From 7a7e7f3665a1c902ce1dfeb32a2c4da2537856c4 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sat, 16 Jul 2022 14:34:46 +0200
Subject: [PATCH] Add 'Rank::{up,down}'

---
 src/board/rank.rs | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/src/board/rank.rs b/src/board/rank.rs
index 11ba5e8..c2499d7 100644
--- a/src/board/rank.rs
+++ b/src/board/rank.rs
@@ -54,6 +54,18 @@ impl Rank {
         self as usize
     }
 
+    /// Return the [Rank] one-row up, as seen from white's perspective. Wraps around the board.
+    pub fn up(self) -> Self {
+        // SAFETY: we know the value is in-bounds, through masking
+        unsafe { Self::from_index_unchecked(self.index().wrapping_add(1) & 7) }
+    }
+
+    /// Return the [Rank] one-row down, as seen from white's perspective. Wraps around the board.
+    pub fn down(self) -> Self {
+        // SAFETY: we know the value is in-bounds, through masking
+        unsafe { Self::from_index_unchecked(self.index().wrapping_sub(1) & 7) }
+    }
+
     /// Turn a [Rank] into a [Bitboard] of all squares in that rank.
     #[inline(always)]
     pub fn into_bitboard(self) -> Bitboard {
@@ -80,6 +92,20 @@ mod test {
         assert_eq!(Rank::Eighth.index(), 7);
     }
 
+    #[test]
+    fn up() {
+        assert_eq!(Rank::First.up(), Rank::Second);
+        assert_eq!(Rank::Second.up(), Rank::Third);
+        assert_eq!(Rank::Eighth.up(), Rank::First);
+    }
+
+    #[test]
+    fn down() {
+        assert_eq!(Rank::First.down(), Rank::Eighth);
+        assert_eq!(Rank::Second.down(), Rank::First);
+        assert_eq!(Rank::Eighth.down(), Rank::Seventh);
+    }
+
     #[test]
     fn into_bitboard() {
         assert_eq!(Rank::First.into_bitboard(), Bitboard::RANKS[0]);