188 lines
6.8 KiB
C#
188 lines
6.8 KiB
C#
using System;
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namespace ICSharpCode.SharpZipLib.Checksum
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{
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/// <summary>
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/// CRC-32 with unreversed data and reversed output
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/// </summary>
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/// <remarks>
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/// Generate a table for a byte-wise 32-bit CRC calculation on the polynomial:
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/// 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+x^0.
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///
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/// Polynomials over GF(2) are represented in binary, one bit per coefficient,
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/// with the lowest powers in the most significant bit. Then adding polynomials
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/// is just exclusive-or, and multiplying a polynomial by x is a right shift by
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/// one. If we call the above polynomial p, and represent a byte as the
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/// polynomial q, also with the lowest power in the most significant bit (so the
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/// byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
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/// where a mod b means the remainder after dividing a by b.
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///
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/// This calculation is done using the shift-register method of multiplying and
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/// taking the remainder. The register is initialized to zero, and for each
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/// incoming bit, x^32 is added mod p to the register if the bit is a one (where
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/// x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
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/// x (which is shifting right by one and adding x^32 mod p if the bit shifted
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/// out is a one). We start with the highest power (least significant bit) of
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/// q and repeat for all eight bits of q.
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///
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/// The table is simply the CRC of all possible eight bit values. This is all
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/// the information needed to generate CRC's on data a byte at a time for all
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/// combinations of CRC register values and incoming bytes.
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/// </remarks>
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public sealed class BZip2Crc : IChecksum
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{
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#region Instance Fields
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private const uint crcInit = 0xFFFFFFFF;
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//const uint crcXor = 0x00000000;
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private static readonly uint[] crcTable = {
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0X00000000, 0X04C11DB7, 0X09823B6E, 0X0D4326D9,
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0X130476DC, 0X17C56B6B, 0X1A864DB2, 0X1E475005,
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0X2608EDB8, 0X22C9F00F, 0X2F8AD6D6, 0X2B4BCB61,
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0X350C9B64, 0X31CD86D3, 0X3C8EA00A, 0X384FBDBD,
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0X4C11DB70, 0X48D0C6C7, 0X4593E01E, 0X4152FDA9,
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0X5F15ADAC, 0X5BD4B01B, 0X569796C2, 0X52568B75,
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0X6A1936C8, 0X6ED82B7F, 0X639B0DA6, 0X675A1011,
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0X791D4014, 0X7DDC5DA3, 0X709F7B7A, 0X745E66CD,
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0X9823B6E0, 0X9CE2AB57, 0X91A18D8E, 0X95609039,
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0X8B27C03C, 0X8FE6DD8B, 0X82A5FB52, 0X8664E6E5,
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0XBE2B5B58, 0XBAEA46EF, 0XB7A96036, 0XB3687D81,
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0XAD2F2D84, 0XA9EE3033, 0XA4AD16EA, 0XA06C0B5D,
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0XD4326D90, 0XD0F37027, 0XDDB056FE, 0XD9714B49,
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0XC7361B4C, 0XC3F706FB, 0XCEB42022, 0XCA753D95,
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0XF23A8028, 0XF6FB9D9F, 0XFBB8BB46, 0XFF79A6F1,
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0XE13EF6F4, 0XE5FFEB43, 0XE8BCCD9A, 0XEC7DD02D,
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0X34867077, 0X30476DC0, 0X3D044B19, 0X39C556AE,
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0X278206AB, 0X23431B1C, 0X2E003DC5, 0X2AC12072,
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0X128E9DCF, 0X164F8078, 0X1B0CA6A1, 0X1FCDBB16,
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0X018AEB13, 0X054BF6A4, 0X0808D07D, 0X0CC9CDCA,
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0X7897AB07, 0X7C56B6B0, 0X71159069, 0X75D48DDE,
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0X6B93DDDB, 0X6F52C06C, 0X6211E6B5, 0X66D0FB02,
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0X5E9F46BF, 0X5A5E5B08, 0X571D7DD1, 0X53DC6066,
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0X4D9B3063, 0X495A2DD4, 0X44190B0D, 0X40D816BA,
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0XACA5C697, 0XA864DB20, 0XA527FDF9, 0XA1E6E04E,
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0XBFA1B04B, 0XBB60ADFC, 0XB6238B25, 0XB2E29692,
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0X8AAD2B2F, 0X8E6C3698, 0X832F1041, 0X87EE0DF6,
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0X99A95DF3, 0X9D684044, 0X902B669D, 0X94EA7B2A,
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0XE0B41DE7, 0XE4750050, 0XE9362689, 0XEDF73B3E,
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0XF3B06B3B, 0XF771768C, 0XFA325055, 0XFEF34DE2,
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0XC6BCF05F, 0XC27DEDE8, 0XCF3ECB31, 0XCBFFD686,
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0XD5B88683, 0XD1799B34, 0XDC3ABDED, 0XD8FBA05A,
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0X690CE0EE, 0X6DCDFD59, 0X608EDB80, 0X644FC637,
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0X7A089632, 0X7EC98B85, 0X738AAD5C, 0X774BB0EB,
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0X4F040D56, 0X4BC510E1, 0X46863638, 0X42472B8F,
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0X5C007B8A, 0X58C1663D, 0X558240E4, 0X51435D53,
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0X251D3B9E, 0X21DC2629, 0X2C9F00F0, 0X285E1D47,
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0X36194D42, 0X32D850F5, 0X3F9B762C, 0X3B5A6B9B,
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0X0315D626, 0X07D4CB91, 0X0A97ED48, 0X0E56F0FF,
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0X1011A0FA, 0X14D0BD4D, 0X19939B94, 0X1D528623,
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0XF12F560E, 0XF5EE4BB9, 0XF8AD6D60, 0XFC6C70D7,
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0XE22B20D2, 0XE6EA3D65, 0XEBA91BBC, 0XEF68060B,
