Support memory alignment tests for string_benchmark.cpp

Test: Manually verify that benchmark times are similar and add a unit test.
Change-Id: Idaaeb4c8c3629f797ffd8d0c86c8d7b7b9653181
diff --git a/benchmarks/tests/benchmark_test.cpp b/benchmarks/tests/benchmark_test.cpp
new file mode 100644
index 0000000..df7b686
--- /dev/null
+++ b/benchmarks/tests/benchmark_test.cpp
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+#include <util.h>
+
+TEST(benchmark, memory_align) {
+  std::vector<char> buf(100);
+  for (size_t alignment = 1; alignment <= 32; alignment *= 2) {
+    for (size_t or_mask = 0; or_mask < alignment; ++or_mask) {
+      uintptr_t aligned_ptr = reinterpret_cast<uintptr_t>(GetAlignedMemory(buf.data(), alignment,
+                                                                           or_mask));
+      ASSERT_EQ(aligned_ptr % alignment, or_mask);
+      ASSERT_EQ(aligned_ptr & alignment, alignment);
+    }
+  }
+}
+
+TEST(benchmark, ptr_align) {
+  std::vector<char> buf;
+  for (size_t alignment = 1; alignment <= 2048; alignment *= 2) {
+    uintptr_t aligned_ptr = reinterpret_cast<uintptr_t>(GetAlignedPtr(&buf, alignment, 100));
+    ASSERT_EQ(aligned_ptr & alignment, alignment);
+    ASSERT_EQ(aligned_ptr & (alignment - 1), 0u);
+  }
+}