Iron Phoenix

Iron Phoenix is a C++ chess engine built for 4-Player Chess Teams. The engine is designed around a fast mailbox board representation, team-based evaluation, alpha-beta search, transposition tables, and modern move-ordering techniques.

Overview

Iron Phoenix is not a standard 2-player chess engine. It is built specifically for 4-player chess teams, where:

• Red and Yellow are teammates.
• Blue and Green are teammates.
• Turn order is Red → Blue → Yellow → Green.
• The search evaluates positions from the current side’s team perspective.

The goal of the project is to build a strong, fast, and scalable 4PC Teams engine capable of deep search, reliable move ordering, and strong team-aware evaluation.

Featrues

Board Representation

• 14x16 mailbox board
• 224-square internal board
• Invalid mailbox squares for off-board detection
• Fast piece lists by color
• Piece index table for fast add, remove, and move operations
• King square tracking for each color

Supported Colors and Teams

Red = 1 Blue = 2 Yellow = 3 Green = 4

Team RY = Red + Yellow Team BG = Blue + Green

Move Generation

Iron Phoenix currently supports:

• Pawns
• Knights
• Bishops
• Rooks
• Queens
• Kings
• Promotions
• Captures
• Castling
• En passant
• Team-aware legality
• No same-team captures
• Legal move filtering using king safety

Search

Iron Phoenix uses a negamax alpha-beta search designed for 4PC Teams.

Current search features include:

• Iterative deepening
• Alpha-beta pruning
• Quiescence search
• Transposition table probing
• Transposition table storing
• Principal variation tracking
• Time-controlled search using go movetime
• Depth-controlled search using go depth

Move Ordering

Move ordering currently includes:

• Transposition table move
• Captures
• Promotions
• Killer moves
• Quiet move history
• Capture history

The intended ordering priority is:

1. TT move
2. Strong captures
3. Promotions
4. Killer moves
5. Quiet history moves
6. Remaining quiet moves

Evaluation

The evaluation is team-relative.

Iron Phoenix evaluates positions from the perspective of the side to move’s team.

Current evaluation terms include:

Material Mobility Team mobility difference

Example idea:

score > 0  means good for the current side’s team
score < 0  means good for the enemy team

This allows normal negamax sign flipping to work because turn order alternates between teams.

Zobrist Hashing

Iron Phoenix uses Zobrist hashing for fast position keys.

Hash components:

• Piece color
• Piece type
• Square
• Side to move

Important:

initZobrist();

must be called before pieces are added to the board.

Recommended initialization order:

initZobrist();

Position pos;
initStartPosition(pos);

initPawnInfo();
initKnightInfo(pos);
initKingInfo(pos);

pos.key = computeZobristKey(pos);

UCI-Like Commands

Iron Phoenix supports a simple UCI-style command loop.

Engine Setup

uci
isready
ucinewgame
Position Setup
position startpos
position startpos moves h2h3 b11b10

Search:

Search to a fixed depth:

go depth 5

Search for a fixed amount of time:

go movetime 10000

This searches for approximately 10 seconds.

Board Display

d

Perft

perft 4
divide 4
perftdebug 4

Quit

quit