DRY up unknown_features calculation

Author: tnull

lightning/src/ln/features.rs

@@ -771,15 +771,7 @@ impl<T: sealed::Context> Features<T> {
 		// unknown features.
 		self.flags.iter().enumerate().any(|(i, &byte)| {
 			const REQUIRED_FEATURES: u8 = 0b01_01_01_01;
-			const OPTIONAL_FEATURES: u8 = 0b10_10_10_10;
-			let unknown_features = if i < other.flags.len() {
-				// Form a mask similar to !T::KNOWN_FEATURE_MASK only for `other`
-				!(other.flags[i]
-					| ((other.flags[i] >> 1) & REQUIRED_FEATURES)
-					| ((other.flags[i] << 1) & OPTIONAL_FEATURES))
-			} else {
-				0b11_11_11_11
-			};
+			let unknown_features = self.unknown_features_at_position(other, i);
 			(byte & (REQUIRED_FEATURES & unknown_features)) != 0
 		})
 	}
@@ -790,17 +782,7 @@ impl<T: sealed::Context> Features<T> {
 		// Bitwise AND-ing with all even bits set except for known features will select required
 		// unknown features.
 		self.flags.iter().enumerate().for_each(|(i, &byte)| {
-			const REQUIRED_FEATURES: u8 = 0b01_01_01_01;
-			const OPTIONAL_FEATURES: u8 = 0b10_10_10_10;
-			let unknown_features = if i < other.flags.len() {
-				// Form a mask similar to !T::KNOWN_FEATURE_MASK only for `other`
-				!(other.flags[i]
-					| ((other.flags[i] >> 1) & REQUIRED_FEATURES)
-					| ((other.flags[i] << 1) & OPTIONAL_FEATURES))
-			} else {
-				0b11_11_11_11
-			};
-
+			let unknown_features = self.unknown_features_at_position(other, i);
 			if byte & unknown_features != 0 {
 				for bit in (0..8).step_by(2) {
 					if byte >> bit & 1 == 1 {
@@ -813,6 +795,19 @@ impl<T: sealed::Context> Features<T> {
 		unknown_bits
 	}
 
+	pub(crate) fn unknown_features_at_position(&self, other: &Self, index: usize) -> u8 {
+		const REQUIRED_FEATURES: u8 = 0b01_01_01_01;
+		const OPTIONAL_FEATURES: u8 = 0b10_10_10_10;
+		if index < other.flags.len() {
+			// Form a mask similar to !T::KNOWN_FEATURE_MASK only for `other`
+			!(other.flags[index]
+				| ((other.flags[index] >> 1) & REQUIRED_FEATURES)
+				| ((other.flags[index] << 1) & OPTIONAL_FEATURES))
+		} else {
+			0b11_11_11_11
+		}
+	}
+
 	/// Returns true if this `Features` object contains unknown feature flags which are set as
 	/// "required".
 	pub fn requires_unknown_bits(&self) -> bool {