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[Dotgnu-pnet-commits] pnetlib/SharpZipLib/Checksums Adler32.cs, NONE, 1


From: Rhys Weatherley <address@hidden>
Subject: [Dotgnu-pnet-commits] pnetlib/SharpZipLib/Checksums Adler32.cs, NONE, 1.1 CRC32.cs, NONE, 1.1 IChecksum.cs, NONE, 1.1 StrangeCRC.cs, NONE, 1.1
Date: Wed, 08 Oct 2003 07:37:06 +0000

Update of /cvsroot/dotgnu-pnet/pnetlib/SharpZipLib/Checksums
In directory subversions:/tmp/cvs-serv5756/SharpZipLib/Checksums

Added Files:
        Adler32.cs CRC32.cs IChecksum.cs StrangeCRC.cs 
Log Message:


Add the "SharpZipLib" directory to pnetlib, which is a port of
SharpDevelop's compression handling library.


--- NEW FILE: Adler32.cs ---
// Adler32.cs - Computes Adler32 data checksum of a data stream
// Copyright (C) 2001 Mike Krueger
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

using System;

namespace ICSharpCode.SharpZipLib.Checksums 
{
        
        /// <summary>
        /// Computes Adler32 checksum for a stream of data. An Adler32
        /// checksum is not as reliable as a CRC32 checksum, but a lot faster to
        /// compute.
        /// 
        /// The specification for Adler32 may be found in RFC 1950.
        /// ZLIB Compressed Data Format Specification version 3.3)
        /// 
        /// 
        /// From that document:
        /// 
        ///      "ADLER32 (Adler-32 checksum)
        ///       This contains a checksum value of the uncompressed data
        ///       (excluding any dictionary data) computed according to Adler-32
        ///       algorithm. This algorithm is a 32-bit extension and 
improvement
        ///       of the Fletcher algorithm, used in the ITU-T X.224 / ISO 8073
        ///       standard.
        /// 
        ///       Adler-32 is composed of two sums accumulated per byte: s1 is
        ///       the sum of all bytes, s2 is the sum of all s1 values. Both 
sums
        ///       are done modulo 65521. s1 is initialized to 1, s2 to zero.  
The
        ///       Adler-32 checksum is stored as s2*65536 + s1 in most-
        ///       significant-byte first (network) order."
        /// 
        ///  "8.2. The Adler-32 algorithm
        /// 
        ///    The Adler-32 algorithm is much faster than the CRC32 algorithm 
yet
        ///    still provides an extremely low probability of undetected errors.
        /// 
        ///    The modulo on unsigned long accumulators can be delayed for 5552
        ///    bytes, so the modulo operation time is negligible.  If the bytes
        ///    are a, b, c, the second sum is 3a + 2b + c + 3, and so is 
position
        ///    and order sensitive, unlike the first sum, which is just a
        ///    checksum.  That 65521 is prime is important to avoid a possible
        ///    large class of two-byte errors that leave the check unchanged.
        ///    (The Fletcher checksum uses 255, which is not prime and which 
also
        ///    makes the Fletcher check insensitive to single byte changes 0 -
        ///    255.)
        /// 
        ///    The sum s1 is initialized to 1 instead of zero to make the length
        ///    of the sequence part of s2, so that the length does not have to 
be
        ///    checked separately. (Any sequence of zeroes has a Fletcher
        ///    checksum of zero.)"
        /// </summary>
        /// <see 
cref="ICSharpCode.SharpZipLib.Zip.Compression.Streams.InflaterInputStream"/>
        /// <see 
cref="ICSharpCode.SharpZipLib.Zip.Compression.Streams.DeflaterOutputStream"/>
        public sealed class Adler32 : IChecksum
        {
                /// <summary>
                /// largest prime smaller than 65536
                /// </summary>
                readonly static uint BASE = 65521;
                
                uint checksum;
                
