Expose get_diff_ratio

src/algorithms/capture.rs

@@ -247,6 +247,31 @@ pub fn group_diff_ops(mut ops: Vec<DiffOp>, n: usize) -> Vec<Vec<DiffOp>> {
     rv
 }
 
+/// Return a measure of similarity in the range `0..=1`.
+///
+/// A ratio of `1.0` means the two sequences are a complete match, a
+/// ratio of `0.0` would indicate completely distinct sequences.  The input
+/// is the sequence of diff operations and the length of the old and new
+/// sequence.
+pub fn get_diff_ratio(ops: &[DiffOp], old_len: usize, new_len: usize) -> f32 {
+    let matches = ops
+        .iter()
+        .map(|op| {
+            if let DiffOp::Equal { len, .. } = *op {
+                len
+            } else {
+                0
+            }
+        })
+        .sum::<usize>();
+    let len = old_len + new_len;
+    if len == 0 {
+        1.0
+    } else {
+        2.0 * matches as f32 / len as f32
+    }
+}
+
 impl DiffHook for Capture {
     type Error = Infallible;