From e6a51b1dc32e9abefbf060d1fa35d1599d6b6374 Mon Sep 17 00:00:00 2001
From: Michal Nazarewicz <mina86@mina86.com>
Date: Sat, 2 Dec 2023 19:27:02 +0100
Subject: [PATCH] =?UTF-8?q?Implement=20BitIdx=20=E2=86=92=20BitEnd=20conve?=
 =?UTF-8?q?rsion?=
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Since BitIdx’s inner value is always withing the domain of BigEnd type
it is theoretically possible to convert infallibly the former into the
latter.  Alas, no such facility exist and instead conversion through
u8 is required.

Introduce `From<BitIdx<R>> for BitEnd<R>` implementation which
provides that feature.
---
 src/index.rs | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/index.rs b/src/index.rs
index 98f88e4c..061bde46 100644
--- a/src/index.rs
+++ b/src/index.rs
@@ -106,7 +106,6 @@ where R: BitRegister
 
 	/// Removes the index wrapper, leaving the internal counter.
 	#[inline]
-	#[cfg(not(tarpaulin_include))]
 	pub fn into_inner(self) -> u8 {
 		self.idx
 	}
@@ -593,6 +592,14 @@ where R: BitRegister
 	}
 }
 
+impl<R: BitRegister> From<BitIdx<R>> for BitEnd<R> {
+	fn from(idx: BitIdx<R>) -> Self {
+		// SAFETY: Maximum allowed value of BitIdx<R> is always smaller
+		// than maximum allowed value of BitEnd<R>.
+		unsafe { Self::new_unchecked(idx.into_inner()) }
+	}
+}
+
 #[repr(transparent)]
 #[doc = include_str!("../doc/index/BitPos.md")]
 // #[rustc_layout_scalar_valid_range_end(R::BITS)]
@@ -1083,6 +1090,12 @@ mod tests {
 			assert!(BitEnd::<usize>::new(n).is_some());
 		}
 		assert!(BitEnd::<usize>::new(bits_of::<usize>() as u8 + 1).is_none());
+
+		for n in 0 .. bits_of::<usize>() as u8 {
+			let idx = BitIdx::<usize>::new(n).unwrap();
+			let end = BitEnd::<usize>::new(n).unwrap();
+			assert_eq!(end, BitEnd::from(idx));
+		}
 	}
 
 	#[test]