multiply = (out, a, b) => {
  const a00 = a[0]
  const a01 = a[1]
  const a02 = a[2]
  const a03 = a[3]
  const a10 = a[4]
  const a11 = a[5]
  const a12 = a[6]
  const a13 = a[7]
  const a20 = a[8]
  const a21 = a[9]
  const a22 = a[10]
  const a23 = a[11]
  const a30 = a[12]
  const a31 = a[13]
  const a32 = a[14]
  const a33 = a[15]

  // Cache only the current line of the second matrix
  let b0 = b[0]
  let b1 = b[1]
  let b2 = b[2]
  let b3 = b[3]
  out[0] = b0 * a00 + b1 * a10 + b2 * a20 + b3 * a30
  out[1] = b0 * a01 + b1 * a11 + b2 * a21 + b3 * a31
  out[2] = b0 * a02 + b1 * a12 + b2 * a22 + b3 * a32
  out[3] = b0 * a03 + b1 * a13 + b2 * a23 + b3 * a33

  b0 = b[4]
  b1 = b[5]
  b2 = b[6]
  b3 = b[7]
  out[4] = b0 * a00 + b1 * a10 + b2 * a20 + b3 * a30
  out[5] = b0 * a01 + b1 * a11 + b2 * a21 + b3 * a31
  out[6] = b0 * a02 + b1 * a12 + b2 * a22 + b3 * a32
  out[7] = b0 * a03 + b1 * a13 + b2 * a23 + b3 * a33

  b0 = b[8]
  b1 = b[9]
  b2 = b[10]
  b3 = b[11]
  out[8] = b0 * a00 + b1 * a10 + b2 * a20 + b3 * a30
  out[9] = b0 * a01 + b1 * a11 + b2 * a21 + b3 * a31
  out[10] = b0 * a02 + b1 * a12 + b2 * a22 + b3 * a32
  out[11] = b0 * a03 + b1 * a13 + b2 * a23 + b3 * a33

  b0 = b[12]
  b1 = b[13]
  b2 = b[14]
  b3 = b[15]
  out[12] = b0 * a00 + b1 * a10 + b2 * a20 + b3 * a30
  out[13] = b0 * a01 + b1 * a11 + b2 * a21 + b3 * a31
  out[14] = b0 * a02 + b1 * a12 + b2 * a22 + b3 * a32
  out[15] = b0 * a03 + b1 * a13 + b2 * a23 + b3 * a33
  return out
}
Multiplies the two matrices.

@param {mat4} out - receiving matrix
@param {mat4} a - first operand
@param {mat4} b - second operand
@returns {mat4} out
@alias module:modeling/maths/mat4.multiply