add benchmark comparing unsafe version

Cargo.toml

@@ -10,3 +10,10 @@ edition = "2021"
 
 [dev-dependencies]
 quickcheck = "0.6"
+criterion = "0.4.0"
+rand = "0.8.5"
+
+[[bench]]
+name = "benches"
+harness = false
+path="benches/benches.rs"

benches/benches.rs

@@ -0,0 +1,58 @@
+extern crate arrayref;
+
+use arrayref::array_ref;
+use criterion::{criterion_group, criterion_main, Criterion, black_box};
+use rand::{Rng, SeedableRng};
+
+pub fn array_refs_random_data(c: &mut Criterion) {
+    let x = [0,1,2,3,4,5,6,7,8,9];
+    c.bench_function("Simple bench", |b| {
+        b.iter(|| {
+            let a = black_box(array_ref!(x, 0, 5));
+            let a = black_box(array_ref!(x, 5, 5));
+        })
+    });
+
+    c.bench_function("Simple bench unsafe", |b| {
+        b.iter(|| {
+            let a = black_box(array_ref_unsafe!(x, 0, 5));
+            let a = black_box(array_ref_unsafe!(x, 5, 5));
+        })
+    });
+
+    let x = [0u8; (1usize << 20) - 1];
+    c.bench_function("large array bench", |b| {
+        b.iter(|| {
+            let a = black_box(array_ref!(x, 0, 10001));
+            let a = black_box(array_ref!(x, 10001, 999999));
+        })
+    });
+
+    c.bench_function("large array bench unsafe", |b| {
+        b.iter(|| {
+            let a = black_box(array_ref_unsafe!(x, 0, 10001));
+            let a = black_box(array_ref_unsafe!(x, 10001, 999999));
+        })
+    });
+}
+
+criterion_group!(benches, array_refs_random_data);
+criterion_main!(benches);
+
+#[macro_export]
+macro_rules! array_ref_unsafe {
+    ($arr:expr, $offset:expr, $len:expr) => {{
+        {
+            #[inline]
+            unsafe fn as_array<T>(slice: &[T]) -> &[T; $len] {
+                &*(slice.as_ptr() as *const [_; $len])
+            }
+            let offset = $offset;
+            let slice = & $arr[offset..offset + $len];
+            #[allow(unused_unsafe)]
+            unsafe {
+                as_array(slice)
+            }
+        }
+    }}
+}