change TT size to be a prime number

JonathanArns · Dec 16, 2022 · 5c555c1 · 5c555c1
1 parent 43fabe3
commit 5c555c1
Showing 1 changed file with 2 additions and 3 deletions.
diff --git a/src/minimax/ttable.rs b/src/minimax/ttable.rs
@@ -4,8 +4,7 @@ use std::hash::{Hash, Hasher};
 use std::sync::Mutex;
 use fxhash::FxHasher64;
 
-const TT_LENGTH: usize = 0b_1000000000000000000000000000000;
-const TT_MASK: u64 =     0b__111111111111111111111111111111;
+const TT_LENGTH: usize = 12582917; // prime
 const MAX_SIMUL_GAMES: usize = 1;
 
 /// The transposition table of this battlesnake.
@@ -59,7 +58,7 @@ pub fn get_tt_id(game_id: String) -> u8 {
 }
 
 fn index(tt_id: u8, key: u64) -> usize {
-    tt_id as usize * TT_LENGTH + (key & TT_MASK) as usize
+    tt_id as usize * TT_LENGTH + (key % TT_LENGTH as u64) as usize
 }
 
 /// Get an entry from the transposition table