Run results for: atan2 vs acos

Run details:

User agent: Mozilla/5.0 (Linux; Android 10; GM1915 Build/QKQ1.190716.003; ) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/87.0.4280.141 Mobile Safari/537.36 BingSapphire/23.4.401008302

Browser: Chrome Mobile 87

Operating system: Android

Device Platform: Mobile

Date tested: 2 years ago

Test name	Executions per second
acos	1.3 Ops/sec
atan2	3.3 Ops/sec

Script Preparation code:

var N = 1000000;
var x = new Float32Array(N);
var y = new Float32Array(N);

for (var i = 0; i < N; ++i) {
    x[i] = 100 * Math.random();
    y[i] = 100 * Math.random();
}

Tests:

acos
var fn = Math.acos; for (var i = 0; i < N; ++i) { fn(x[i]/Math.sqrt(x[i]*x[i]+y[i]*y[i])); }
atan2
var fn = Math.atan; for (var i = 0; i < N; ++i) { fn(y[i], x[i]); }