                /// <summary>
                /// Returns the Adler32 data checksum computed so far.
                /// </summary>
                public long Value 
                {
                        get 
                        {
                                return checksum;
                        }
                }
                
                /// <summary>
                /// Creates a new instance of the <code>Adler32</code> class.
                /// The checksum starts off with a value of 1.
                /// </summary>
                public Adler32()
                {
                        Reset();
                }
                
                /// <summary>
                /// Resets the Adler32 checksum to the initial value.
                /// </summary>
                public void Reset()
                {
                        checksum = 1; //Initialize to 1
                }
                
                /// <summary>
                /// Updates the checksum with the byte b.
                /// </summary>
                /// <param name="bval">
                /// the data value to add. The high byte of the int is ignored.
                /// </param>
                public void Update(int bval)
                {
                        //We could make a length 1 byte array and call update 
again, but I
                        //would rather not have that overhead
                        uint s1 = checksum & 0xFFFF;
                        uint s2 = checksum >> 16;
                        
                        s1 = (s1 + ((uint)bval & 0xFF)) % BASE;
                        s2 = (s1 + s2) % BASE;
                        
                        checksum = (s2 << 16) + s1;
                }
                
                /// <summary>
                /// Updates the checksum with the bytes taken from the array.
                /// </summary>
                /// <param name="buffer">
                /// buffer an array of bytes
                /// </param>
                public void Update(byte[] buffer)
                {
                        Update(buffer, 0, buffer.Length);
                }
                
                /// <summary>
                /// Updates the checksum with the bytes taken from the array.
                /// </summary>
                /// <param name="buf">
                /// an array of bytes
                /// </param>
                /// <param name="off">
                /// the start of the data used for this update
                /// </param>
                /// <param name="len">
                /// the number of bytes to use for this update
                /// </param>
                public void Update(byte[] buf, int off, int len)
                {
                        if (buf == null) 
                        {
                                throw new ArgumentNullException("buf");
                        }
                        
                        if (off < 0 || len < 0 || off + len > buf.Length) 
                        {
                                throw new ArgumentOutOfRangeException();
                        }
                        
                        //(By Per Bothner)
                        uint s1 = checksum & 0xFFFF;
                        uint s2 = checksum >> 16;
                        
                        while (len > 0) 
                        {
                                // We can defer the modulo operation:
                                // s1 maximally grows from 65521 to 65521 + 255 
* 3800
                                // s2 maximally grows by 3800 * median(s1) = 
2090079800 < 2^31
                                int n = 3800;
                                if (n > len) 
                                {
                                        n = len;
                                }
                                len -= n;
                                while (--n >= 0) 
                                {
                                        s1 = s1 + (uint)(buf[off++] & 0xFF);
                                        s2 = s2 + s1;
                                }
                                s1 %= BASE;
                                s2 %= BASE;
                        }
                        
                        checksum = (s2 << 16) | s1;
                }
        }
}

--- NEW FILE: IChecksum.cs ---
// IChecksum.cs - Interface to compute a data checksum
// Copyright (C) 2001 Mike Krueger
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

namespace ICSharpCode.SharpZipLib.Checksums 
{
        
        /// <summary>
        /// Interface to compute a data checksum used by checked input/output 
streams.
        /// A data checksum can be updated by one byte or with a byte array. 
After each
        /// update the value of the current checksum can be returned by calling
        /// <code>getValue</code>. The complete checksum object can also be 
reset
        /// so it can be used again with new data.
        /// </summary>
        public interface IChecksum
        {
                /// <summary>
                /// Returns the data checksum computed so far.
                /// </summary>
                long Value 
                {
                        get;
                }
                
                /// <summary>
                /// Resets the data checksum as if no update was ever called.
                /// </summary>
                void Reset();
                
                /// <summary>
                /// Adds one byte to the data checksum.
                /// </summary>
                /// <param name = "bval">
                /// the data value to add. The high byte of the int is ignored.
                /// </param>
                void Update(int bval);
                
