DRY up `unknown_features` calculation

diff --git a/lightning/src/ln/features.rs b/lightning/src/ln/features.rs
index 9dcac57888a4dc6416660cb41eef35669dcae8e3..6b4834edf67efdec993aadacfee17376adb65237 100644 (file)
--- a/lightning/src/ln/features.rs
+++ b/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 = unset_features_mask_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 = unset_features_mask_at_position(other, i);
                        if byte & unknown_features != 0 {
                                for bit in (0..8).step_by(2) {
                                        if ((byte & unknown_features) >> bit) & 1 == 1 {
@@ -1047,6 +1029,19 @@ impl<T: sealed::Context> Readable for WithoutLength<Features<T>> {
        }
 }
 
+pub(crate) fn unset_features_mask_at_position<T: sealed::Context>(other: &Features<T>, 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
+       }
+}
+
 #[cfg(test)]
 mod tests {
        use super::{ChannelFeatures, ChannelTypeFeatures, InitFeatures, Bolt11InvoiceFeatures, NodeFeatures, OfferFeatures, sealed};