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