Package com.scurrilous.circe.params

Class CrcParameters

java.lang.Object

com.scurrilous.circe.params.CrcParameters

All Implemented Interfaces:

HashParameters

public class CrcParameters
extends Object
implements HashParameters

Hash parameters used to define a cyclic redundancy check (CRC). Includes some commonly used sets of parameters.

Field Summary

Fields

Modifier and Type	Field	Description
static final CrcParameters	CRC16	Parameters for CRC-16, used in the ARC and LHA compression utilities.
static final CrcParameters	CRC16_CCITT	Parameters for CRC-16/CCITT, used in the Kermit protocol.
static final CrcParameters	CRC16_XMODEM	Parameters for CRC-16/XMODEM, used in the XMODEM protocol.
static final CrcParameters	CRC32	Parameters for CRC-32, used in Ethernet, SATA, PKZIP, ZMODEM, etc.
static final CrcParameters	CRC32_BZIP2	Parameters for CRC-32/BZIP2, used in BZIP2.
static final CrcParameters	CRC32_MPEG2	Parameters for CRC-32/MPEG-2, used in MPEG-2.
static final CrcParameters	CRC32_POSIX	Parameters for CRC-32/POSIX, used in the cksum utility.
static final CrcParameters	CRC32C	Parameters for CRC-32C, used in iSCSI and SCTP.
static final CrcParameters	CRC64	Parameters for CRC-64, used in the ECMA-182 standard for DLT-1 tapes.
static final CrcParameters	CRC64_XZ	Parameters for CRC-64/XZ, used in the .xz file format.

Constructor Summary

Constructors

Constructor	Description
CrcParameters(String name, int bitWidth, long polynomial, long initial, long xorOut, boolean reflected)	Constructs a CrcParameters with the given parameters.

Method Summary

Modifier and Type	Method	Description
String	algorithm()	Returns the canonical name of the hash algorithm.
int	bitWidth()	Returns the width in bits of the CRC function.
boolean	equals(Object obj)
int	hashCode()
long	initial()	Returns the initial value of the CRC register.
boolean	match(int bitWidth, long polynomial, long initial, long xorOut, boolean reflected)	Returns whether this object matches the given CRC parameters.
long	polynomial()	Returns the binary form of polynomial that defines the CRC function (with the implicit top bit omitted).
boolean	reflected()	Returns whether the CRC function is "reflected".
long	xorOut()	Returns the value XOR'ed with the CRC register when it is read to determine the output value.

Methods inherited from class java.lang.Object

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

Field Details

CRC16

public static final CrcParameters CRC16

Parameters for CRC-16, used in the ARC and LHA compression utilities.

CRC16_CCITT

public static final CrcParameters CRC16_CCITT

Parameters for CRC-16/CCITT, used in the Kermit protocol.

CRC16_XMODEM

public static final CrcParameters CRC16_XMODEM

Parameters for CRC-16/XMODEM, used in the XMODEM protocol.

CRC32

public static final CrcParameters CRC32

Parameters for CRC-32, used in Ethernet, SATA, PKZIP, ZMODEM, etc.

CRC32_BZIP2

public static final CrcParameters CRC32_BZIP2

Parameters for CRC-32/BZIP2, used in BZIP2.

CRC32C

public static final CrcParameters CRC32C

Parameters for CRC-32C, used in iSCSI and SCTP.

CRC32_MPEG2

public static final CrcParameters CRC32_MPEG2

Parameters for CRC-32/MPEG-2, used in MPEG-2.

CRC32_POSIX

public static final CrcParameters CRC32_POSIX

Parameters for CRC-32/POSIX, used in the cksum utility.

CRC64

public static final CrcParameters CRC64

Parameters for CRC-64, used in the ECMA-182 standard for DLT-1 tapes.

CRC64_XZ

public static final CrcParameters CRC64_XZ

Parameters for CRC-64/XZ, used in the .xz file format.

Constructor Details

CrcParameters

public CrcParameters(String name,
 int bitWidth,
 long polynomial,
 long initial,
 long xorOut,
 boolean reflected)

Constructs a CrcParameters with the given parameters.

Parameters:

name - the canonical name of the CRC function

bitWidth - the width of the CRC function

polynomial - the polynomial in binary form (non-reflected)

initial - the initial value of the CRC register

xorOut - a value XOR'ed with the CRC when it is read

reflected - indicates whether the CRC is reflected (LSB-first)

Throws:

IllegalArgumentException - if the width is less than 1 or greater than 64

Method Details

algorithm

public String algorithm()

Description copied from interface: HashParameters

Returns the canonical name of the hash algorithm.

Specified by:

algorithm in interface HashParameters

Returns:

the name of the hash algorithm

bitWidth

public int bitWidth()

Returns the width in bits of the CRC function. The width is also the position of the implicit set bit at the top of the polynomial.

Returns:

the CRC width in bits

polynomial

public long polynomial()

Returns the binary form of polynomial that defines the CRC function (with the implicit top bit omitted). For instance, the CRC-16 polynomial x¹⁶ + x¹⁵ + x² + 1 is represented as 1000 0000 0000 0101 (0x8005).

Returns:

the CRC polynomial

initial

public long initial()

Returns the initial value of the CRC register.

Returns:

the CRC initial value

xorOut

public long xorOut()

Returns the value XOR'ed with the CRC register when it is read to determine the output value.

Returns:

the final XOR value

reflected

public boolean reflected()

Returns whether the CRC function is "reflected". Reflected CRCs process data LSB-first, whereas "normal" CRCs are MSB-first.

Returns:

whether the CRC function is reflected

match

public boolean match(int bitWidth,
 long polynomial,
 long initial,
 long xorOut,
 boolean reflected)

Returns whether this object matches the given CRC parameters.

Parameters:

bitWidth - the width of the CRC function

polynomial - the polynomial in binary form (non-reflected)

initial - the initial value of the CRC register

xorOut - a value XOR'ed with the CRC when it is read

reflected - indicates whether the CRC is reflected (LSB-first)

Returns:

true if all parameters match exactly, false otherwise

equals

public boolean equals(Object obj)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object