Package com.prineside.tdi2.utils

Class CRC

java.lang.Object
com.prineside.tdi2.utils.CRC
public final class CRC extends Object
This class provides utility functions for CRC calculation using either canonical straight forward approach or using "fast" table-driven implementation. Note, that even though table-driven implementation is much faster for processing large amounts of data and is commonly referred as fast algorithm, sometimes it might be quicker to calculate CRC using canonical algorithm then to prepare the table for table-driven implementation.

Using src is easy. Here is an example of calculating CCITT crc in one call using canonical approach. 

 
 String data = "123456789";
 long ccittCrc = CRC.calculateCRC(CRC.Parameters.CCITT, data.getBytes());
 System.out.printf("CRC is 0x%04X\n", ccittCrc); // prints "CRC is 0x29B1"

For larger data, table driven implementation is faster. Here is how to use it. 

 
 String data = "123456789";
 CRC tableDriven = new CRC(CRC.Parameters.XMODEM);
 long xmodemCrc = tableDriven.calculateCRC(data.getBytes());
 System.out.printf("CRC is 0x%04X\n", xmodemCrc); // prints "CRC is 0x31C3"

You can also reuse CRC object instance for another crc calculation.

Given that the only state for a CRC calculation is the "intermediate value" and it is stored in your code, you can even use same CRC instance to calculate CRC of multiple data sets in parallel. And if data is too big, you may feed it in chunks 

 
 long curValue = tableDriven.init(); // initialize intermediate value
 curValue = tableDriven.update(curValue, "123456789".getBytes()); // feed first chunk
 curValue = tableDriven.update(curValue, "01234567890".getBytes()); // feed next chunk
 long xmodemCrc2 = tableDriven.finalCRC(curValue); // gets CRC of whole data ("12345678901234567890")
 System.out.printf("CRC is 0x%04X\n", xmodemCrc2); // prints "CRC is 0x2C89"

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    static final class 
    CRC.Parameters
    Parameters represents set of parameters defining a particular CRC algorithm.

  • Constructor Summary

    Constructors
    Constructor
    Description
    CRC(CRC.Parameters crcParams)
    Constructs a new CRC processor for table based CRC calculations.

  • Method Summary

    Modifier and Type
    Method
    Description
    long
    calculateCRC(byte[] data)
    A convenience method allowing to calculate CRC in one call.
    long
    calculateCRC(byte[] data, int offset, int length)
     
    static long
    calculateCRC(CRC.Parameters crcParams, byte[] data)
    This method implements simple straight forward bit by bit calculation.
    static long
    calculateCRC(CRC.Parameters crcParams, byte[] data, int offset, int length)
     
    long
    finalCRC(long curValue)
    This method should be called to retrieve actual CRC for the data processed so far.
    short
    finalCRC16(long curValue)
    Is a convenience method to spare end users from explicit type conversion every time this package is used.
    int
    finalCRC32(long curValue)
    Is a convenience method to spare end users from explicit type conversion every time this package is used.
    byte
    finalCRC8(long curValue)
    Is a convenience method to spare end users from explicit type conversion every time this package is used.
    long
    init()
    Returns initial value for this CRC intermediate value This method is used when starting a new iterative CRC calculation (using init, update and finalCRC methods, possibly supplying data in chunks).
    long
    update(long curValue, byte[] chunk)
    A convenience method for feeding a complete byte array of data.
    long
    update(long curValue, byte[] chunk, int offset, int length)
    This method is used to feed data when performing iterative CRC calculation (using init, update and finalCRC methods, possibly supplying data in chunks).

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • CRC

      public CRC(CRC.Parameters crcParams)
      Constructs a new CRC processor for table based CRC calculations. Underneath, it just calls finalCRC() method.
      Parameters:
      crcParams - CRC algorithm parameters
      Throws:
      RuntimeException - if CRC sum width is not divisible by 8

  • Method Details

    • calculateCRC

      public static long calculateCRC(CRC.Parameters crcParams, byte[] data)
      This method implements simple straight forward bit by bit calculation. It is relatively slow for large amounts of data, but does not require any preparation steps. As a result, it might be faster in some cases then building a table required for faster calculation. Note: this implementation follows section 8 ("A Straightforward CRC Implementation") of Ross N. Williams paper as even though final/sample implementation of this algorithm provided near the end of that paper (and followed by most other implementations) is a bit faster, it does not work for polynomials shorter then 8 bits.
      Parameters:
      crcParams - CRC algorithm parameters
      data - data for the CRC calculation
      Returns:
      the CRC value of the data provided

    • calculateCRC

      public static long calculateCRC(CRC.Parameters crcParams, byte[] data, int offset, int length)

    • init

      public long init()
      Returns initial value for this CRC intermediate value This method is used when starting a new iterative CRC calculation (using init, update and finalCRC methods, possibly supplying data in chunks).
      Returns:
      initial value for this CRC intermediate value

    • update

      public long update(long curValue, byte[] chunk, int offset, int length)
      This method is used to feed data when performing iterative CRC calculation (using init, update and finalCRC methods, possibly supplying data in chunks). It can be called multiple times per CRC calculation to feed data to be processed in chunks.
      Parameters:
      curValue - CRC intermediate value so far
      chunk - data chunk to b processed by this call
      offset - is 0-based offset of the data to be processed in the array supplied
      length - indicates number of bytes to be processed.
      Returns:
      updated intermediate value for this CRC

    • update

      public long update(long curValue, byte[] chunk)
      A convenience method for feeding a complete byte array of data.
      Parameters:
      curValue - CRC intermediate value so far
      chunk - data chunk to b processed by this call
      Returns:
      updated intermediate value for this CRC

    • finalCRC

      public long finalCRC(long curValue)
      This method should be called to retrieve actual CRC for the data processed so far.
      Parameters:
      curValue - CRC intermediate value so far
      Returns:
      calculated CRC

    • calculateCRC

      public long calculateCRC(byte[] data)
      A convenience method allowing to calculate CRC in one call.
      Parameters:
      data - is data to calculate CRC on
      Returns:
      calculated CRC

    • calculateCRC

      public long calculateCRC(byte[] data, int offset, int length)

    • finalCRC8

      public byte finalCRC8(long curValue)
      Is a convenience method to spare end users from explicit type conversion every time this package is used. Underneath, it just calls finalCRC() method.
      Parameters:
      curValue - current intermediate crc state value
      Returns:
      the final CRC value
      Throws:
      RuntimeException - if crc being calculated is not 8-bit

    • finalCRC16

      public short finalCRC16(long curValue)
      Is a convenience method to spare end users from explicit type conversion every time this package is used. Underneath, it just calls finalCRC() method.
      Parameters:
      curValue - current intermediate crc state value
      Returns:
      the final CRC value
      Throws:
      RuntimeException - if crc being calculated is not 16-bit

    • finalCRC32

      public int finalCRC32(long curValue)
      Is a convenience method to spare end users from explicit type conversion every time this package is used. Underneath, it just calls finalCRC() method.
      Parameters:
      curValue - current intermediate crc state value
      Returns:
      the final CRC value
      Throws:
      RuntimeException - if crc being calculated is not 32-bit