factor this out

1 files changed, 10 insertions, 8 deletions

diff --git a/src/aes.rs b/src/aes.rs
index b3aa71c..5caaca1 100644
--- a/src/aes.rs
+++ b/src/aes.rs
@@ -249,14 +249,9 @@ fn find_block_size<F> (f: &F) -> usize where F: Fn(&[u8]) -> Vec<u8> {
             .collect();
         let next = f(&prefix[..]);
 
-        let shared_prefix_len = prev
-            .iter()
-            .enumerate()
-            .take_while(|&(i, &c)| { c == next[i] })
-            .count();
-
-        if shared_prefix_len > 0 {
-            return shared_prefix_len;
+        let prefix_len = shared_prefix_len(prev.iter(), next.iter());
+        if prefix_len > 0 {
+            return prefix_len;
         }
 
         prev = next;
@@ -264,6 +259,13 @@ fn find_block_size<F> (f: &F) -> usize where F: Fn(&[u8]) -> Vec<u8> {
     }
 }
 
+fn shared_prefix_len<I> (i1: I, i2: I) -> usize where I: Iterator, <I as Iterator>::Item: PartialEq {
+    return i1
+        .zip(i2)
+        .take_while(|&(ref c1, ref c2)| { c1 == c2 })
+        .count();
+}
+
 #[test]
 fn test_encrypt_decrypt () {
     let plaintext = b"Summertime and the wind is blowing outside in lower \