Based on > How does it work? Here's a hint: the white arrows correspond to 10x mod 7. (which of course is the same as 3x mod 7), it seems that the author inte

Based on > How does it work? Here's a hint: the white arrows correspond to 10x mod 7. (which of course is the same as 3x mod 7), it seems that the author intentionally wants to leave it as a slight puzzle. But blacksqr's suggestion (https://news.ycombinator.com/item?id=27222819 https://news.ycombinator.com/item?id=27222819) to write it yourself is even better!