improve bigFactorial algorithm

You can use different algorithms of factorial to speed this 2-8 times. Universal one (twice as fast): [i am using bigint’s in implementation, but logic is the same]

function factorial(n) {
  if(n === 0n || n === 1n) {
    return 1n;
  }
  if(n % 2n === 1n) {
    return n * factorial(n - 1n);
  }

  let p = n;
  let prod = n;

  while(p > 2n) {
    p -= 2n;
    n += p;

    prod *= n;
  }

  return prod;
}

If you are interested in the less universal (faster than this after n=1400), I could provide it in comment

[josdejong]

👍 good luck with your exams

[bartekleon]

@josdejong the problem is that BigInt(5) is slow, and 5n will throw an error if a browser doesn’t support BigInt 😕 well… I’ll see what can be done to squeeze as much performance as I can