Class Crc32

CRC-32 with reversed data and unreversed output

Inheritance
System.Object
Crc32
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 Crc32 : IChecksum
Remarks

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+x^0.

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.

Constructors

Crc32()

Initialise a default instance of Crc32

Declaration
public Crc32()

Properties

Value

Returns the CRC data checksum computed so far.

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

Implements
Remarks

Reversed Out = false

Methods

Reset()

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

Declaration
public void Reset()
Implements

Update(Byte[])

Updates the CRC 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 CRC with.
Implements

Update(Byte[], Int32, Int32)

Update CRC 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 int bval.

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

the byte is taken as the lower 8 bits of bval
Implements
Remarks

Reversed Data = true