = 1;
            //}

            // set window size
            if (w < 8 || w > 15)
            {
                End();
                throw new ZlibException("Bad window size.");

                //return ZlibConstants.Z_STREAM_ERROR;
            }
            wbits = w;

            blocks = new InflateBlocks(codec,
                HandleRfc1950HeaderBytes ? this : null,
                1 << w);

            // reset state
            Reset();
            return ZlibConstants.Z_OK;
        }
 // Returns true if inflate is currently at the end of a block generated
 // by Z_SYNC_FLUSH or Z_FULL_FLUSH. This function is used by one PPP
 // implementation to provide an additional safety check. PPP uses Z_SYNC_FLUSH
 // but removes the length bytes of the resulting empty stored block. When
 // decompressing, PPP checks that at the end of input packet, inflate is
 // waiting for these length bytes.
 internal int SyncPoint(ZlibCodec z)
 {
     return blocks.SyncPoint();
 }
        // Called with number of bytes left to write in window at least 258
        // (the maximum string length) and number of input bytes available
        // at least ten.  The ten bytes are six bytes for the longest length/
        // distance pair plus four bytes for overloading the bit buffer.
        internal int InflateFast(int bl, int bd, int[] tl, int tl_index, int[] td, int td_index, InflateBlocks s, ZlibCodec z)
        {
            int t;        // temporary pointer
            int[] tp;     // temporary pointer
            int tp_index; // temporary pointer
            int e;        // extra bits or operation
            int b;        // bit buffer
            int k;        // bits in bit buffer
            int p;        // input data pointer
            int n;        // bytes available there
            int q;        // output window write pointer
            int m;        // bytes to end of window or read pointer
            int ml;       // mask for literal/length tree
            int md;       // mask for distance tree
            int c;        // bytes to copy
            int d;        // distance back to copy from
            int r;        // copy source pointer

            int tp_index_t_3; // (tp_index+t)*3

            // load input, output, bit values
            p = z.NextIn; n = z.AvailableBytesIn; b = s.bitb; k = s.bitk;
            q = s.writeAt; m = q < s.readAt ? s.readAt - q - 1 : s.end - q;

            // initialize masks
            ml = InternalInflateConstants.InflateMask[bl];
            md = InternalInflateConstants.InflateMask[bd];

            // do until not enough input or output space for fast loop
            do
            {
                // assume called with m >= 258 && n >= 10
                // get literal/length code
                while (k < (20))
                {
                    // max bits for literal/length code
                    n--;
                    b |= (z.InputBuffer[p++] & 0xff) << k; k += 8;
                }

                t = b & ml;
                tp = tl;
                tp_index = tl_index;
                tp_index_t_3 = (tp_index + t) * 3;
                if ((e = tp[tp_index_t_3]) == 0)
                {
                    b >>= (tp[tp_index_t_3 + 1]); k -= (tp[tp_index_t_3 + 1]);

                    s.window[q++] = (byte)tp[tp_index_t_3 + 2];
                    m--;
                    continue;
                }
                do
                {

                    b >>= (tp[tp_index_t_3 + 1]); k -= (tp[tp_index_t_3 + 1]);

                    if ((e & 16) != 0)
                    {
                        e &= 15;
                        c = tp[tp_index_t_3 + 2] + ((int)b & InternalInflateConstants.InflateMask[e]);

                        b >>= e; k -= e;

                        // decode distance base of block to copy
                        while (k < 15)
                        {
                            // max bits for distance code
                            n--;
                            b |= (z.InputBuffer[p++] & 0xff) << k; k += 8;
                        }

                        t = b & md;
                        tp = td;
                        tp_index = td_index;
                        tp_index_t_3 = (tp_index + t) * 3;
                        e = tp[tp_index_t_3];

                        do
                        {

                            b >>= (tp[tp_index_t_3 + 1]); k -= (tp[tp_index_t_3 + 1]);

                            if ((e & 16) != 0)
                            {
                                // get extra bits to add to distance base
                                e &= 15;
                                while (k < e)
                                {
                                    // get extra bits (up to 13)
                                    n--;
                                    b |= (z.InputBuffer[p++] & 0xff) << k; k += 8;
                                }

                                d = tp[tp_index_t_3 + 2] + (b & InternalInflateConstants.InflateMask[e]);

                                b >>= e; k -= e;

                                // do the copy
                                m -= c;
                                if (q >= d)
                                {
                                    // offset before dest
                                    //  just copy
                                    r = q - d;
                                    if (q - r > 0 && 2 > (q - r))
                                    {
                                        s.window[q++] = s.window[r++]; // minimum count is three,
                                        s.window[q++] = s.window[r++]; // so unroll loop a little
                                        c -= 2;
                                    }
                                    else
                                    {
                                        Array.Copy(s.window, r, s.window, q, 2);
                                        q += 2; r += 2; c -= 2;
                                    }
                                }
                                else
                                {
                                    // else offset after destination
                                    r = q - d;
                                    do
                                    {
                                        r += s.end; // force pointer in window
                                    }
                                    while (r < 0); // covers invalid distances
                                    e = s.end - r;
                                    if (c > e)
                                    {
                                        // if source crosses,
                                        c -= e; // wrapped copy
                                        if (q - r > 0 && e > (q - r))
                                        {
                                            do
                                            {
                                                s.window[q++] = s.window[r++];
                                            }
                                            while (--e != 0);
                                        }
                                        else
                                        {
                                            Array.Copy(s.window, r, s.window, q, e);
                                            q += e; r += e; e = 0;
                                        }
                                        r = 0; // copy rest from start of window
                                    }
                                }

