Merge pull request #594 from lichess-org/discard-least-significant-ha…

…sh-byte throw away lsb rather than msb of position hashes
lichess-org · Nov 6, 2024 · c3774a4 · c3774a4
2 parents 6bf25de + 64c945e
commit c3774a4
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Showing 2 changed files with 3 additions and 3 deletions.
diff --git a/core/src/main/scala/Hash.scala b/core/src/main/scala/Hash.scala
@@ -29,8 +29,8 @@ object PositionHash:
 opaque type Hash = Int
 object Hash:
   val size                              = 3
-  def apply(value: Int): Hash           = value & 0x00ff_ffff
-  def apply(situation: Situation): Hash = hashSituation(situation) & 0x00ff_ffff
+  def apply(value: Int): Hash           = value >>> 8
+  def apply(situation: Situation): Hash = hashSituation(situation) >>> 8
 
   private def hashSituation(situation: Situation): Int =
     import situation.board

diff --git a/test-kit/src/test/scala/HistoryTest.scala b/test-kit/src/test/scala/HistoryTest.scala
@@ -2,7 +2,7 @@ package chess
 
 class ThreefoldRepetitionTest extends ChessTest:
 
-  def toHash(a: Int) = PositionHash(Hash(a))
+  def toHash(a: Int) = PositionHash(Hash(a << 8))
   def makeHistory(positions: List[Int]) =
     (positions
       .map(toHash))