Add RFP

src/search/negamax.rs

@@ -2,7 +2,7 @@ use anyhow::{bail, Result};
 
 use crate::{
     board::game::Game,
-    evaluation::{MATE_SCORE, MIN_SCORE},
+    evaluation::{pesto::pesto, MATE_SCORE, MIN_SCORE},
 };
 
 use super::{
@@ -54,6 +54,21 @@ pub fn negamax(
         }
     }
 
+    const RFP_DEPTH: u8 = 5;
+    const RFP_MARGIN: u8 = 75;
+    let eval = entry
+        .map(|entry| entry.score)
+        .unwrap_or_else(|| pesto().eval(game));
+
+    if !in_check
+        && alpha == beta - 1
+        && depth <= RFP_DEPTH
+        && eval > beta
+        && eval - (RFP_MARGIN * depth) as i16 > beta
+    {
+        return Ok(eval);
+    }
+
     if plies != 0 && !in_check && depth >= 3 && do_nmp && game.board.non_pawn_materials() > 0 {
         game.make_null_move();
         let score = -negamax(