1<!DOCTYPE html>
2<script src="/resources/testharness.js"></script>
3<script src="/resources/testharnessreport.js"></script>
4<script type="text/javascript">
5'use strict';
6
7// Computes greatest common divisor of a and b using Euclid's algorithm
8function computeGCD(a, b) {
9  if (!Number.isInteger(a) || !Number.isInteger(b)) {
10    throw new Error('Parameters must be integer numbers');
11  }
12
13  var r;
14  while (b != 0) {
15    r = a % b;
16    a = b;
17    b = r;
18  }
19  return (a < 0) ? -a : a;
20}
21
22// Finds minimum resolution Δ given a set of samples which are known to be in the form of N*Δ.
23// We use GCD of all samples as a simple estimator.
24function estimateMinimumResolution(samples) {
25  var gcd;
26  for (const sample of samples) {
27    gcd = gcd ? computeGCD(gcd, sample) : sample;
28  }
29
30  return gcd;
31}
32
33test(function() {
34  const samples = [];
35  for (var i = 0; i < 1e3; i++) {
36    var deltaInMicroSeconds = 0;
37    const e1 = new MouseEvent('test1');
38    do {
39      const e2 = new MouseEvent('test2');
40      deltaInMicroSeconds = Math.round((e2.timeStamp - e1.timeStamp) * 1000);
41    } while (deltaInMicroSeconds == 0) // only collect non-zero samples
42
43    samples.push(deltaInMicroSeconds);
44  }
45
46  const minResolution = estimateMinimumResolution(samples);
47  assert_greater_than_equal(minResolution, 5);
48}, 'Event timestamp should not have a resolution better than 5 microseconds');
49</script>