feat: prioritize checkmate branches

1 files changed, 16 insertions, 2 deletions

diff --git a/src/board/engine.rs b/src/board/engine.rs
index 53d2564..35aec11 100644
--- a/src/board/engine.rs
+++ b/src/board/engine.rs
@@ -5,6 +5,8 @@ use super::ttable::{NodeType, TranspositionTableItem};
 
 static A_FILE:     Bitboard = 0x0101010101010101;
 
+const VALUE_WIN: f32 = 20_000.0;
+
 #[derive(Debug, Default, PartialEq)]
 pub struct PerftResult {
     leaf_nodes: u64,
@@ -320,6 +322,10 @@ impl Board {
             }
         }
 
+        if principal_variation.len() == 0 {
+            return (-VALUE_WIN, principal_variation);
+        }
+
         (alpha, principal_variation)
     }
 
@@ -376,27 +382,35 @@ impl Board {
         let mut alpha = -INFINITY;
         let mut beta = INFINITY;
         let window_size = 0.25;
+        let mut gradual_widening_multiplier = 1.0; // Grows on cutoffs
 
         while depth <= max_depth {
             let search_result = self.negamax_search(alpha, beta, depth, deadline);
             println!("Finished depth({}) {:?} [{:?} left]", depth, search_result, deadline - Instant::now());
 
+            if search_result.0.abs() >= VALUE_WIN {
+                return search_result
+            }
+
             if Instant::now() > deadline {
                 break;
             }
             if search_result.1.len() > 0 {
                 depth += 1;
+                gradual_widening_multiplier = 1.0;
                 alpha = search_result.0 - window_size;
                 beta = search_result.0 + window_size;
             } else if search_result.0 <= alpha { // Alpha-cutoff
                 println!("Alpha cutoff {} <= {:?}", search_result.0, (alpha, beta));
+                gradual_widening_multiplier *= 4.0;
                 beta = alpha;
-                alpha = search_result.0 - window_size * 4.0;
+                alpha = search_result.0 - window_size * gradual_widening_multiplier;
                 continue;
             } else if search_result.0 >= beta { // Beta-cutoff
                 println!("Beta cutoff {:?} <= {}", (alpha, beta), search_result.0);
+                gradual_widening_multiplier *= 4.0;
                 alpha = beta;
-                beta = search_result.0 + window_size * 4.0;
+                beta = search_result.0 + window_size * gradual_widening_multiplier;
                 continue;
             } else {
                 panic!("Can this ever be possible? (probably not)");