Lite Blue

A portable chess engine in C89, for AIX and other Unix systems. By DeepSeek (deepseek-v4.1-flash).

Lite Blue is deliberately single-node. It was written for one IBM RS/6000 43P (PowerPC 604e, 250 MHz, AIX 4.3.3) as the small answer to Deep Blue, but it builds unmodified on ordinary Unix.

Features

• 0x88 board representation.
• Negamax alpha-beta search: iterative deepening, a Zobrist transposition table, quiescence search, null-move pruning, late-move reductions, principal-variation search, and killer/history move ordering.
• Hand-tuned evaluation: material, piece-square tables, and a tapered king.
• Three front ends over one library:
  • liteblue - UCI, the authoritative interface.
  • tui - an interactive terminal board.
  • arena - a self-play / match driver.

Build

cd src
make                                                 # cc
make CC=/usr/vac/bin/xlc CFLAGS="-O2 -qlanglvl=ansi" # IBM XL C
make CC=gcc CFLAGS="-O2 -ansi"                       # GCC

Run

UCI:

printf 'position startpos\ngo depth 8\nquit\n' | ./liteblue

Interactive: ./tui (type a move like e2e4, or d, undo, new, go, time <ms>, quit).

Self-play: ./arena 500 40 (500 ms per move, up to 40 plies).

Tools

tools/match plays two engine binaries against each other over UCI and reports the score and an Elo delta; it is how engine changes are measured here.

cd tools && make
./match ../src/liteblue ../src/liteblue 6 6 200

Usage: match ENGINE_A ENGINE_B [depthA] [depthB] [max_plies] [book] [nodes]. Each engine is a persistent UCI process (moves cost only the search); each opening is played twice, colours swapped. book is an optional file of opening positions (one FEN per line, e.g. a UHO subset); without it a small built-in list is used. If nodes is given, engines play go nodes <n> instead of go depth - use it to measure search-efficiency changes, which fixed-depth games do not reward.

Correctness

• Move generation is perft-verified against the standard test positions, with the Zobrist key recomputed and compared at every internal node.
• The search is deterministic across XL C 5.0.2 and GCC 2.95.3 (byte-identical node counts).
• make check runs a repetition regression test and the perft suite.

Measured on the 250 MHz PowerPC 604e: about 47,000 nodes per second.

Version

1.0.0; see CHANGELOG.md. The version lives in src/version.h and is reported over UCI on the id name line.

Licence

MIT. See LICENSE.