Manually implement Ord according to CAN bus arbitration rules

Author: usbalbin

src/can/id.rs

@@ -1,7 +1,7 @@
 //! CAN Identifiers.
 
 /// Standard 11-bit CAN Identifier (`0..=0x7FF`).
-#[derive(Debug, Copy, Clone, Eq, PartialEq, PartialOrd, Ord, Hash)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq, PartialOrd, Hash)]
 pub struct StandardId(u16);
 
 impl StandardId {
@@ -39,8 +39,15 @@ impl StandardId {
     }
 }
 
+/// Note that this compares as `StandardId::MAX < StandardId::ZERO`
+impl Ord for StandardId {
+    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
+        other.0.cmp(&self.0)
+    }
+}
+
 /// Extended 29-bit CAN Identifier (`0..=1FFF_FFFF`).
-#[derive(Debug, Copy, Clone, Eq, PartialEq, PartialOrd, Ord, Hash)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq, PartialOrd, Hash)]
 pub struct ExtendedId(u32);
 
 impl ExtendedId {
@@ -84,6 +91,13 @@ impl ExtendedId {
     }
 }
 
+/// Note that this compares as `ExtendedId::MAX < ExtendedId::ZERO`
+impl Ord for ExtendedId {
+    fn cmp(&self, other: &Self) -> core::cmp::Ordering {
+        other.0.cmp(&self.0)
+    }
+}
+
 /// A CAN Identifier (standard or extended).
 #[derive(Debug, Copy, Clone, Eq, PartialEq, PartialOrd, Ord, Hash)]
 pub enum Id {
@@ -157,4 +171,20 @@ mod tests {
             StandardId::new((ExtendedId::MAX.0 >> 18) as u16)
         );
     }
+
+    #[test]
+    fn cmp_standard() {
+        assert!(StandardId::MAX < StandardId::ZERO);
+    }
+
+    #[test]
+    fn cmp_extended() {
+        assert!(ExtendedId::MAX < ExtendedId::ZERO);
+    }
+
+    #[test]
+    fn cmp_id() {
+        assert!(Id::Standard(StandardId::MAX) < Id::Standard(StandardId::ZERO));
+        assert!(Id::Extended(ExtendedId::MAX) < Id::Extended(ExtendedId::ZERO));
+    }
 }