Did you know that the piece with the lowest survival rate is the white queen’s pawn at d2? That’s right, out of 2.2 million master level games, this pawn survives the least games at only 24.5%. Conversely, king not withstanding, the one piece with the highest survival rate of any of those games is the white king’s rook’s pawn at h2? It survives over 73% of games played! With such a wild spectrum, this small piece is actually the highest and lowest survivor of any chess game. You can check out all of the stats for piece survival here at Oliver’s blog.
Of special interest, Oliver also wrote a program to analyse all of the moves to find that information, which you can look at on GitHub.
Personally, I find the pawn to be the most important piece of the game. But that is for another time. For now, we need to make some pawn moves. Surprisingly, for such a simple piece, it has the most complicated moves:
- Pawns can move forward one space.
- Pawns can move forward two spaces from the “home” row.
- Pawns can attack diagonally forward.
- Pawns can perform en passant only under the right conditions.
- Pawns can promote to another piece.
I am sure that you realized those moves exist, but by seeing them put to paper we can really get the feel for how complicated making the pawn move is! Of all of those moves, 4 of the 5 are conditional, meaning they can only be done under certain conditions. This makes programming them tough, as you have to check if those conditions exist, then check if making the move is possible, then check if that move is safe for the king.
As you can see in my pawn commit, I added the pawn moves, but there are some flaws in them. Unfortunately, most of these flaws were not realized at the time, but were fixed later, here and here. Essentially, the move that was flawed is en passant, both in the making and the undoing of that move. However, I did not realize it at this point, until I started making the engine perform and undo moves.
So, take a look at the code, and feel free to comment if you think of a better way to do those moves.
Linux – keep it simple.