chess-cpp

TLDR: Don't waste your time by looking here.

Source code (C++98) for the program made in my master thesis: Generation and compression of endgame tables in chess with fast random access using OBDDs.

More information is available here (hasn't been updated for a long time).

Bugs

When I wrote this program I made use of several optimizations that were based on how the compiler I was using happened to behave. In some cases this was a deliberate (but bad) choice. In most cases I didn't know better.

These are some of the mistakes that I've been hit by:

• I assumed that a char was an unsigned 8 bit integer.
• I assumed that I could write to one union member and read the corresponding bits from another union member

A few times I've tried to rectify the errors and make the program work again. But this is hard work with 35k lines of poorly documented code :-/

Currently large parts of it is working (in a dockerized build environment) but there are still significant problems.

Known bugs

• Some short versions of commands causes crash (e.g. "ctfi ..." instead of "construct from table index ...")
• With retrograde construction many (all?) invalid positions are stored as draw (-125) instead of illegal (-128). This reduces how much the tables can be compressed as OBDDs.
• The 5 piece KPPKP endgame cannot be constructed as it contains a position with a depth to mate of 127 (8/8/8/8/1p2P3/4P3/1k6/3K4 w - - 0 1). This cannot fit in the uint8_t as values -124 and below are reserved.
• When compiled against XBoard an error is logged when quitting the program (free(): double free detected in tcache 2)
• Retrograde construction of KBNKP fails for a position with a pawn at an invalid square:

Error: Retrograde constr.: Player from index = 9217
(it is 1 to move)
Num checks = 0
    a b c d e f g h
  +-----------------+    |
8 |                 | 8  | 50b
7 |                 | 7  |
6 |                 | 6  | White has lost castling
5 |                 | 5  | Black has lost castling
4 |                 | 4  |
3 |                 | 3  | moves played since progress = 0
2 | N               | 2  |
1 | k p K B         | 1  |
  +-----------------+    |
    a b c d e f g h
FEN: loadfen 8/8/8/8/8/8/N7/kpKB4 b - - 0 50

What seems to work

• The endgames tables that are built seems to be correct. At least they are correct for some longest mates for 5 piece endgames (test.com)
• The chess engine can be used by xboard (tested with version 4.9.1). As command use make run_xb using the root of this repository as folder. This assumes you have docker installed. Maybe you should run make run_xb first to prebuild the image.