function multiply$8(out, a, b) {
    var a0 = a[0],
        a1 = a[1],
        a2 = a[2],
        a3 = a[3];
    var b0 = b[0],
        b1 = b[1],
        b2 = b[2],
        b3 = b[3];
    out[0] = a0 * b0 + a2 * b1;
    out[1] = a1 * b0 + a3 * b1;
    out[2] = a0 * b2 + a2 * b3;
    out[3] = a1 * b2 + a3 * b3;
    return out;
  }
Multiplies two mat2's

@param {mat2} out the receiving matrix
@param {ReadonlyMat2} a the first operand
@param {ReadonlyMat2} b the second operand
@returns {mat2} out