fix promotion iterator

src/position.rs

@@ -1087,9 +1087,9 @@ impl MoveGen<Infallible> for MateMoveGenImpl {
 }
 
 struct MoveAndPromote<I: Iterator<Item = RawMove> + ExactSizeIterator + FusedIterator> {
+    role: u8,
     inner: I,
     cur: std::mem::MaybeUninit<RawMove>,
-    role: Role,
 }
 impl<I> MoveAndPromote<I>
 where
@@ -1098,9 +1098,9 @@ where
     #[inline]
     fn new(inner: I) -> Self {
         Self {
+            role: 1,
             inner,
             cur: std::mem::MaybeUninit::uninit(),
-            role: Role::King,
         }
     }
 }
@@ -1111,16 +1111,16 @@ where
     type Item = RawMove;
     #[inline]
     fn next(&mut self) -> Option<RawMove> {
-        if self.role == Role::King {
+        if self.role == 1 {
             self.cur.write(self.inner.next()?);
-            self.role = Role::Knight;
+            self.role = 5;
         }
         let raw = unsafe { self.cur.assume_init() };
         let res = RawMove {
-            role: self.role,
+            role: unsafe { Role::transmute(self.role) },
             ..raw
         };
-        self.role = unsafe { Role::transmute((self.role as u8).unchecked_add(1)) };
+        self.role = unsafe { self.role.unchecked_sub(1) };
         Some(res)
     }
     #[inline]
@@ -1139,6 +1139,6 @@ where
 {
     #[inline]
     fn len(&self) -> usize {
-        unsafe { self.inner.len().unchecked_mul(4) }
+        self.inner.len() * 4 + self.role as usize - 1
     }
 }