                /// <summary>
                /// Updates the data checksum with the bytes taken from the 
array.
                /// </summary>
                /// <param name="buffer">
                /// buffer an array of bytes
                /// </param>
                void Update(byte[] buffer);
                
                /// <summary>
                /// Adds the byte array to the data checksum.
                /// </summary>
                /// <param name = "buf">
                /// the buffer which contains the data
                /// </param>
                /// <param name = "off">
                /// the offset in the buffer where the data starts
                /// </param>
                /// <param name = "len">
                /// the length of the data
                /// </param>
                void Update(byte[] buf, int off, int len);
        }
}

--- NEW FILE: StrangeCRC.cs ---
// StrangeCRC.cs - computes a crc used in the bziplib ... I don't think that
//                 this is the 'standard' crc, please correct me, if I'm wrong
// Copyright (C) 2001 Mike Krueger
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

using System;

namespace ICSharpCode.SharpZipLib.Checksums 
{
        
        public class StrangeCRC : IChecksum
        {
                readonly static uint[] crc32Table = {
                                                                                
                0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9,
                                                                                
                0x130476dc, 0x17c56b6b, 0x1a864db2, 0x1e475005,
                                                                                
                0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61,
                                                                                
                0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd,
                                                                                
                0x4c11db70, 0x48d0c6c7, 0x4593e01e, 0x4152fda9,
                                                                                
                0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75,
                                                                                
                0x6a1936c8, 0x6ed82b7f, 0x639b0da6, 0x675a1011,
                                                                                
                0x791d4014, 0x7ddc5da3, 0x709f7b7a, 0x745e66cd,
                                                                                
                0x9823b6e0, 0x9ce2ab57, 0x91a18d8e, 0x95609039,
                                                                                
                0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5,
                                                                                
                0xbe2b5b58, 0xbaea46ef, 0xb7a96036, 0xb3687d81,
                                                                                
                0xad2f2d84, 0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d,
                                                                                
                0xd4326d90, 0xd0f37027, 0xddb056fe, 0xd9714b49,
                                                                                
                0xc7361b4c, 0xc3f706fb, 0xceb42022, 0xca753d95,
                                                                                
                0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1,
                                                                                
                0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d,
                                                                                
                0x34867077, 0x30476dc0, 0x3d044b19, 0x39c556ae,
                                                                                
                0x278206ab, 0x23431b1c, 0x2e003dc5, 0x2ac12072,
                                                                                
                0x128e9dcf, 0x164f8078, 0x1b0ca6a1, 0x1fcdbb16,
                                                                                
                0x018aeb13, 0x054bf6a4, 0x0808d07d, 0x0cc9cdca,
                                                                                
                0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde,
                                                                                
                0x6b93dddb, 0x6f52c06c, 0x6211e6b5, 0x66d0fb02,
                                                                                
                0x5e9f46bf, 0x5a5e5b08, 0x571d7dd1, 0x53dc6066,
                                                                                
                0x4d9b3063, 0x495a2dd4, 0x44190b0d, 0x40d816ba,
                                                                                
                0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e,
                                                                                
                0xbfa1b04b, 0xbb60adfc, 0xb6238b25, 0xb2e29692,
                                                                                
                0x8aad2b2f, 0x8e6c3698, 0x832f1041, 0x87ee0df6,
                                                                                
                0x99a95df3, 0x9d684044, 0x902b669d, 0x94ea7b2a,
                                                                                
                0xe0b41de7, 0xe4750050, 0xe9362689, 0xedf73b3e,
                                                                                
                0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
                                                                                
                0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686,
                                                                                
                0xd5b88683, 0xd1799b34, 0xdc3abded, 0xd8fba05a,
                                                                                
                0x690ce0ee, 0x6dcdfd59, 0x608edb80, 0x644fc637,
                                                                                
