CRC (coodex-utilities 0.5.0-RC1 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"
 
 
```

嵌套类概要

嵌套类
限定符和类型类和说明

static class CRC.Algorithm
Parameters represents set of parameters defining a particular CRC algorithm.

static class CRC.Parameters

嵌套类
限定符和类型	类和说明
`static class`	`CRC.Algorithm` Parameters represents set of parameters defining a particular CRC algorithm.
`static class`	`CRC.Parameters`

构造器概要

构造器
构造器和说明

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

CRC(CRC.Parameters crcParams)

构造器
构造器和说明
`CRC(CRC.Algorithm algorithm)` Constructs a new CRC processor for table based CRC calculations.
`CRC(CRC.Parameters crcParams)`

方法概要

所有方法静态方法实例方法具体方法
限定符和类型	方法和说明
`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()` This method should be called to retrieve actual CRC for the data processed so far.
`short`	`finalCRC16()` Is a convenience method to spare end users from explicit type conversion every time this package is used.
`int`	`finalCRC32()` Is a convenience method to spare end users from explicit type conversion every time this package is used.
`byte`	`finalCRC8()` 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(byte[] chunk)` A convenience method for feeding a complete byte array of data.
`long`	`update(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).

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 构造器详细资料
  - CRC
```
public CRC(CRC.Algorithm algorithm)
```
    Constructs a new CRC processor for table based CRC calculations. Underneath, it just calls finalCRC() method.
    
    参数:
    
    algorithm - CRC algorithm parameters
    
    抛出:
    
    RuntimeException - if CRC sum width is not divisible by 8
  - CRC
```
public CRC(CRC.Parameters crcParams)
```
- 方法详细资料
  - 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.
    
    参数:
    
    crcParams - CRC algorithm parameters
    
    data - data for the CRC calculation
    
    返回:
    
    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).
    
    返回:
    
    initial value for this CRC intermediate value
  - update
```
public long update(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.
    
    参数:
    
    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.
    
    返回:
    
    updated intermediate value for this CRC
  - update
```
public long update(byte[] chunk)
```
    A convenience method for feeding a complete byte array of data.
    
    参数:
    
    chunk - data chunk to b processed by this call
    
    返回:
    
    updated intermediate value for this CRC
  - finalCRC
```
public long finalCRC()
```
    This method should be called to retrieve actual CRC for the data processed so far.
    
    返回:
    
    calculated CRC
  - finalCRC8
```
public byte finalCRC8()
```
    Is a convenience method to spare end users from explicit type conversion every time this package is used. Underneath, it just calls finalCRC() method.
    
    返回:
    
    the final CRC value
    
    抛出:
    
    RuntimeException - if crc being calculated is not 8-bit
  - finalCRC16
```
public short finalCRC16()
```
    Is a convenience method to spare end users from explicit type conversion every time this package is used. Underneath, it just calls finalCRC() method.
    
    返回:
    
    the final CRC value
    
    抛出:
    
    RuntimeException - if crc being calculated is not 16-bit
  - finalCRC32
```
public int finalCRC32()
```
    Is a convenience method to spare end users from explicit type conversion every time this package is used. Underneath, it just calls finalCRC() method.
    
    返回:
    
    the final CRC value
    
    抛出:
    
    RuntimeException - if crc being calculated is not 32-bit

类 CRC

嵌套类概要

构造器概要

方法概要

从类继承的方法 java.lang.Object

构造器详细资料

CRC

CRC

方法详细资料

calculateCRC

calculateCRC

calculateCRC

calculateCRC

init

update

update

finalCRC

finalCRC8

finalCRC16

finalCRC32