C# Class ICSharpCode.SharpZipLib.Checksum.Adler32

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.)"
Inheritance: IChecksum
Exibir arquivo Open project: icsharpcode/SharpZipLib Class Usage Examples

Public Methods

Method Description
Adler32 ( ) : System

Initialise a default instance of

Reset ( ) : void

Resets the Adler32 data checksum as if no update was ever called.
Update ( byte buffer ) : void

Updates the Adler32 data checksum with the bytes taken from a block of data.
Update ( byte buffer, int offset, int count ) : void

Update Adler32 data checksum based on a portion of a block of data
Update ( int bval ) : void

Updates the checksum with the byte b.

Method Details

Adler32() public method

Initialise a default instance of
public Adler32 ( ) : System
return System

Reset() public method

Resets the Adler32 data checksum as if no update was ever called.
public Reset ( ) : void
return void

Update() public method

Updates the Adler32 data checksum with the bytes taken from a block of data.
public Update ( byte buffer ) : void
buffer byte Contains the data to update the checksum with.
return void

Update() public method

Update Adler32 data checksum based on a portion of a block of data
public Update ( byte buffer, int offset, int count ) : void
buffer byte Contains the data to update the CRC with.
offset int The offset into 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 byte b.
public Update ( int bval ) : void
bval int /// The data value to add. The high byte of the int is ignored. ///
return void