@gandlaf21/bc-ur/dist/lib/es6/fountainUtils.js

A JS implementation of the Uniform Resources (UR) specification from Blockchain Commons

var __spreadArrays = (this && this.__spreadArrays) || function () {
    for (var s = 0, i = 0, il = arguments.length; i < il; i++) s += arguments[i].length;
    for (var r = Array(s), k = 0, i = 0; i < il; i++)
        for (var a = arguments[i], j = 0, jl = a.length; j < jl; j++, k++)
            r[k] = a[j];
    return r;
};
import { intToBytes } from "./utils";
import Xoshiro from "./xoshiro";
// @ts-ignore
import randomSampler from '@apocentre/alias-sampling';
import { Buffer } from "buffer";
export var chooseDegree = function (seqLenth, rng) {
    var degreeProbabilities = __spreadArrays(new Array(seqLenth)).map(function (_, index) { return 1 / (index + 1); });
    var degreeChooser = randomSampler(degreeProbabilities, null, rng.nextDouble);
    return degreeChooser.next() + 1;
};
export var shuffle = function (items, rng) {
    var remaining = __spreadArrays(items);
    var result = [];
    while (remaining.length > 0) {
        var index = rng.nextInt(0, remaining.length - 1);
        var item = remaining[index];
        // remaining.erase(remaining.begin() + index);
        remaining.splice(index, 1);
        result.push(item);
    }
    return result;
};
export var chooseFragments = function (seqNum, seqLength, checksum) {
    // The first `seqLenth` parts are the "pure" fragments, not mixed with any
    // others. This means that if you only generate the first `seqLenth` parts,
    // then you have all the parts you need to decode the message.
    if (seqNum <= seqLength) {
        return [seqNum - 1];
    }
    else {
        var seed = Buffer.concat([intToBytes(seqNum), intToBytes(checksum)]);
        var rng = new Xoshiro(seed);
        var degree = chooseDegree(seqLength, rng);
        var indexes = __spreadArrays(new Array(seqLength)).map(function (_, index) { return index; });
        var shuffledIndexes = shuffle(indexes, rng);
        return shuffledIndexes.slice(0, degree);
    }
};
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