luby/dist/encoder.js

Generate fountain codes / erasure codes (Luby Transform, robust)

"use strict";
var __importDefault = (this && this.__importDefault) || function (mod) {
    return (mod && mod.__esModule) ? mod : { "default": mod };
};
Object.defineProperty(exports, "__esModule", { value: true });
const distributions_1 = require("./distributions");
const selectNeighbours_1 = __importDefault(require("./selectNeighbours"));
class Symbol {
    constructor(index, degree, data, K) {
        this.index = index;
        this.degree = degree;
        this.data = data;
        this.K = K;
    }
}
function splitFile(file, blockSize) {
    let blocks = [];
    for (var i = 0; i < file.length; i += blockSize) {
        blocks.push(Array.from(file.slice(i, i + blockSize)));
    }
    if (blocks[blocks.length - 1].length < blockSize) {
        blocks[blocks.length - 1] = blocks[blocks.length - 1].concat(new Array(blockSize - blocks[blocks.length - 1].length).fill(0));
    }
    return blocks;
}
function choices(weights, k) {
    const choice = () => {
        const randomNr = Math.random();
        let threshold = 0;
        let winner = null;
        for (var i = 0; i < weights.length; i++) {
            threshold += weights[i];
            if (threshold > randomNr) {
                winner = i;
                return winner;
            }
        }
        return winner;
    };
    const _choices = [];
    for (let i = 0; i < k; i++) {
        _choices[i] = choice();
    }
    return _choices;
}
function getRandomDegrees(K, desiredNumberOfSymbols) {
    return [1, ...choices(distributions_1.generateRobustDistribution(K), desiredNumberOfSymbols)];
}
function encode(file, blockSize, seed = "None") {
    const sourceSymbols = splitFile(file, blockSize);
    const K = sourceSymbols.length;
    let desiredNumberOfSymbols = Math.floor(K * 1.7);
    if (desiredNumberOfSymbols < 65)
        desiredNumberOfSymbols = 65;
    const randomDegrees = getRandomDegrees(K, desiredNumberOfSymbols);
    const xaEncode = (arar) => arar.reduce((a, b) => {
        const out = [];
        for (let i = 0; i < arar[0].length; i++) {
            out.push(a[i] ^ b[i]);
        }
        return out;
    });
    const symbols = [];
    for (let i = 0; i < desiredNumberOfSymbols; i++) {
        const selectedNeighbours = selectNeighbours_1.default(i, randomDegrees[i], K);
        const data = xaEncode(selectedNeighbours.map(sn => sourceSymbols[sn]));
        symbols.push(new Symbol(i, selectedNeighbours.length, data, K));
    }
    return symbols;
}
exports.default = encode;
//# sourceMappingURL=encoder.js.map