Package com.google.zxing.common.reedsolomon

Class GenericGF

java.lang.Object

com.google.zxing.common.reedsolomon.GenericGF

public final class GenericGF
extends java.lang.Object

This class contains utility methods for performing mathematical operations over the Galois Fields. Operations use a given primitive polynomial in calculations.

Throughout this package, elements of the GF are represented as an int for convenience and speed (but at the cost of memory).

The size of the GF is assumed to be a power of two.

Field Summary

Fields

Modifier and Type	Field	Description
static GenericGF	AZTEC_DATA_10
static GenericGF	AZTEC_DATA_12
static GenericGF	AZTEC_DATA_6
static GenericGF	AZTEC_DATA_8
static GenericGF	AZTEC_PARAM
static GenericGF	DATA_MATRIX_FIELD_256
private int[]	expTable
private int	generatorBase
private int[]	logTable
static GenericGF	MAXICODE_FIELD_64
private GenericGFPoly	one
private int	primitive
static GenericGF	QR_CODE_FIELD_256
private int	size
private GenericGFPoly	zero

Constructor Summary

Constructors

Constructor	Description
GenericGF(int primitive, int size, int b)	Create a representation of GF(size) using the given primitive polynomial.

Method Summary

Modifier and Type	Method	Description
(package private) static int	addOrSubtract(int a, int b)	Implements both addition and subtraction -- they are the same in GF(size).
(package private) GenericGFPoly	buildMonomial(int degree, int coefficient)
(package private) int	exp(int a)
int	getGeneratorBase()
(package private) GenericGFPoly	getOne()
int	getSize()
(package private) GenericGFPoly	getZero()
(package private) int	inverse(int a)
(package private) int	log(int a)
(package private) int	multiply(int a, int b)
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

AZTEC_DATA_12

public static final GenericGF AZTEC_DATA_12

AZTEC_DATA_10

public static final GenericGF AZTEC_DATA_10

AZTEC_DATA_6

public static final GenericGF AZTEC_DATA_6

AZTEC_PARAM

public static final GenericGF AZTEC_PARAM

QR_CODE_FIELD_256

public static final GenericGF QR_CODE_FIELD_256

DATA_MATRIX_FIELD_256

public static final GenericGF DATA_MATRIX_FIELD_256

AZTEC_DATA_8

public static final GenericGF AZTEC_DATA_8

MAXICODE_FIELD_64

public static final GenericGF MAXICODE_FIELD_64

expTable

private final int[] expTable

logTable

private final int[] logTable

zero

private final GenericGFPoly zero

one

private final GenericGFPoly one

size

private final int size

primitive

private final int primitive

generatorBase

private final int generatorBase

Constructor Detail

GenericGF

public GenericGF(int primitive,
                 int size,
                 int b)

Create a representation of GF(size) using the given primitive polynomial.

Parameters:

primitive - irreducible polynomial whose coefficients are represented by the bits of an int, where the least-significant bit represents the constant coefficient

size - the size of the field

b - the factor b in the generator polynomial can be 0- or 1-based (g(x) = (x+a^b)(x+a^(b+1))...(x+a^(b+2t-1))). In most cases it should be 1, but for QR code it is 0.

Method Detail

getZero

GenericGFPoly getZero()

getOne

GenericGFPoly getOne()

buildMonomial

GenericGFPoly buildMonomial(int degree,
                            int coefficient)

Returns:

the monomial representing coefficient * x^degree

addOrSubtract

static int addOrSubtract(int a,
                         int b)

Implements both addition and subtraction -- they are the same in GF(size).

Returns:

sum/difference of a and b

exp

int exp(int a)

Returns:

2 to the power of a in GF(size)

log

int log(int a)

Returns:

base 2 log of a in GF(size)

inverse

int inverse(int a)

Returns:

multiplicative inverse of a

multiply

int multiply(int a,
             int b)

Returns:

product of a and b in GF(size)

getSize

public int getSize()

getGeneratorBase

public int getGeneratorBase()

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object