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0XD727BBB6, 0XD3E6A601, 0XDEA580D8, 0XDA649D6F,
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0XC423CD6A, 0XC0E2D0DD, 0XCDA1F604, 0XC960EBB3,
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0XBD3E8D7E, 0XB9FF90C9, 0XB4BCB610, 0XB07DABA7,
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0XAE3AFBA2, 0XAAFBE615, 0XA7B8C0CC, 0XA379DD7B,
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0X9B3660C6, 0X9FF77D71, 0X92B45BA8, 0X9675461F,
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0X8832161A, 0X8CF30BAD, 0X81B02D74, 0X857130C3,
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0X5D8A9099, 0X594B8D2E, 0X5408ABF7, 0X50C9B640,
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0X4E8EE645, 0X4A4FFBF2, 0X470CDD2B, 0X43CDC09C,
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0X7B827D21, 0X7F436096, 0X7200464F, 0X76C15BF8,
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0X68860BFD, 0X6C47164A, 0X61043093, 0X65C52D24,
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0X119B4BE9, 0X155A565E, 0X18197087, 0X1CD86D30,
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0X029F3D35, 0X065E2082, 0X0B1D065B, 0X0FDC1BEC,
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0X3793A651, 0X3352BBE6, 0X3E119D3F, 0X3AD08088,
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0X2497D08D, 0X2056CD3A, 0X2D15EBE3, 0X29D4F654,
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0XC5A92679, 0XC1683BCE, 0XCC2B1D17, 0XC8EA00A0,
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0XD6AD50A5, 0XD26C4D12, 0XDF2F6BCB, 0XDBEE767C,
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0XE3A1CBC1, 0XE760D676, 0XEA23F0AF, 0XEEE2ED18,
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0XF0A5BD1D, 0XF464A0AA, 0XF9278673, 0XFDE69BC4,
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0X89B8FD09, 0X8D79E0BE, 0X803AC667, 0X84FBDBD0,
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0X9ABC8BD5, 0X9E7D9662, 0X933EB0BB, 0X97FFAD0C,
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0XAFB010B1, 0XAB710D06, 0XA6322BDF, 0XA2F33668,
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0XBCB4666D, 0XB8757BDA, 0XB5365D03, 0XB1F740B4
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};
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/// <summary>
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/// The CRC data checksum so far.
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/// </summary>
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private uint checkValue;
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#endregion Instance Fields
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/// <summary>
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/// Initialise a default instance of <see cref="BZip2Crc"></see>
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/// </summary>
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public BZip2Crc()
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{
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Reset();
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}
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/// <summary>
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/// Resets the CRC data checksum as if no update was ever called.
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/// </summary>
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public void Reset()
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{
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checkValue = crcInit;
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}
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/// <summary>
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/// Returns the CRC data checksum computed so far.
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/// </summary>
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/// <remarks>Reversed Out = true</remarks>
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public long Value
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{
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get
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{
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// Tehcnically, the output should be:
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//return (long)(~checkValue ^ crcXor);
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// but x ^ 0 = x, so there is no point in adding
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// the XOR operation
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return (long)(~checkValue);
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}
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}
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/// <summary>
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/// Updates the checksum with the int bval.
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/// </summary>
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/// <param name = "bval">
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/// the byte is taken as the lower 8 bits of bval
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/// </param>
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/// <remarks>Reversed Data = false</remarks>
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public void Update(int bval)
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{
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checkValue = unchecked(crcTable[(byte)(((checkValue >> 24) & 0xFF) ^ bval)] ^ (checkValue << 8));
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}
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/// <summary>
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/// Updates the CRC data checksum with the bytes taken from
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/// a block of data.
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/// </summary>
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/// <param name="buffer">Contains the data to update the CRC with.</param>
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public void Update(byte[] buffer)
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{
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if (buffer == null)
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{
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throw new ArgumentNullException(nameof(buffer));
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}
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Update(new ArraySegment<byte>(buffer, 0, buffer.Length));
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}
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/// <summary>
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/// Update CRC data checksum based on a portion of a block of data
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/// </summary>
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/// <param name = "segment">
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/// The chunk of data to add
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/// </param>
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public void Update(ArraySegment<byte> segment)
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{
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var count = segment.Count;
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var offset = segment.Offset;
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while (--count >= 0)
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Update(segment.Array[offset++]);
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}
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}
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}
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