                0x7a089632, 0x7ec98b85, 0x738aad5c, 0x774bb0eb,
                                                                                
                0x4f040d56, 0x4bc510e1, 0x46863638, 0x42472b8f,
                                                                                
                0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53,
                                                                                
                0x251d3b9e, 0x21dc2629, 0x2c9f00f0, 0x285e1d47,
                                                                                
                0x36194d42, 0x32d850f5, 0x3f9b762c, 0x3b5a6b9b,
                                                                                
                0x0315d626, 0x07d4cb91, 0x0a97ed48, 0x0e56f0ff,
                                                                                
                0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623,
                                                                                
                0xf12f560e, 0xf5ee4bb9, 0xf8ad6d60, 0xfc6c70d7,
                                                                                
                0xe22b20d2, 0xe6ea3d65, 0xeba91bbc, 0xef68060b,
                                                                                
                0xd727bbb6, 0xd3e6a601, 0xdea580d8, 0xda649d6f,
                                                                                
                0xc423cd6a, 0xc0e2d0dd, 0xcda1f604, 0xc960ebb3,
                                                                                
                0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7,
                                                                                
                0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b,
                                                                                
                0x9b3660c6, 0x9ff77d71, 0x92b45ba8, 0x9675461f,
                                                                                
                0x8832161a, 0x8cf30bad, 0x81b02d74, 0x857130c3,
                                                                                
                0x5d8a9099, 0x594b8d2e, 0x5408abf7, 0x50c9b640,
                                                                                
                0x4e8ee645, 0x4a4ffbf2, 0x470cdd2b, 0x43cdc09c,
                                                                                
                0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8,
                                                                                
                0x68860bfd, 0x6c47164a, 0x61043093, 0x65c52d24,
                                                                                
                0x119b4be9, 0x155a565e, 0x18197087, 0x1cd86d30,
                                                                                
                0x029f3d35, 0x065e2082, 0x0b1d065b, 0x0fdc1bec,
                                                                                
                0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088,
                                                                                
                0x2497d08d, 0x2056cd3a, 0x2d15ebe3, 0x29d4f654,
                                                                                
                0xc5a92679, 0xc1683bce, 0xcc2b1d17, 0xc8ea00a0,
                                                                                
                0xd6ad50a5, 0xd26c4d12, 0xdf2f6bcb, 0xdbee767c,
                                                                                
                0xe3a1cbc1, 0xe760d676, 0xea23f0af, 0xeee2ed18,
                                                                                
                0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
                                                                                
                0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0,
                                                                                
                0x9abc8bd5, 0x9e7d9662, 0x933eb0bb, 0x97ffad0c,
                                                                                
                0xafb010b1, 0xab710d06, 0xa6322bdf, 0xa2f33668,
                                                                                
                0xbcb4666d, 0xb8757bda, 0xb5365d03, 0xb1f740b4
                                                                                
        };
                int globalCrc;
        
                public StrangeCRC() 
                {
                        Reset();
                }
        
                public void Reset()
                {
                        globalCrc = -1;
                }
        
                public long Value 
                {
                        get 
                        {
                                return ~globalCrc;
                        }
                }
                
                public void Update(int inCh)
                {
                        int temp = (globalCrc >> 24) ^ inCh;
                        if (temp < 0) 
                        {
                                temp = 256 + temp;
                        }
                        globalCrc = (int)((globalCrc << 8) ^ crc32Table[temp]);
                }
                
                public void Update(byte[] buf)
                {
                        Update(buf, 0, buf.Length);
                }
                
                public void Update(byte[] buf, int off, int len)
                {
                        if (buf == null) 
                        {
                                throw new ArgumentNullException("buf");
                        }
                        
                        if (off < 0 || len < 0 || off + len > buf.Length) 
                        {
                                throw new ArgumentOutOfRangeException();
                        }
                        
                        for (int i = 0; i < len; ++i) 
                        {
                                Update(buf[off++]);
                        }
                }
        }
}

