analog-hors / Cheers

UCI chess engine written in Rust

Cheers - a UCI chess engine written in Rust

Cheers is not a complete chess program and should be used in conjunction with a UCI frontend e.g. Cute Chess.

Options

Currently supported options are:

• Hash: Default: 32, Minimum: 1, Maximum: 32768
  Transposition table size in megabytes.
• Threads Default: 1, Minimum: 1, Maximum: 256
  The number of thread to search with.
• NmpDepth: Default: 1, Minimum: 1, Maximum: 10
  The depth above which Null Move Pruning is applied.
• NmpConstReduction: Default: 3, Minimum: 1, Maximum: 10
  The constant reduction to apply to all Null Move Pruning.
• NmpLinearDivisor: Default: 3, Minimum: 1, Maximum: 10
  The divisor applied to the depth in Null Move Pruning. The general formula is reduction = NmpConstReduction + (depth / NmpLinearDivisor).
• SeePruningDepth: Default: 6, Minimum: 1, Maximum: 10
  The depth below which SEE Pruning is applied.
• SeeCaptureMargin: Default: -30, Minimum: -200, Maximum: 200
  The margin around beta where SEE Pruning is accepted for captures.
• SeeQuietMargin: Default: -98, Minimum: -100, Maximum: -100
  The margin around beta where SEE Pruning is accepted for quiet moves.
• PvsFullDepth: Default: 2, Minimum: 1, Maximum: 5
  The depth at which all moves are searched without reductions.
• DeltaPruningMargin: Default: 91, Miniimum: 0, Maximum: 300
  The margin around beta where Delta Pruning is accepted.
• FpMargin1: Default: 162, Minimum: 0, Maximum: 300
  The margin around alpha where Futility Pruning is accepted at depth 1.
• FpMargin2: Default: 320, Minimum: 0, Maximum: 700
  The margin around alpha where Futility Pruning is accepted at depth 2.
• FpMargin3: Default: 706, Minimum: 500, Maximum: 1000
  The margin around alpha where Futility Pruning is accepted at depth 3.
• RfpMargin: Default: 140, Minimum: 0, Maximum: 300
  The margin around beta where Reverse Futility Pruning is accepted.
• LmpDepth: Default: 2, Minimum: 0, Maximum: 10
  The depth at or below which Late Move Pruning is applied
• LmpMargin: Default: 6, Minimum: 1, Maximum: 15
  The quadratic coefficient with depth. After LmpMargin * depth*depth moves pruning can be applied.
• IirDepth: Default: 6, Minimum: 2, Maximum: 10
  The depth above which Internal Iterative Reduction is applied.

Features (in no particular order)

General

• Magic Bitboard board representation
• Legal move generation

Search

• Multithreading with Lazy SMP
• Iterative Deeping
• Transposition Table
• Aspiration Windows
• Principal Variation Alpha-Beta search
• Null Move Pruning
• Late Move Reduction
• Late Move Pruning
• Futility Pruning
• Reverse Futility Pruning
• Internal Iterative Reduction
• Static Exchange Evaluation Pruning
• Mate Distance Pruning

Quiescence Search

• Transposition Table
• Delta Pruning
• Static Exchange Evaluation Pruning

Move Ordering

• Hash move from transposition table
• MVV-LVA ordering on captures
• Queen promotions
• Killer Move Heuristic
• Counter Move Heuristic
• History Heuristic

Evaluation

Cheers currently uses a hand-crafted evaluation function with Texel-tuned parameters. NNUE is planned for the future.

General

• Tapered Evaluation
• Pawn Hash Table (8MB)

Pawns

• Material
• Piece-Square Tables
• Doubled Pawn
• Isolated Pawn
• Connected Pawn
• Passed Pawn
• Passed Pawn Rank
• Passed Pawn Blocked
• Passed Pawn Connected
• Passed Pawn Supported by Rook
• Passed Pawn Uncatchable by enemy King

Knights

• Material
• Piece-Square Tables
• Mobility
• Knight behind Pawn
• Knight distance from friendly King
• Knight on (defended) outpost

Bishops

• Material
• Piece-Square Tables
• Mobility
• Bishop behind Pawn
• Bishop distance from friendly King
• Bishop on (defended) outpost
• Bishop Pair
• Bishop on long diagonal

Rooks

• Material
• Piece-Square Tables
• Mobility
• Rook on (semi) open file
• Rook on seventh rank
• Rook trapped by friendly King

Queens

• Material
• Piece-Square Tables
• Mobility
• Risk of discovered attack

Kings

• Piece-Square Tables
• Mobility
• Minor piece defenders
• King on open file