Class 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
System.Object
Adler32
Inherited Members
System.Object.ToString()
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
Namespace: System.Dynamic.ExpandoObject
Assembly: cs.temp.dll.dll
Syntax
public sealed class Adler32 : IChecksum

Constructors

Adler32()

Initialise a default instance of Adler32

Declaration
public Adler32()

Properties

Value

Returns the Adler32 data checksum computed so far.

Declaration
public long Value { get; }
Property Value
System.Int64

Implements

Methods

Reset()

Resets the Adler32 data checksum as if no update was ever called.

Declaration
public void Reset()
Implements

Update(Byte[])

Updates the Adler32 data checksum with the bytes taken from a block of data.

Declaration
public void Update(byte[] buffer)
Parameters
System.Byte[] buffer

Contains the data to update the checksum with.
Implements

Update(Byte[], Int32, Int32)

Update Adler32 data checksum based on a portion of a block of data

Declaration
public void Update(byte[] buffer, int offset, int count)
Parameters
System.Byte[] buffer

Contains the data to update the CRC with.
System.Int32 offset

The offset into the buffer where the data starts
System.Int32 count

The number of data bytes to update the CRC with.
Implements

Update(Int32)

Updates the checksum with the byte b.

Declaration
public void Update(int bval)
Parameters
System.Int32 bval

The data value to add. The high byte of the int is ignored.
Implements