Fix ChaCha20 Alignment Issues

benchmarks/stdlib/crypto/chacha20.c3

@@ -2,6 +2,7 @@
 // Use of this source code is governed by the MIT license
 // a copy of which can be found in the LICENSE_STDLIB file.
 module chacha20_benchmarks;
+
 import std::crypto::chacha20;
 
 
@@ -15,11 +16,24 @@ const char[] KEY = x'98bef1469be7269837a45bfbc92a5a6ac762507cf96443bf33b96b1bd4c
 const char[] NONCE = x'44e792d63335abb1582e9253';
 const uint COUNTER = 42;
 
-char[] one_megabyte = { [0..1024*1024] = 0xA5 };
+char[] one_mb @align(ulong.sizeof) = { [0..1024*1024] = 0xA5 };
 
 // This doesn't test both encryption + decryption, because it's a symmetric operation that shares
 //   a single common data transformation. Testing one limb is enough.
 fn void gogo_chacha20() @benchmark
 {
-	chacha20::encrypt_mut(one_megabyte[..], KEY, NONCE, COUNTER);
+	chacha20::encrypt_mut(one_mb[..], KEY, NONCE, COUNTER);
+}
+
+// Check what the speed of an unligned buffer looks like.
+fn void gogo_chacha20_unaligned() @benchmark => @pool()
+{
+    char[] copy = mem::talloc_array(char, one_mb.len + 3);
+    char[] im_off_slightly = copy[3..];
+    copy[3..] = one_mb[..];
+    assert((usz)im_off_slightly.ptr % usz.sizeof > 0);
+
+    runtime::@start_benchmark();
+	chacha20::encrypt_mut(im_off_slightly, KEY, NONCE, COUNTER);
+    runtime::@end_benchmark();
 }