bitfield: add set ratio

src/net/bitfield.rs

@@ -49,6 +49,10 @@ impl BitField {
     pub fn as_bytes(&self) -> &[u8] {
         &self.bits
     }
+
+    pub fn set_ratio(&self) -> f64 {
+        self.bits.iter().map(|b| b.count_ones()).sum::<u32>() as f64 / self.len as f64
+    }
 }
 
 impl fmt::Debug for BitField {
@@ -107,3 +111,10 @@ fn test_bitfield_unset() {
     bf.unset(15);
     assert_eq!(bf.bits[1], 255-128-1);
 }
+
+#[test]
+fn test_bitfield_set_ratio() {
+    use std::f64;
+    let mut bf = BitField::new(vec![255, 255], 16);
+    assert!(f64::abs(bf.set_ratio() - 1.0) < f64::EPSILON);
+}