Add memcpy example benchmarks

Author: nvzqz

examples/Cargo.toml

@@ -73,6 +73,10 @@ required-features = ["image"]
 name = "math"
 harness = false
 
+[[bench]]
+name = "memcpy"
+harness = false
+
 [[bench]]
 name = "panic"
 harness = false

examples/benches/memcpy.rs

@@ -0,0 +1,74 @@
+use divan::{counter::BytesCount, Bencher};
+use fastrand::Rng;
+
+fn main() {
+    divan::main();
+}
+
+const LENS: &[usize] = &[
+    1,
+    2,
+    8,
+    16,
+    64,
+    512,
+    1024 * 4,
+    1024 * 16,
+    1024 * 64,
+    1024 * 256,
+    1024 * 1024,
+    1024 * 1024 * 4,
+];
+
+fn gen_inputs(len: usize) -> impl FnMut() -> [Box<[u8]>; 2] {
+    let mut rng = Rng::default();
+    move || {
+        // Very buffers by length rather than adhere to nice numbers.
+        let max_len = len + (len / 8);
+        let lens = [rng.usize(len..=max_len), rng.usize(len..=max_len)];
+
+        lens.map(|len| (0..len).map(|_| rng.u8(..)).collect())
+    }
+}
+
+#[divan::bench(consts = LENS)]
+fn memcpy<const N: usize>(bencher: Bencher) {
+    bencher.counter(BytesCount::new(N)).with_inputs(gen_inputs(N)).bench_local_refs(
+        |[src, dst]| unsafe {
+            let src = src.as_ptr().cast();
+            let dst = dst.as_mut_ptr().cast();
+            libc::memcpy(dst, src, N);
+        },
+    )
+}
+
+#[divan::bench(consts = LENS)]
+#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+fn movsb<const N: usize>(bencher: Bencher) {
+    use std::arch::asm;
+
+    bencher.counter(BytesCount::new(N)).with_inputs(gen_inputs(N)).bench_local_refs(
+        |[src, dst]| unsafe {
+            let src = src.as_ptr();
+            let dst = dst.as_mut_ptr();
+
+            #[cfg(target_arch = "x86")]
+            asm!(
+                "rep movsb",
+                inout("ecx") N => _,
+                inout("esi") src => _,
+                inout("edi") dst => _,
+                options(nostack, preserves_flags),
+            );
+
+            #[cfg(target_arch = "x86_64")]
+            asm!(
+                "rep movsb",
+                inout("rcx") N => _,
+                inout("rsi") src => _,
+                inout("rdi") dst => _,
+                options(nostack, preserves_flags),
+            );
+        },
+    )
+}