code: func (curve *KoblitzCurve) bigAffineToField(x, y *big.Int) (*fieldVal, *fieldVal) {
  	x3, y3 := new(fieldVal), new(fieldVal)
  	x3.SetByteSlice(x.Bytes())
  	y3.SetByteSlice(y.Bytes())
  
  	return x3, y3
  }
docs: // bigAffineToField takes an affine point (x, y) as big integers and converts
  // it to an affine point as field values.