CRC (coodex-utilities 0.2.3 API)

java.lang.Object
- org.coodex.util.CRC

```
public 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 and Description
`static class`	`CRC.Algorithm` Parameters represents set of parameters defining a particular CRC algorithm.
`static class`	`CRC.Parameters`

Constructor Summary

Constructors
Constructor and Description

CRC(CRC.Algorithm algorithm)
Constructs a new CRC processor for table based CRC calculations.

CRC(CRC.Parameters crcParams)

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

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`long`	`calculateCRC(byte[] data)` A convenience method allowing to calculate CRC in one call.
`static long`	`calculateCRC(CRC.Algorithm algorithm, byte[] data)`
`static long`	`calculateCRC(CRC.Algorithm algorithm, byte[] data, int offset, int length)`
`static long`	`calculateCRC(CRC.Parameters crcParams, byte[] data)`
`static long`	`calculateCRC(CRC.Parameters crcParams, byte[] data, int offset, int length)` This method implements simple straight forward bit by bit calculation.
`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
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - CRC
```
public CRC(CRC.Algorithm algorithm)
```
    Constructs a new CRC processor for table based CRC calculations. Underneath, it just calls finalCRC() method.
    
    Parameters:
    
    algorithm - CRC algorithm parameters
    
    Throws:
    
    RuntimeException - if CRC sum width is not divisible by 8
  - CRC
```
public CRC(CRC.Parameters crcParams)
```
- Method Detail
  - calculateCRC
```
public static long calculateCRC(CRC.Algorithm algorithm,
                                byte[] data)
```
  - calculateCRC
```
public static long calculateCRC(CRC.Algorithm algorithm,
                                byte[] data,
                                int offset,
                                int length)
```
  - calculateCRC
```
public static long calculateCRC(CRC.Parameters crcParams,
                                byte[] data)
```
  - calculateCRC
```
public static long calculateCRC(CRC.Parameters crcParams,
                                byte[] data,
                                int offset,
                                int length)
```
    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
  - 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
  - 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

Class CRC

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

CRC

CRC

Method Detail

calculateCRC

calculateCRC

calculateCRC

calculateCRC

init

update

update

finalCRC

calculateCRC

finalCRC8

finalCRC16

finalCRC32