add write_bytes() test for a larger-than-u128 struct

Author: David Renshaw

tests/run-pass/write-bytes.rs

@@ -1,3 +1,11 @@
+#[repr(C)]
+#[derive(Copy, Clone)]
+struct Foo {
+    a: u64,
+    b: u64,
+    c: u64,
+}
+
 fn main() {
     const LENGTH: usize = 10;
     let mut v: [u64; LENGTH] = [0; LENGTH];
@@ -14,4 +22,24 @@ fn main() {
     for idx in 0..LENGTH {
         assert_eq!(v[idx], 0xabababababababab);
     }
+
+    // -----
+
+    let mut w: [Foo; LENGTH] = [Foo { a: 0, b: 0, c: 0 }; LENGTH];
+    for idx in 0..LENGTH {
+        assert_eq!(w[idx].a, 0);
+        assert_eq!(w[idx].b, 0);
+        assert_eq!(w[idx].c, 0);
+    }
+
+    unsafe {
+        let p = w.as_mut_ptr();
+        ::std::ptr::write_bytes(p, 0xcd, LENGTH);
+    }
+
+    for idx in 0..LENGTH {
+        assert_eq!(w[idx].a, 0xcdcdcdcdcdcdcdcd);
+        assert_eq!(w[idx].b, 0xcdcdcdcdcdcdcdcd);
+        assert_eq!(w[idx].c, 0xcdcdcdcdcdcdcdcd);
+    }
 }