ltcode/dist/app/prng.js

Luby Transform Code implementation.

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.PRNG = void 0;
class PRNG {
    constructor(numBlocks, seed) {
        this.DEFAULT_DELTA = 0.5;
        this.PRNG_M = 2147483647;
        this.seed = seed;
        this.numBlocks = numBlocks;
        this.cumulativeDistributionFunction = this.generateRsdCdf();
    }
    sample_source_blocks(seed) {
        const initialSamplingSeed = seed !== null ? seed : this.seed;
        if (seed !== null) {
            this.seed = seed;
        }
        const degree = this.sampleDegree();
        const selectedBlocks = new Set();
        while (selectedBlocks.size < degree) {
            const nextRandom = this.nextRandom();
            const blockNumber = nextRandom % this.numBlocks;
            selectedBlocks.add(blockNumber);
        }
        return [initialSamplingSeed, selectedBlocks];
    }
    nextRandom() {
        this.seed = 16807 * this.seed % this.PRNG_M;
        return this.seed;
    }
    sampleDegree() {
        const probability = this.nextRandom() / (this.PRNG_M - 1);
        for (let index = 0; index < this.cumulativeDistributionFunction.length; index++) {
            if (this.cumulativeDistributionFunction[index] > probability) {
                return index + 1;
            }
        }
        return this.cumulativeDistributionFunction.length;
    }
    generateTau(S) {
        const pivot = Math.floor(this.numBlocks / S);
        const tau = Array.from({ length: pivot - 1 }, (_, d) => S / this.numBlocks / (d + 1));
        tau.push(S / this.numBlocks * Math.log(S / this.DEFAULT_DELTA));
        tau.push(...Array.from({ length: this.numBlocks - pivot }, () => 0));
        return tau;
    }
    generateRho() {
        return [1 / this.numBlocks, ...Array.from({ length: this.numBlocks - 1 }, (_, d) => 1 / ((d + 2) * (d + 1)))];
    }
    generateMu() {
        const S = Math.log(this.numBlocks / this.DEFAULT_DELTA) * Math.sqrt(this.numBlocks) * 0.1;
        const tau = this.generateTau(S);
        const rho = this.generateRho();
        const normalizer = this.sum(rho) + this.sum(tau);
        return Array.from({ length: this.numBlocks }, (_, d) => (rho[d] + tau[d]) / normalizer);
    }
    sum(arr) {
        return arr.reduce((a, b) => a + b, 0);
    }
    generateRsdCdf() {
        const mu = this.generateMu();
        const arr = [];
        for (let d = 0; d < this.numBlocks; d++) {
            const slice_mu = mu.slice(0, d + 1);
            arr.push(this.sum(slice_mu));
        }
        return arr;
    }
}
exports.PRNG = PRNG;