Fix findLast, add last function for Bitboard

Also add tests

src/main/scala/bitboard/Bitboard.scala

@@ -111,6 +111,7 @@ object Bitboard:
     inline def isDisjoint(o: Bitboard): Boolean =
       (a & o).isEmpty
 
+    // return list of square that sorted ascendingly
     def squares: List[Square] =
       var b       = a
       val builder = List.newBuilder[Square]
@@ -129,6 +130,15 @@ object Bitboard:
         b &= (b - 1L)
       result
 
+    def last[B](f: Square => Option[B]): Option[B] =
+      var b                 = a
+      var result: Option[B] = None
+      while b != 0L && result.isEmpty
+      do
+        result = f(b.msb)
+        b &= ~b.msb.bl
+      result
+
     def find(f: Square => Boolean): Option[Square] =
       var b                      = a
       var result: Option[Square] = None
@@ -138,14 +148,13 @@ object Bitboard:
         b &= (b - 1L)
       result
 
-    // tests
     def findLast(f: Square => Boolean): Option[Square] =
       var b                      = a
       var result: Option[Square] = None
       while b != 0L && result.isEmpty
       do
         if f(b.msb) then result = Some(b.msb)
-        b &= (b - 1L)
+        b &= ~b.msb.bl
       result
 
     def fold[B](init: B)(f: (B, Square) => B): B =

test-kit/src/test/scala/bitboard/BitboardTest.scala

@@ -54,6 +54,27 @@ class BitboardTest extends ScalaCheckSuite:
       def f = (p: Square) => if p == x then Some(p) else None
       Bitboard(xs + x).first(f) == Some(x)
 
+  test("last with a function that always return None should return None"):
+    forAll: (bb: Bitboard) =>
+      assertEquals(bb.last(_ => None), None)
+
+  test("last with a function that always return Some should return the last square"):
+    forAll: (bb: Bitboard) =>
+      assertEquals(bb.last(Some(_)), bb.last)
+
+  test("last returns the correct square"):
+    forAll: (xs: Set[Square], x: Square) =>
+      def f = (p: Square) => if p == x then Some(p) else None
+      Bitboard(xs + x).last(f) == Some(x)
+
+  test("find"):
+    forAll: (bb: Bitboard, f: Square => Boolean) =>
+      bb.find(f) == bb.squares.find(f)
+
+  test("findLast"):
+    forAll: (bb: Bitboard, f: Square => Boolean) =>
+      bb.findLast(f) == bb.squares.reverse.find(f)
+
   test("bitboard created by set of square should contains and only contains those square"):
     forAll: (xs: Set[Square]) =>
       val bb = Bitboard(xs)
@@ -147,6 +168,10 @@ class BitboardTest extends ScalaCheckSuite:
     forAll: (b: Bitboard, f: Square => Option[Int]) =>
       b.first(f) == b.squares.map(f).find(_.isDefined).flatten
 
+  property("last"):
+    forAll: (b: Bitboard, f: Square => Option[Int]) =>
+      b.last(f) == b.squares.map(f).findLast(_.isDefined).flatten
+
   property("foreach"):
     forAll: (b: Bitboard, f: Square => Int) =>
       var s1 = 0L