returnByte method
Process one byte of data given by inp
and return its encrypted value.
Implementation
@override
int returnByte(int inp) {
_x = (_x + 1) & 0xff;
_y = (_engineState![_x] + _y) & 0xff;
// swap
var tmp = _engineState![_x];
_engineState![_x] = _engineState![_y];
_engineState![_y] = tmp;
// xor
return inp ^ _engineState![(_engineState![_x] + _engineState![_y]) & 0xff];
}