Make SipHasher128::finish non-fatal by returning a small-hash

Author: Urgau

src/sip128.rs

@@ -503,7 +503,11 @@ impl Hasher for SipHasher128 {
     }
 
     fn finish(&self) -> u64 {
-        panic!("SipHasher128 cannot provide valid 64 bit hashes")
+        let mut buf = self.buf.clone();
+        let [a, b] = SipHasher128::finish128_inner(self.nbuf, &mut buf, self.state, self.processed);
+
+        // Combining the two halves makes sure we get a good quality hash.
+        a.wrapping_mul(3).wrapping_add(b).to_le()
     }
 }
 

src/sip128/tests.rs

@@ -303,3 +303,13 @@ fn test_fill_buffer() {
     test_fill_buffer!(i128, write_i128);
     test_fill_buffer!(isize, write_isize);
 }
+
+#[test]
+fn test_finish() {
+    let mut hasher = SipHasher128::new_with_keys(0, 0);
+
+    hasher.write_isize(0xF0);
+    hasher.write_isize(0xF0010);
+
+    assert_eq!(hasher.finish(), hasher.finish());
+}