function readZigZag(reader) {
  const zigzag = readVarInt(reader)
  // convert zigzag to int
  return zigzag >>> 1 ^ -(zigzag & 1)
}
Values of type int32 and int64 are transformed to a zigzag int.
A zigzag int folds positive and negative numbers into the positive number space.

@param {DataReader} reader
@returns {number}