diff --git a/homework/chapter2/tneg_4.c b/homework/chapter2/tneg_4.c
new file mode 100644
index 0000000..ead1932
--- /dev/null
+++ b/homework/chapter2/tneg_4.c
@@ -0,0 +1,21 @@
+#include <assert.h>
+#include <limits.h>
+
+/*
+* Generate mask indicating rightmost 1 in x.
+* For example 0xFF00 -> 0x0100, and 0x6600 --> 0x0200.
+* If x == 0, then return 0.
+*/
+int rightmost_one(unsigned x) {
+  return x & -x;
+}
+
+int main() {
+  for (unsigned x = 0; ; x++) {
+    assert((x == 0 && rightmost_one(x) == 0) || (x != 0 && rightmost_one(x) == (1 << __builtin_ctz(x))));
+
+    if (x == UINT_MAX) {
+      break;
+    }
+  }
+}
\ No newline at end of file