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[3/6] Add MVV-LVA capture ordering and killer moves heuristic #35

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[3/6] Add MVV-LVA capture ordering and killer moves heuristic #35

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@luccabb luccabb commented Jan 20, 2026

Summary

  • Sort captures by MVV-LVA (Most Valuable Victim - Least Valuable Attacker)
  • Add killer moves heuristic for quiet move ordering
  • Track quiet moves that cause beta cutoffs (2 per ply)

Details

MVV-LVA Capture Ordering

Captures are now sorted by MVV-LVA score, putting the best captures first:

  • Taking a queen with a pawn is searched before taking a pawn with a queen
  • Increases the rate of beta cutoffs, reducing nodes searched

Killer Moves Heuristic

Quiet moves that caused beta cutoffs are remembered:

  • Each ply depth keeps track of 2 killer moves
  • Killers are searched immediately after captures
  • Helps find refutation moves faster in similar positions

Move Ordering Priority

  1. Captures - sorted by MVV-LVA
  2. Killer moves - quiet moves that caused cutoffs at this ply
  3. Other quiet moves - shuffled for variety

Test plan

  • All 64 unit tests pass
  • Verified killer moves are updated on beta cutoffs

🤖 Generated with Claude Code

@luccabb luccabb force-pushed the feature/quiescence-search-improvements branch from e8b9ff6 to df8a32b Compare January 21, 2026 06:40
@luccabb luccabb force-pushed the feature/mvv-lva-killer-moves branch from 0b53062 to 944a0e0 Compare January 21, 2026 06:40
@luccabb luccabb force-pushed the feature/quiescence-search-improvements branch from df8a32b to bfb11c1 Compare January 21, 2026 06:44
@luccabb luccabb force-pushed the feature/mvv-lva-killer-moves branch from 944a0e0 to f1001bf Compare January 21, 2026 06:44
@luccabb luccabb changed the base branch from feature/quiescence-search-improvements to feature/transposition-table-bounds January 21, 2026 07:00
@luccabb luccabb changed the title [5/9] Add MVV-LVA capture ordering and killer moves heuristic [3/7] Add MVV-LVA capture ordering and killer moves heuristic Jan 21, 2026
@luccabb luccabb force-pushed the feature/transposition-table-bounds branch from 4f7fad5 to 1c7b8d9 Compare January 21, 2026 07:33
luccabb and others added 2 commits January 20, 2026 23:33
@luccabb @claude
[4/9] Improve quiescence search
c4c327d 
Enhances quiescence search with better handling of special positions:

**Draw Detection:**
- Check fifty-move rule and insufficient material
- Detect repetitions when making moves (return 0 for draws)

**Check Handling:**
- When in check, search ALL legal moves (evasions), not just captures
- Can't use stand-pat for pruning when in check (position is unstable)
- Separate best_score tracking for in-check vs normal positions

**Tactical Move Detection:**
- Add `is_tactical_move()` helper function
- Tactical moves: captures, promotions, and checks
- Previously included quiet pawn pushes (is_zeroing), now more precise

**Move Ordering:**
- Update `organize_moves_quiescence()` to use is_tactical_move
- Sort tactical moves by MVV-LVA

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
@luccabb @claude
[5/9] Add MVV-LVA capture ordering and killer moves heuristic
98ee9e1 
Improves move ordering for better pruning:

**MVV-LVA (Most Valuable Victim - Least Valuable Attacker):**
- Sort captures by MVV-LVA score in `organize_moves()`
- Best captures (e.g., pawn takes queen) searched first
- Increases beta cutoff rate for better pruning

**Killer Moves Heuristic:**
- Track quiet moves that cause beta cutoffs (2 per ply)
- Add `killers` parameter to `organize_moves()` and `negamax()`
- Killer moves searched after captures, before other quiet moves
- Killers stored in a table indexed by ply depth

**Move Ordering Priority:**
1. Captures (sorted by MVV-LVA)
2. Killer moves (quiet moves that caused cutoffs at this ply)
3. Other quiet moves (shuffled for variety)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
@luccabb luccabb force-pushed the feature/mvv-lva-killer-moves branch from f1001bf to 98ee9e1 Compare January 21, 2026 07:33
@luccabb luccabb changed the title [3/7] Add MVV-LVA capture ordering and killer moves heuristic [3/6] Add MVV-LVA capture ordering and killer moves heuristic Jan 21, 2026
@luccabb luccabb mentioned this pull request Jan 27, 2026
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@luccabb luccabb closed this Jan 27, 2026
@luccabb luccabb reopened this Jan 27, 2026
@luccabb luccabb changed the base branch from feature/transposition-table-bounds to master January 27, 2026 19:32
@luccabb luccabb changed the base branch from master to feature/transposition-table-bounds January 27, 2026 19:34
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github-actions bot commented Jan 27, 2026

🔬 Stockfish Benchmark Results

vs Stockfish Skill Level 3

Metric Wins Losses Draws Total Win %
Overall 14 85 1 100 14.0%
As White 7 42 1 50 14.0%
As Black 7 43 0 50 14.0%

Non-checkmate endings:

  • Draw by 3-fold repetition: 1

vs Stockfish Skill Level 4

Metric Wins Losses Draws Total Win %
Overall 12 85 3 100 12.0%
As White 7 42 1 50 14.0%
As Black 5 43 2 50 10.0%

Non-checkmate endings:

  • Draw by insufficient mating material: 1
  • Draw by 3-fold repetition: 1

vs Stockfish Skill Level 5

Metric Wins Losses Draws Total Win %
Overall 2 97 1 100 2.0%
As White 2 47 1 50 4.0%
As Black 0 50 0 50 0%

Non-checkmate endings:

  • Draw by insufficient mating material: 1
Configuration
  • 5 chunks × 20 rounds × 3 skill levels = 300 total games
  • Each opening played with colors reversed (-repeat) for fairness
  • Moonfish: 60s per move
  • Stockfish: 60+5 time control

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github-actions bot commented Jan 27, 2026

🔬 Stockfish Benchmark Results

vs Stockfish Skill Level 3

Metric Wins Losses Draws Total Win %
Overall 7 91 2 100 7.0%
As White 6 42 2 50 12.0%
As Black 1 49 0 50 2.0%

Non-checkmate endings:

  • Draw by fifty moves rule: 1
  • Draw by 3-fold repetition: 1

vs Stockfish Skill Level 4

Metric Wins Losses Draws Total Win %
Overall 11 86 3 100 11.0%
As White 7 41 2 50 14.0%
As Black 4 45 1 50 8.0%

Non-checkmate endings:

  • Draw by 3-fold repetition: 2

vs Stockfish Skill Level 5

Metric Wins Losses Draws Total Win %
Overall 2 96 2 100 2.0%
As White 1 48 1 50 2.0%
As Black 1 48 1 50 2.0%

Non-checkmate endings:

  • Draw by fifty moves rule: 1
  • Draw by 3-fold repetition: 1
Configuration
  • 5 chunks × 20 rounds × 3 skill levels = 300 total games
  • Each opening played with colors reversed (-repeat) for fairness
  • Moonfish: 60s per move
  • Stockfish: 60+5 time control

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@luccabb