refactor: removed branch from mate score adjustment code & put it int…

…o it's own function

bench: 8515103

src/score.rs

@@ -119,10 +119,12 @@ impl Score {
         Self(self.0.abs())
     }
 
-    /// Returns the sign of this [`Score`].
+    /// If this [`Score`] is a mate score, adjust it by 1 to propagate up the search tree.
+    ///
+    /// This helps with mate score adjustments, ensuring that a mate score is always relative to the current ply.
     #[inline(always)]
-    pub const fn signum(self) -> Self {
-        Self(self.0.signum())
+    pub const fn adjust_mate(&mut self) {
+        self.0 -= self.0.signum() * self.is_mate() as i32
     }
 
     /// "Normalizes" a score so that it can be printed as a float.

src/search.rs

@@ -1083,9 +1083,7 @@ impl<'a, Log: LogLevel, V: Variant> Search<'a, Log, V> {
         }
 
         // Adjust mate score by 1 ply, since we're returning up the call stack
-        if best.is_mate() {
-            best -= best.signum();
-        }
+        best.adjust_mate();
 
         // Save this node to the TTable.
         self.save_to_tt(
@@ -1225,9 +1223,7 @@ impl<'a, Log: LogLevel, V: Variant> Search<'a, Log, V> {
         }
 
         // Adjust mate score by 1 ply, since we're returning up the call stack
-        if best.is_mate() {
-            best -= best.signum();
-        }
+        best.adjust_mate();
 
         // Save this node to the TTable.
         self.save_to_tt(