multiply.js

module.exports = multiply

/**
 * Multiplies two mat3's
 *
 * @alias mat3.multiply
 * @param {mat3} out the receiving matrix
 * @param {mat3} a the first operand
 * @param {mat3} b the second operand
 * @returns {mat3} out
 */
function multiply(out, a, b) {
  var a00 = a[0], a01 = a[1], a02 = a[2]
  var a10 = a[3], a11 = a[4], a12 = a[5]
  var a20 = a[6], a21 = a[7], a22 = a[8]

  var b00 = b[0], b01 = b[1], b02 = b[2]
  var b10 = b[3], b11 = b[4], b12 = b[5]
  var b20 = b[6], b21 = b[7], b22 = b[8]

  out[0] = b00 * a00 + b01 * a10 + b02 * a20
  out[1] = b00 * a01 + b01 * a11 + b02 * a21
  out[2] = b00 * a02 + b01 * a12 + b02 * a22

  out[3] = b10 * a00 + b11 * a10 + b12 * a20
  out[4] = b10 * a01 + b11 * a11 + b12 * a21
  out[5] = b10 * a02 + b11 * a12 + b12 * a22

  out[6] = b20 * a00 + b21 * a10 + b22 * a20
  out[7] = b20 * a01 + b21 * a11 + b22 * a21
  out[8] = b20 * a02 + b21 * a12 + b22 * a22

  return out
}