setup-python/node_modules/w3c-hr-time/lib/clock-is-accurate.js
Danny McCormick 39c08a0eaa Initial pass
2019-06-26 21:12:00 -04:00

62 lines
1.4 KiB
JavaScript

"use strict";
const { hrtime } = require("./utils");
// The HR-TIME spec calls for 5-μs accuracy. Check that we have that in both hrtime() and Date.now().
function testClockAccuracy() {
// Test hrtime() first. The check is simpler and more stable, and we use hrtime() to measure Date.now()'s performance.
const roundTrip = hrtime(hrtime());
if (roundTrip[0] > 1 || roundTrip[1] > 5e3 * 2) {
return false;
}
// Test Date.now() twice: first with a looser bound (10 μs) but with a smaller run time to filter out very bad
// Date.now() performance, and then with a tighter bound (5 μs) to check we have the accuracy we need.
let times;
// eslint-disable-next-line no-unused-vars
let cur;
let start;
let end;
times = 100;
start = hrtime();
while (times-- > 0) {
cur = Date.now();
}
end = hrtime(start);
if ((end[0] * 1e9 + end[1]) > 1000000) {
return false;
}
times = 10000;
start = hrtime();
while (times-- > 0) {
cur = Date.now();
}
end = hrtime(start);
if ((end[0] * 1e9 + end[1]) > 50000000) {
return false;
}
return true;
}
// Warm up the function.
testClockAccuracy();
testClockAccuracy();
testClockAccuracy();
const TIMES = 5;
const THRESHOLD = 0.6 * TIMES;
let accurates = 0;
for (let i = 0; i < TIMES; i++) {
if (testClockAccuracy()) {
accurates++;
}
}
const isAccurate = accurates >= THRESHOLD;
module.exports = isAccurate;