mirror of
https://github.com/cwinfo/matterbridge.git
synced 2024-12-27 10:05:39 +00:00
74 lines
2.3 KiB
Go
74 lines
2.3 KiB
Go
// go-qrcode
|
|
// Copyright 2014 Tom Harwood
|
|
|
|
// Package reedsolomon provides error correction encoding for QR Code 2005.
|
|
//
|
|
// QR Code 2005 uses a Reed-Solomon error correcting code to detect and correct
|
|
// errors encountered during decoding.
|
|
//
|
|
// The generated RS codes are systematic, and consist of the input data with
|
|
// error correction bytes appended.
|
|
package reedsolomon
|
|
|
|
import (
|
|
"log"
|
|
|
|
bitset "github.com/skip2/go-qrcode/bitset"
|
|
)
|
|
|
|
// Encode data for QR Code 2005 using the appropriate Reed-Solomon code.
|
|
//
|
|
// numECBytes is the number of error correction bytes to append, and is
|
|
// determined by the target QR Code's version and error correction level.
|
|
//
|
|
// ISO/IEC 18004 table 9 specifies the numECBytes required. e.g. a 1-L code has
|
|
// numECBytes=7.
|
|
func Encode(data *bitset.Bitset, numECBytes int) *bitset.Bitset {
|
|
// Create a polynomial representing |data|.
|
|
//
|
|
// The bytes are interpreted as the sequence of coefficients of a polynomial.
|
|
// The last byte's value becomes the x^0 coefficient, the second to last
|
|
// becomes the x^1 coefficient and so on.
|
|
ecpoly := newGFPolyFromData(data)
|
|
ecpoly = gfPolyMultiply(ecpoly, newGFPolyMonomial(gfOne, numECBytes))
|
|
|
|
// Pick the generator polynomial.
|
|
generator := rsGeneratorPoly(numECBytes)
|
|
|
|
// Generate the error correction bytes.
|
|
remainder := gfPolyRemainder(ecpoly, generator)
|
|
|
|
// Combine the data & error correcting bytes.
|
|
// The mathematically correct answer is:
|
|
//
|
|
// result := gfPolyAdd(ecpoly, remainder).
|
|
//
|
|
// The encoding used by QR Code 2005 is slightly different this result: To
|
|
// preserve the original |data| bit sequence exactly, the data and remainder
|
|
// are combined manually below. This ensures any most significant zero bits
|
|
// are preserved (and not optimised away).
|
|
result := bitset.Clone(data)
|
|
result.AppendBytes(remainder.data(numECBytes))
|
|
|
|
return result
|
|
}
|
|
|
|
// rsGeneratorPoly returns the Reed-Solomon generator polynomial with |degree|.
|
|
//
|
|
// The generator polynomial is calculated as:
|
|
// (x + a^0)(x + a^1)...(x + a^degree-1)
|
|
func rsGeneratorPoly(degree int) gfPoly {
|
|
if degree < 2 {
|
|
log.Panic("degree < 2")
|
|
}
|
|
|
|
generator := gfPoly{term: []gfElement{1}}
|
|
|
|
for i := 0; i < degree; i++ {
|
|
nextPoly := gfPoly{term: []gfElement{gfExpTable[i], 1}}
|
|
generator = gfPolyMultiply(generator, nextPoly)
|
|
}
|
|
|
|
return generator
|
|
}
|