luby/dist/distributions.js

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

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.generateRobustDistribution = exports.generateIdealDistribution = void 0;
exports.generateIdealDistribution = function (K) {
    let probabilities = [0, 1 / K];
    for (var i = 2; i <= K; i++) {
        probabilities.push(1 / (i * (i - 1)));
    }
    return probabilities;
};
exports.generateRobustDistribution = function (K) {
    const ROBUST_FAILURE_PROBABILITY = 0.01;
    const spikeIndex = Math.floor(K / 2) + 1;
    const rrrrr = K / spikeIndex;
    let extra_proba = [0];
    for (var i = 1; i < spikeIndex; i++) {
        extra_proba[i] = 1 / (i * spikeIndex);
    }
    extra_proba.push(Math.log(rrrrr / ROBUST_FAILURE_PROBABILITY) / spikeIndex);
    extra_proba = extra_proba.concat(new Array(K - spikeIndex).fill(0));
    const ideal = exports.generateIdealDistribution(K);
    extra_proba = extra_proba.map((a, i) => {
        const b = ideal[i] || 0;
        return a + b;
    });
    const epSum = extra_proba.reduce((a, b) => a + b, 0);
    return extra_proba.map((val) => val / epSum);
};
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