--- NEW FILE: CRC32.cs ---
// CRC32.cs - Computes CRC32 data checksum of a data stream
// Copyright (C) 2001 Mike Krueger
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

using System;

namespace ICSharpCode.SharpZipLib.Checksums 
{
        
        /// <summary>
        /// Generate a table for a byte-wise 32-bit CRC calculation on the 
polynomial:
        /// x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.
        ///
        /// Polynomials over GF(2) are represented in binary, one bit per 
coefficient,
        /// with the lowest powers in the most significant bit.  Then adding 
polynomials
        /// is just exclusive-or, and multiplying a polynomial by x is a right 
shift by
        /// one.  If we call the above polynomial p, and represent a byte as the
        /// polynomial q, also with the lowest power in the most significant 
bit (so the
        /// byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) 
mod p,
        /// where a mod b means the remainder after dividing a by b.
        ///
        /// This calculation is done using the shift-register method of 
multiplying and
        /// taking the remainder.  The register is initialized to zero, and for 
each
        /// incoming bit, x^32 is added mod p to the register if the bit is a 
one (where
        /// x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied 
mod p by
        /// x (which is shifting right by one and adding x^32 mod p if the bit 
shifted
        /// out is a one).  We start with the highest power (least significant 
bit) of
        /// q and repeat for all eight bits of q.
        ///
        /// The table is simply the CRC of all possible eight bit values.  This 
is all
        /// the information needed to generate CRC's on data a byte at a time 
for all
        /// combinations of CRC register values and incoming bytes.
        /// </summary>
        public sealed class Crc32 : IChecksum
        {
                readonly static uint CrcSeed = 0xFFFFFFFF;
                
                public readonly static uint[] CrcTable = new uint[] {
                         0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 
0x076DC419,
                         0x706AF48F, 0xE963A535, 0x9E6495A3, 0x0EDB8832, 
0x79DCB8A4,
                         0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 
0xE7B82D07,
                         0x90BF1D91, 0x1DB71064, 0x6AB020F2, 0xF3B97148, 
0x84BE41DE,
                         0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7, 
0x136C9856,
                         0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 
0x63066CD9,
                         0xFA0F3D63, 0x8D080DF5, 0x3B6E20C8, 0x4C69105E, 
0xD56041E4,
                         0xA2677172, 0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 
0xA50AB56B,
                         0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 
0x32D86CE3,
                         0x45DF5C75, 0xDCD60DCF, 0xABD13D59, 0x26D930AC, 
0x51DE003A,
                         0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, 
0xCFBA9599,
                         0xB8BDA50F, 0x2802B89E, 0x5F058808, 0xC60CD9B2, 
0xB10BE924,
                         0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D, 
0x76DC4190,
                         0x01DB7106, 0x98D220BC, 0xEFD5102A, 0x71B18589, 
0x06B6B51F,
                         0x9FBFE4A5, 0xE8B8D433, 0x7807C9A2, 0x0F00F934, 
0x9609A88E,
                         0xE10E9818, 0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 
0xE6635C01,
                         0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, 
0x6C0695ED,
                         0x1B01A57B, 0x8208F4C1, 0xF50FC457, 0x65B0D9C6, 
0x12B7E950,
                         0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 
0x8CD37CF3,
                         0xFBD44C65, 0x4DB26158, 0x3AB551CE, 0xA3BC0074, 
0xD4BB30E2,
                         0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB, 
0x4369E96A,
                         0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73, 
0x33031DE5,
                         0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA, 
0xBE0B1010,
                         0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 
0xCE61E49F,
                         0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 
0x59B33D17,
                         0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD, 0xEDB88320, 
0x9ABFB3B6,
                         0x03B6E20C, 0x74B1D29A, 0xEAD54739, 0x9DD277AF, 
0x04DB2615,
                         0x73DC1683, 0xE3630B12, 0x94643B84, 0x0D6D6A3E, 
0x7A6A5AA8,
                         0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1, 
0xF00F9344, 
                         0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 
0x806567CB,
                         0x196C3671, 0x6E6B06E7, 0xFED41B76, 0x89D32BE0, 
0x10DA7A5A,
                         0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 
0x60B08ED5,
                         0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 
0xD1BB67F1,
                         0xA6BC5767, 0x3FB506DD, 0x48B2364B, 0xD80D2BDA, 
0xAF0A1B4C,
                         0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55, 
0x316E8EEF,
                         0x4669BE79, 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 
0x5268E236,
                         0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F, 
0xC5BA3BBE,
                         0xB2BD0B28, 0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 
0xB5D0CF31,
                         0x2CD99E8B, 0x5BDEAE1D, 0x9B64C2B0, 0xEC63F226, 
0x756AA39C,
                         0x026D930A, 0x9C0906A9, 0xEB0E363F, 0x72076785, 
0x05005713,
                         0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 
0x92D28E9B,
                         0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21, 0x86D3D2D4, 
0xF1D4E242,
                         0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 
0x6FB077E1,
                         0x18B74777, 0x88085AE6, 0xFF0F6A70, 0x66063BCA, 
0x11010B5C,
                         0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45, 
0xA00AE278,
                         0xD70DD2EE, 0x4E048354, 0x3903B3C2, 0xA7672661, 
0xD06016F7,
                         0x4969474D, 0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC, 
0x40DF0B66,
                         0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 
0x30B5FFE9,
                         0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 
0xBAD03605,
                         0xCDD70693, 0x54DE5729, 0x23D967BF, 0xB3667A2E, 
0xC4614AB8,
                         0x5D681B02, 0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1, 
0x5A05DF1B, 
                         0x2D02EF8D
                };
                
