BigInt Ra NDom

shittyrand.js

function findClosestBits(n) {
    return BigInt('0b' + n.toString(2).replaceAll('0', '1'))
}

// Returns a uniform random value in [0, max)
function rand(max) {
    if (max <= 0) throw new Error("Argument max must be > 0");
    if (max > 0xFFFFFFFFFFFFFFFFn) throw new Error("Argument max must be <= 0xFFFFFFFFFFFFFFFF");
    const randomNumber = new BigUint64Array(1);
    crypto.getRandomValues(randomNumber);
    
    let ourNumber;
    do {
        const bytesToHoldMax = findClosestBits(max);
        const randomNumberInOurRange = randomNumber[0] & bytesToHoldMax;
        ourNumber = randomNumberInOurRange;
        crypto.getRandomValues(randomNumber);
    } while (ourNumber > max);

    return ourNumber;   
}