code: func addScalars(a []byte, b []byte) []byte {
  	aInt := new(big.Int).SetBytes(a)
  	bInt := new(big.Int).SetBytes(b)
  	sInt := new(big.Int).Add(aInt, bInt)
  	x := sInt.Mod(sInt, btcec.S256().N).Bytes()
  	x2 := [32]byte{}
  	copy(x2[32-len(x):], x)
  	return x2[:]
  }
docs: // modular big endian addition