Implement bit-fields.

tests/bit_shift.rs

@@ -13,3 +13,38 @@ fn test_right_shift() -> Result<(), Box<EvalAltResult>> {
     assert_eq!(engine.eval::<INT>("9 >> 1")?, 4);
     Ok(())
 }
+
+#[cfg(not(feature = "no_index"))]
+#[test]
+fn test_bit_fields() -> Result<(), Box<EvalAltResult>> {
+    let engine = Engine::new();
+    assert!(!engine.eval::<bool>("let x = 10; x[0]")?);
+    assert!(engine.eval::<bool>("let x = 10; x[1]")?);
+    assert!(!engine.eval::<bool>("let x = 10; x[-1]")?);
+    assert_eq!(
+        engine.eval::<INT>("let x = 10; x[0] = true; x[1] = false; x")?,
+        9
+    );
+    assert_eq!(engine.eval::<INT>("let x = 10; get_bits(x, 1, 3)")?, 5);
+    assert_eq!(
+        engine.eval::<INT>("let x = 10; set_bits(x, 1, 3, 7); x")?,
+        14
+    );
+    assert_eq!(
+        engine.eval::<INT>(
+            "
+                let x = 0b001101101010001;
+                let count = 0;
+
+                for b in bits(x, 2, 10) {
+                    if b { count += 1; }
+                }
+
+                count
+            "
+        )?,
+        5
+    );
+
+    Ok(())
+}