message: Add comment to explain why need to put condition out of loop.
diff: @@ -63,6 +63,8 @@ typename Distribution::ResultType VectorizedFormat(
  }
  }
  // Tail processing if any.
  + // Put the tail condition out of above loop to improve performance:
  + // it will be executed only once and save time on CPU.
  if (offset < kResultElementCount) {
  sample = (*gen)();
  for (int i = 0; offset < kResultElementCount; i++, offset++) {
  