dsa: compare key sizes aligned to limb

This allows to compare key sizes after a back and forth through
serialization which could lose the exact key size.

Author: baloo

dsa/src/size.rs

@@ -1,7 +1,8 @@
+use core::cmp::Ordering;
 use crypto_bigint::Limb;
 
 /// DSA key size
-#[derive(Clone, Debug, Copy, PartialEq, PartialOrd)]
+#[derive(Clone, Debug, Copy)]
 pub struct KeySize {
     /// Bit size of p
     pub(crate) l: u32,
@@ -48,3 +49,18 @@ impl KeySize {
         l == self.l_aligned() && n == self.n_aligned()
     }
 }
+
+impl PartialEq for KeySize {
+    fn eq(&self, other: &Self) -> bool {
+        self.l_aligned() == other.l_aligned() && self.n_aligned() == other.n_aligned()
+    }
+}
+
+impl PartialOrd for KeySize {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        let l = self.l_aligned().partial_cmp(&other.l_aligned())?;
+        let n = self.n_aligned().partial_cmp(&other.n_aligned())?;
+
+        Some(l.then(n))
+    }
+}