#### /Utilities/Compression/Checksums/Crc32.cs

#
C# | 298 lines | 176 code | 31 blank | 91 comment | 7 complexity | 761ea8406bed06a46eff72c34bc6b6e1 MD5 | raw file
``````
using System;

using System.IO;

namespace Delta.Utilities.Compression.Checksums

{

/// <summary>

/// Crc32 - Computes CRC32 data checksum of a data stream. 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'str on data a byte at a time for

/// all combinations of CRC register values and incoming bytes.

/// </summary>

public sealed class Crc32

{

#region Constants

/// <summary>

/// Crc seed

/// </summary>

private const uint CrcSeed = 0xFFFFFFFF;

/// <summary>

/// Crc table

/// </summary>

/// <returns>Uint []</returns>

private static readonly uint[] CrcTable = new uint[]

{

0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419,

0x706AF48F, 0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4,

0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07,

0x90BF1D91, 0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE,

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,

0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA, 0xBE0B1010,

0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,

0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17,

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,

0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,

0xCDD70693, 0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8,

0x5D681B02, 0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B,

0x2D02EF8D

};

#endregion

#region ComputeCrcValue (Static)

/// <summary>

/// Compute crc value

/// </summary>

/// <param name="buffer">Buffer</param>

/// <returns>Long</returns>

public static long ComputeCrcValue(byte[] buffer)

{

Crc32 crc = new Crc32();

crc.Update(buffer);

return crc.Value;

}

// ComputeCrcValue(buffer)

/// <summary>

/// Compute crc value

/// </summary>

/// <param name="stream">Stream</param>

/// <returns>Long</returns>

public static long ComputeCrcValue(Stream stream)

{

// Make sure the stream is good to go.

stream.CanSeek == false)

{

throw new NotSupportedException(

"Can't calculated checksum of a stream that does not support " +

}

// Remember old stream position

long oldPosition = stream.Position;

// Get all data

byte[] buffer = new byte[stream.Length];

stream.Seek(0, SeekOrigin.Begin);

// Restore old position

stream.Position = oldPosition;

// Compute and return checksum

return ComputeCrcValue(buffer);

}

#endregion

#region Value (Public)

/// <summary>

/// Returns the CRC32 data checksum computed so far.

/// </summary>

public long Value

{

get

{

return crc;

} // get

set

{

crc = (uint)value;

} // set

}

#endregion

#region Private

#region crc (Private)

/// <summary>

/// The crc data checksum so far.

/// </summary>

private uint crc;

#endregion

#endregion

#region Reset (Public)

/// <summary>

/// Resets the CRC32 data checksum as if no update was ever called.

/// </summary>

public void Reset()

{

crc = 0;

}

#endregion

#region Update (Public)

/// <summary>

/// Updates the checksum with the int value.

/// </summary>

/// <param name="value">Byte is taken as the lower 8 bits of value</param>

public void Update(int value)

{

crc ^= CrcSeed;

crc = CrcTable[(crc ^ value) & 0xFF] ^ (crc >> 8);

crc ^= CrcSeed;

}

// Update(value)

/// <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);

}

// Update(buffer)

/// <summary>

/// Adds the byte array to the data checksum.

/// </summary>

/// <param name="buffer">Buffer which contains the data</param>

/// <param name="offset">Offset in the buffer where the data starts</param>

/// <param name="count">Length of the data</param>

public void Update(byte[] buffer, int offset, int count)

{

if (buffer == null)

{

throw new ArgumentNullException("buffer");

} // if (buf)

if (offset < 0 ||

count < 0 ||

offset + count > buffer.Length)

{

throw new ArgumentOutOfRangeException();

} // if (off)

crc ^= CrcSeed;

while (--count >= 0)

{

crc = CrcTable[(crc ^ buffer[offset++]) & 0xFF] ^ (crc >> 8);

} // while (--len)

crc ^= CrcSeed;

}

#endregion

#region Methods (Private)

#region ComputeCrc32

/// <summary>

/// Compute crc 32

/// </summary>

/// <param name="oldCrc">Old crc</param>

/// <param name="value">Value</param>

/// <returns>Uint</returns>

internal static uint ComputeCrc32(uint oldCrc, byte value)

{

return (CrcTable[(oldCrc ^ value) & 0xFF] ^ (oldCrc >> 8));

}

#endregion

#endregion

/// <summary>

/// Crc 32 tests

/// </summary>

private class Crc32Tests

{

#region Helpers

#region TestCrc32

/// <summary>

/// Test crc 32

/// </summary>

public void TestCrc32()

{

Crc32 testCrc = new Crc32();

// Test assigning and clearing

testCrc.Value = 100;

Assert.Equal(100, testCrc.Value);

testCrc.Reset();

Assert.Equal(0, testCrc.Value);

// Throw in a byte array

byte[] someData = new byte[]

{

59, 49, 193, 98, 4, 199, 254, 9, 42

};

testCrc.Update(someData);

Assert.Equal(2271575830, testCrc.Value);

// Also test static methods

Assert.Equal(1131014251L, ComputeCrc32(65953, 201));

Assert.Equal(2271575830L, ComputeCrcValue(someData));

}

#endregion

#endregion

}

}

}

``````