function insertTwoSpacing(v) {
  v = (v ^ (v << 16)) & 0x030000ff;
  v = (v ^ (v << 8)) & 0x0300f00f;
  v = (v ^ (v << 4)) & 0x030c30c3;
  v = (v ^ (v << 2)) & 0x09249249;
  return v;
}
Inserts two 0 bits of spacing between a number's bits. This is the opposite of removeTwoSpacing.

Example:
 input: 6
 input (binary):  110
 output (binary): 1001000
                   ^^ ^^ (added)
 output: 72

@private
@param {number} v A 10-bit unsigned integer.
@returns {number} A 30-bit unsigned integer.
@see {@link https://fgiesen.wordpress.com/2009/12/13/decoding-morton-codes/}