C# Class ICSharpCode.SharpZipLib.Checksums.Crc32

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.

Inheritance: IChecksum

Show file Open project: NexusMods/NexusModManager-4.5 Class Usage Examples

Public Methods

Method	Description
Reset ( ) : void	Resets the CRC32 data checksum as if no update was ever called.
Update ( byte buffer ) : void	Updates the checksum with the bytes taken from the array.
Update ( byte buffer, int offset, int count ) : void	Adds the byte array to the data checksum.
Update ( int value ) : void	Updates the checksum with the int bval.

Method Details

Reset() public method

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

public Reset ( ) : void
return	void

Update() public method

Updates the checksum with the bytes taken from the array.

public Update ( byte buffer ) : void
buffer	byte	/// buffer an array of bytes ///
return	void

Update() public method

Adds the byte array to the data checksum.

public Update ( byte buffer, int offset, int count ) : void
buffer	byte	/// The buffer which contains the data ///
offset	int	/// The offset in the buffer where the data starts ///
count	int	/// The number of data bytes to update the CRC with. ///
return	void

Update() public method

Updates the checksum with the int bval.

public Update ( int value ) : void
value	int	/// the byte is taken as the lower 8 bits of value ///
return	void