Extract util::Xor, Add key_offset option, Add bench

src/bench/bench.h

@@ -14,7 +14,7 @@
 #include <string>
 #include <vector>
 
-#include <bench/nanobench.h>
+#include <bench/nanobench.h> // IWYU pragma: export
 
 /*
  * Usage:

src/bench/xor.cpp

@@ -0,0 +1,24 @@
+// Copyright (c) The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or https://opensource.org/license/mit/.
+
+#include <bench/bench.h>
+
+#include <random.h>
+#include <streams.h>
+
+#include <cstddef>
+#include <vector>
+
+static void Xor(benchmark::Bench& bench)
+{
+    FastRandomContext frc{/*fDeterministic=*/true};
+    auto data{frc.randbytes<std::byte>(1024)};
+    auto key{frc.randbytes<std::byte>(31)};
+
+    bench.batch(data.size()).unit("byte").run([&] {
+        util::Xor(data, key);
+    });
+}
+
+BENCHMARK(Xor, benchmark::PriorityLevel::HIGH);