count-loop.html

<!DOCTYPE html>
<html>
    <head>
        <meta charset='utf-8'>
    </head>
    <body>
        <script>

function appendBody(x) {
    const e = document.createElement('div');
    e.innerHTML = x;
    document.body.appendChild(e);
}

function prettyTime(x) {
    let suffix = 'ms';
    if (x < 1) {
        x *= 1000;
        suffix = 'us';
    }
    if (x < 1) {
        x *= 1000;
        suffix = 'ns';
    }
    return x + suffix;
}

function report(x, y) {
    appendBody('Workload of ' + x + ' in ' + prettyTime(y) + ': ' + prettyTime(y / x) + '/work');
}

let foo = 7;
function count(n) {
    const mult = 100;
    const start = performance.now();
    for (let i = 0; i < n*mult; i++) {
        foo = (foo|0) + 1;
    }
    const diff = performance.now() - start;
    if (diff) {
        report(n, diff);
    }
    return diff;
}

function seek_magnitude_from_below(func, goalpost, start_at) {
    let x = start_at || 1;
    while (true) {
        const y = func(x);
        if (y > goalpost)
            return [x, y];
        x *= 2;
    }
}

seek_magnitude_from_below(count, 300);

        </script>
    </body>
</html>