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62 lines
1.6 KiB
62 lines
1.6 KiB
const GF = require('./galois-field')
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/**
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* Multiplies two polynomials inside Galois Field
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*
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* @param {Uint8Array} p1 Polynomial
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* @param {Uint8Array} p2 Polynomial
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* @return {Uint8Array} Product of p1 and p2
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*/
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exports.mul = function mul (p1, p2) {
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const coeff = new Uint8Array(p1.length + p2.length - 1)
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for (let i = 0; i < p1.length; i++) {
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for (let j = 0; j < p2.length; j++) {
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coeff[i + j] ^= GF.mul(p1[i], p2[j])
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}
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}
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return coeff
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}
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/**
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* Calculate the remainder of polynomials division
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*
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* @param {Uint8Array} divident Polynomial
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* @param {Uint8Array} divisor Polynomial
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* @return {Uint8Array} Remainder
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*/
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exports.mod = function mod (divident, divisor) {
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let result = new Uint8Array(divident)
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while ((result.length - divisor.length) >= 0) {
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const coeff = result[0]
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for (let i = 0; i < divisor.length; i++) {
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result[i] ^= GF.mul(divisor[i], coeff)
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}
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// remove all zeros from buffer head
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let offset = 0
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while (offset < result.length && result[offset] === 0) offset++
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result = result.slice(offset)
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}
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return result
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}
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/**
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* Generate an irreducible generator polynomial of specified degree
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* (used by Reed-Solomon encoder)
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*
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* @param {Number} degree Degree of the generator polynomial
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* @return {Uint8Array} Buffer containing polynomial coefficients
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*/
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exports.generateECPolynomial = function generateECPolynomial (degree) {
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let poly = new Uint8Array([1])
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for (let i = 0; i < degree; i++) {
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poly = exports.mul(poly, new Uint8Array([1, GF.exp(i)]))
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}
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return poly
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}
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