package gf256

import "rsc.io/qr/gf256"

Package gf256 implements arithmetic over the Galois Field GF(256).

Index ¶

• type Field
• func NewField(poly, α int) *Field
• func (f *Field) Add(x, y byte) byte
• func (f *Field) Exp(e int) byte
• func (f *Field) Inv(x byte) byte
• func (f *Field) Log(x byte) int
• func (f *Field) Mul(x, y byte) byte
• type RSEncoder
• func NewRSEncoder(f *Field, c int) *RSEncoder
• func (rs *RSEncoder) ECC(data []byte, check []byte)

Types ¶

type Field ¶

type Field struct {
	// contains filtered or unexported fields
}

A Field represents an instance of GF(256) defined by a specific polynomial.

func NewField ¶

func NewField(poly, α int) *Field

NewField returns a new field corresponding to the polynomial poly and generator α. The Reed-Solomon encoding in QR codes uses polynomial 0x11d with generator 2.

The choice of generator α only affects the Exp and Log operations.

func (*Field) Add ¶

func (f *Field) Add(x, y byte) byte

Add returns the sum of x and y in the field.

func (*Field) Exp ¶

func (f *Field) Exp(e int) byte

Exp returns the base-α exponential of e in the field. If e < 0, Exp returns 0.

func (*Field) Inv ¶

func (f *Field) Inv(x byte) byte

Inv returns the multiplicative inverse of x in the field. If x == 0, Inv returns 0.

func (*Field) Log ¶

func (f *Field) Log(x byte) int

Log returns the base-α logarithm of x in the field. If x == 0, Log returns -1.

func (*Field) Mul ¶

func (f *Field) Mul(x, y byte) byte

Mul returns the product of x and y in the field.

type RSEncoder ¶

type RSEncoder struct {
	// contains filtered or unexported fields
}

An RSEncoder implements Reed-Solomon encoding over a given field using a given number of error correction bytes.

func NewRSEncoder ¶

func NewRSEncoder(f *Field, c int) *RSEncoder

NewRSEncoder returns a new Reed-Solomon encoder over the given field and number of error correction bytes.

func (*RSEncoder) ECC ¶

func (rs *RSEncoder) ECC(data []byte, check []byte)

ECC writes to check the error correcting code bytes for data using the given Reed-Solomon parameters.

Source Files ¶

gf256.go