org.jscsi.parser.digest

Class CRCTables

java.lang.Object

org.jscsi.parser.digest.CRCTables

public final class CRCTables
extends Object

CRCTables

This class generates tables for CRC algorithm. It is possible to change the generator polynom and the offset. Usage:

1. Make new CRCTables object.
2. Put generatorPolynom in the constructor.
3. Invoke the method getTable with offset as an argument. The offset is an integer number, which specifies the number of bits to shift, e.g. for A offset is 56, for D 32.
4. You will have CRC table(0-255) for the requested polynom.

Author:

Stepan

Constructor Summary

Constructors

Constructor and Description
CRCTables(long initGeneratorPolynom) Constructor to create a new, empty CRCTables object with the initialized generator polynom.

Method Summary

Methods

Modifier and Type	Method and Description
protected int	calculateCRC32(long value) Method for CRC calculation for the just one value (type long) Algorithm: Load the register with zero bits.
int[]	getTable(int offset) Returns all remainders of the polynomial division for the given offset.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CRCTables

public CRCTables(long initGeneratorPolynom)

Constructor to create a new, empty CRCTables object with the initialized generator polynom.

Parameters:

initGeneratorPolynom - The generator polynom to use.

Method Detail

getTable

public final int[] getTable(int offset)

Returns all remainders of the polynomial division for the given offset.

Parameters:

offset - The numbers of bits to shift, e.g. for A offset is 56, for D 32.

Returns:

The CRC table with all remainders for the given offset.

calculateCRC32

protected final int calculateCRC32(long value)

Method for CRC calculation for the just one value (type long) Algorithm: Load the register with zero bits. Reverse message Augment the message by appending W zero bits to the end of it. While (more message bits) Begin Shift the register left by one bit, reading the next bit of the augmented message into register bit position 0. If (a 1 bit popped out of the register during step 3) Register = Register XOR Poly. End Reverse register The register now contains the CRC. Notes: W=32, that's why we have offsets 32, 40, 48 and 56 instead of 0,8,16,24 Size of register=W;

Parameters:

value - A long value, for which the CRC should be calculated.

Returns:

The remainder of the polynomial division --> CRC.