                                // copy all or what's left
                                if (q - r > 0 && c > (q - r))
                                {
                                    do
                                    {
                                        s.window[q++] = s.window[r++];
                                    }
                                    while (--c != 0);
                                }
                                else
                                {
                                    Array.Copy(s.window, r, s.window, q, c);
                                    q += c; r += c; c = 0;
                                }
                                break;
                            }
                            else if ((e & 64) == 0)
                            {
                                t += tp[tp_index_t_3 + 2];
                                t += (b & InternalInflateConstants.InflateMask[e]);
                                tp_index_t_3 = (tp_index + t) * 3;
                                e = tp[tp_index_t_3];
                            }
                            else
                            {
                                z.Message = "invalid distance code";

                                c = z.AvailableBytesIn - n; c = (k >> 3) < c ? k >> 3 : c; n += c; p -= c; k -= (c << 3);

                                s.bitb = b; s.bitk = k;
                                z.AvailableBytesIn = n; z.TotalBytesIn += p - z.NextIn; z.NextIn = p;
                                s.writeAt = q;

                                return ZlibConstants.Z_DATA_ERROR;
                            }
                        }
                        while (true);
                        break;
                    }

                    if ((e & 64) == 0)
                    {
                        t += tp[tp_index_t_3 + 2];
                        t += (b & InternalInflateConstants.InflateMask[e]);
                        tp_index_t_3 = (tp_index + t) * 3;
                        if ((e = tp[tp_index_t_3]) == 0)
                        {
                            b >>= (tp[tp_index_t_3 + 1]); k -= (tp[tp_index_t_3 + 1]);
                            s.window[q++] = (byte)tp[tp_index_t_3 + 2];
                            m--;
                            break;
                        }
                    }
                    else if ((e & 32) != 0)
                    {
                        c = z.AvailableBytesIn - n; c = (k >> 3) < c ? k >> 3 : c; n += c; p -= c; k -= (c << 3);

                        s.bitb = b; s.bitk = k;
                        z.AvailableBytesIn = n; z.TotalBytesIn += p - z.NextIn; z.NextIn = p;
                        s.writeAt = q;

                        return ZlibConstants.Z_STREAM_END;
                    }
                    else
                    {
                        z.Message = "invalid literal/length code";

                        c = z.AvailableBytesIn - n; c = (k >> 3) < c ? k >> 3 : c; n += c; p -= c; k -= (c << 3);

                        s.bitb = b; s.bitk = k;
                        z.AvailableBytesIn = n; z.TotalBytesIn += p - z.NextIn; z.NextIn = p;
                        s.writeAt = q;

                        return ZlibConstants.Z_DATA_ERROR;
                    }
                }
                while (true);
            }
            while (m >= 258 && n >= 10);

            // not enough input or output--restore pointers and return
            c = z.AvailableBytesIn - n; c = (k >> 3) < c ? k >> 3 : c; n += c; p -= c; k -= (c << 3);

            s.bitb = b; s.bitk = k;
            z.AvailableBytesIn = n; z.TotalBytesIn += p - z.NextIn; z.NextIn = p;
            s.writeAt = q;

            return ZlibConstants.Z_OK;
        }
        internal int inflate_trees_dynamic(int nl, int nd, int[] c, int[] bl, int[] bd, int[] tl, int[] td, int[] hp, ZlibCodec z)
        {
            int result;

                        // build literal/length tree
                        initWorkArea(288);
                        hn[0] = 0;
                        result = huft_build(c, 0, nl, 257, cplens, cplext, tl, bl, hp, hn, v);
                        if (result != Z_OK || bl[0] == 0)
                        {
                                if (result == Z_DATA_ERROR)
                                {
                                        z.Message = "oversubscribed literal/length tree";
                                }
                                else if (result != Z_MEM_ERROR)
                                {
                                        z.Message = "incomplete literal/length tree";
                                        result = Z_DATA_ERROR;
                                }
                                return result;
                        }

                        // build distance tree
                        initWorkArea(288);
                        result = huft_build(c, nl, nd, 0, cpdist, cpdext, td, bd, hp, hn, v);

                        if (result != Z_OK || (bd[0] == 0 && nl > 257))
                        {
                                if (result == Z_DATA_ERROR)
                                {
                                        z.Message = "oversubscribed distance tree";
                                }
                                else if (result == Z_BUF_ERROR)
                                {
                                        z.Message = "incomplete distance tree";
                                        result = Z_DATA_ERROR;
                                }
                                else if (result != Z_MEM_ERROR)
                                {
                                        z.Message = "empty distance tree with lengths";
                                        result = Z_DATA_ERROR;
                                }
                                return result;
                        }

                        return Z_OK;
        }
        internal int inflate_trees_bits(int[] c, int[] bb, int[] tb, int[] hp, ZlibCodec z)
        {
            int result;
                        initWorkArea(19);
                        hn[0] = 0;
                        result = huft_build(c, 0, 19, 19, null, null, tb, bb, hp, hn, v);

                        if (result == Z_DATA_ERROR)
                        {
                                z.Message = "oversubscribed dynamic bit lengths tree";
                        }
                        else if (result == Z_BUF_ERROR || bb[0] == 0)
                        {
                                z.Message = "incomplete dynamic bit lengths tree";
                                result = Z_DATA_ERROR;
                        }
                        return result;
        }
 internal static int inflate_trees_fixed(int[] bl, int[] bd, int[][] tl, int[][] td, ZlibCodec z)
 {
     bl[0] = fixed_bl;
                 bd[0] = fixed_bd;
                 tl[0] = fixed_tl;
                 td[0] = fixed_td;
                 return Z_OK;
 }
 private void end()
 {
     if (z == null)
         return;
     if (_wantCompress)
     {
         _z.EndDeflate();
     }
     else
     {
         _z.EndInflate();
     }
     _z = null;
 }