ecies: use align_num value (#12139)

Co-authored-by: DaniPopes <[email protected]>

crates/net/ecies/src/algorithm.rs

@@ -688,7 +688,7 @@ impl ECIES {
 
     pub fn body_len(&self) -> usize {
         let len = self.body_size.unwrap();
-        (if len % 16 == 0 { len } else { (len / 16 + 1) * 16 }) + 16
+        Self::align_16(len) + 16
     }
 
     #[cfg(test)]
@@ -699,7 +699,7 @@ impl ECIES {
     }
 
     pub fn write_body(&mut self, out: &mut BytesMut, data: &[u8]) {
-        let len = if data.len() % 16 == 0 { data.len() } else { (data.len() / 16 + 1) * 16 };
+        let len = Self::align_16(data.len());
         let old_len = out.len();
         out.resize(old_len + len, 0);
 
@@ -732,6 +732,14 @@ impl ECIES {
         self.ingress_aes.as_mut().unwrap().apply_keystream(ret);
         Ok(split_at_mut(ret, size)?.0)
     }
+
+    /// Returns `num` aligned to 16.
+    ///
+    /// `<https://stackoverflow.com/questions/14561402/how-is-this-size-alignment-working>`
+    #[inline]
+    const fn align_16(num: usize) -> usize {
+        (num + (16 - 1)) & !(16 - 1)
+    }
 }
 
 #[cfg(test)]