59 lines
1.7 KiB
JavaScript
59 lines
1.7 KiB
JavaScript
var BufferUtil = require('../utils/buffer')
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var Polynomial = require('./polynomial')
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var Buffer = require('buffer').Buffer
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function ReedSolomonEncoder (degree) {
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this.genPoly = undefined
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this.degree = degree
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if (this.degree) this.initialize(this.degree)
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}
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/**
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* Initialize the encoder.
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* The input param should correspond to the number of error correction codewords.
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*
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* @param {Number} degree
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*/
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ReedSolomonEncoder.prototype.initialize = function initialize (degree) {
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// create an irreducible generator polynomial
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this.degree = degree
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this.genPoly = Polynomial.generateECPolynomial(this.degree)
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}
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/**
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* Encodes a chunk of data
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*
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* @param {Buffer} data Buffer containing input data
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* @return {Buffer} Buffer containing encoded data
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*/
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ReedSolomonEncoder.prototype.encode = function encode (data) {
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if (!this.genPoly) {
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throw new Error('Encoder not initialized')
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}
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// Calculate EC for this data block
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// extends data size to data+genPoly size
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var pad = BufferUtil.alloc(this.degree)
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var paddedData = Buffer.concat([data, pad], data.length + this.degree)
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// The error correction codewords are the remainder after dividing the data codewords
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// by a generator polynomial
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var remainder = Polynomial.mod(paddedData, this.genPoly)
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// return EC data blocks (last n byte, where n is the degree of genPoly)
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// If coefficients number in remainder are less than genPoly degree,
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// pad with 0s to the left to reach the needed number of coefficients
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var start = this.degree - remainder.length
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if (start > 0) {
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var buff = BufferUtil.alloc(this.degree)
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remainder.copy(buff, start)
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return buff
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}
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return remainder
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}
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module.exports = ReedSolomonEncoder
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