autoCorrelation optimization

autoCorrelation.diff

function autoCorrelation(arr) {
  var ac = new Float32Array(2048);
  for (var lag = 0; lag < arr.length; lag++) {
    var value = 0;
    for (var index = 0; index < arr.length - lag; index++) {
      let a = arr[index];
-     let b = arr[index-lag];
+     let otherindex = index - lag;
+     let b = otherindex >= 0 ? arr[index-lag] : 0;
      value = value + a * b;
    }
    ac[lag] = value;
  }
  return ac;
}