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+// Copyright 2019 Google LLC
+// SPDX-License-Identifier: Apache-2.0
+//
+// 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 "hwy/nanobenchmark.h"
+
+#include <inttypes.h>
+#include <stdint.h>
+#include <stdio.h>
+
+#include <random>
+
+#include "hwy/tests/test_util-inl.h"
+
+namespace hwy {
+namespace {
+
+// Governs duration of test; avoid timeout in debug builds.
+#if HWY_IS_DEBUG_BUILD
+constexpr size_t kMaxEvals = 3;
+#else
+constexpr size_t kMaxEvals = 4;
+#endif
+
+FuncOutput Div(const void*, FuncInput in) {
+ // Here we're measuring the throughput because benchmark invocations are
+ // independent. Any dividend will do; the divisor is nonzero.
+ return 0xFFFFF / in;
+}
+
+template <size_t N>
+void MeasureDiv(const FuncInput (&inputs)[N]) {
+ printf("Measuring integer division (output on final two lines)\n");
+ Result results[N];
+ Params params;
+ params.max_evals = kMaxEvals;
+ const size_t num_results = Measure(&Div, nullptr, inputs, N, results, params);
+ for (size_t i = 0; i < num_results; ++i) {
+ printf("%5" PRIu64 ": %6.2f ticks; MAD=%4.2f%%\n",
+ static_cast<uint64_t>(results[i].input), results[i].ticks,
+ results[i].variability * 100.0);
+ }
+}
+
+std::mt19937 rng;
+
+// A function whose runtime depends on rng.
+FuncOutput Random(const void* /*arg*/, FuncInput in) {
+ const size_t r = rng() & 0xF;
+ uint32_t ret = in;
+ for (size_t i = 0; i < r; ++i) {
+ ret /= ((rng() & 1) + 2);
+ }
+ return ret;
+}
+
+// Ensure the measured variability is high.
+template <size_t N>
+void MeasureRandom(const FuncInput (&inputs)[N]) {
+ Result results[N];
+ Params p;
+ p.max_evals = kMaxEvals;
+ p.verbose = false;
+ const size_t num_results = Measure(&Random, nullptr, inputs, N, results, p);
+ for (size_t i = 0; i < num_results; ++i) {
+ NANOBENCHMARK_CHECK(results[i].variability > 1E-3);
+ }
+}
+
+TEST(NanobenchmarkTest, RunAll) {
+ const int unpredictable = Unpredictable1(); // == 1, unknown to compiler.
+ static const FuncInput inputs[] = {static_cast<FuncInput>(unpredictable) + 2,
+ static_cast<FuncInput>(unpredictable + 9)};
+
+ MeasureDiv(inputs);
+ MeasureRandom(inputs);
+}
+
+} // namespace
+} // namespace hwy