                /// <summary>
                /// The crc data checksum so far.
                /// </summary>
                uint crc = 0;
                
                /// <summary>
                /// Returns the CRC32 data checksum computed so far.
                /// </summary>
                public long Value {
                        get {
                                return (long)crc;
                        }
                        set {
                                crc = (uint)value;
                        }
                }
                
                /// <summary>
                /// Resets the CRC32 data checksum as if no update was ever 
called.
                /// </summary>
                public void Reset() 
                { 
                        crc = 0; 
                }
                
                /// <summary>
                /// Updates the checksum with the int bval.
                /// </summary>
                /// <param name = "bval">
                /// the byte is taken as the lower 8 bits of bval
                /// </param>
                public void Update(int bval)
                {
                        crc ^= CrcSeed;
                        crc  = CrcTable[(crc ^ bval) & 0xFF] ^ (crc >> 8);
                        crc ^= CrcSeed;
                }
                
                /// <summary>
                /// Updates the checksum with the bytes taken from the array.
                /// </summary>
                /// <param name="buffer">
                /// buffer an array of bytes
                /// </param>
                public void Update(byte[] buffer)
                {
                        Update(buffer, 0, buffer.Length);
                }
                
                /// <summary>
                /// Adds the byte array to the data checksum.
                /// </summary>
                /// <param name = "buf">
                /// the buffer which contains the data
                /// </param>
                /// <param name = "off">
                /// the offset in the buffer where the data starts
                /// </param>
                /// <param name = "len">
                /// the length of the data
                /// </param>
                public void Update(byte[] buf, int off, int len)
                {
                        if (buf == null) {
                                throw new ArgumentNullException("buf");
                        }
                        
                        if (off < 0 || len < 0 || off + len > buf.Length) {
                                throw new ArgumentOutOfRangeException();
                        }
                        
                        crc ^= CrcSeed;
                        
                        while (--len >= 0) {
                                crc = CrcTable[(crc ^ buf[off++]) & 0xFF] ^ 
(crc >> 8);
                        }
                        
                        crc ^= CrcSeed;
                }
        }
}





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