refactor: exponentially grow windows on research

1 files changed, 9 insertions, 7 deletions

diff --git a/src/board/engine.rs b/src/board/engine.rs
index 35aec11..8809378 100644
--- a/src/board/engine.rs
+++ b/src/board/engine.rs
@@ -323,7 +323,9 @@ impl Board {
         }
 
         if principal_variation.len() == 0 {
-            return (-VALUE_WIN, principal_variation);
+            if self.is_king_in_check(color) {
+                return (-VALUE_WIN, principal_variation);
+            }
         }
 
         (alpha, principal_variation)
@@ -382,7 +384,7 @@ 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
+        let mut gradual_widening_counter = 0;
 
         while depth <= max_depth {
             let search_result = self.negamax_search(alpha, beta, depth, deadline);
@@ -397,20 +399,20 @@ impl Board {
             }
             if search_result.1.len() > 0 {
                 depth += 1;
-                gradual_widening_multiplier = 1.0;
+                gradual_widening_counter = 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;
+                gradual_widening_counter += 1;
                 beta = alpha;
-                alpha = search_result.0 - window_size * gradual_widening_multiplier;
+                alpha = search_result.0 - window_size * 4.0f32.powi(gradual_widening_counter);
                 continue;
             } else if search_result.0 >= beta { // Beta-cutoff
                 println!("Beta cutoff {:?} <= {}", (alpha, beta), search_result.0);
-                gradual_widening_multiplier *= 4.0;
+                gradual_widening_counter += 1;
                 alpha = beta;
-                beta = search_result.0 + window_size * gradual_widening_multiplier;
+                beta = search_result.0 + window_size * 4.0f32.powi(gradual_widening_counter);
                 continue;
             } else {
                 panic!("Can this ever be possible? (probably not)");