Create android-base/format.h that includes fmtlib headers

We're already including fmtlib statically in libbase, so let's also
expose its functionality directly.

Also create a small benchmark of the most common operations for
format() and StringPrintf(): int, float, and string arguments.  Note
that fmt::format is faster than StringPrintf() in all of these cases.

Test: build, run benchmark
Change-Id: I1e18f13673dd89ea936ea5c51418fad723495b08

base/Android.bp

@@ -182,3 +182,21 @@ cc_test {
     },
     test_suites: ["device-tests"],
 }
+
+cc_benchmark {
+    name: "libbase_benchmark",
+    defaults: ["libbase_cflags_defaults"],
+
+    srcs: ["format_benchmark.cpp"],
+    shared_libs: ["libbase"],
+
+    compile_multilib: "both",
+    multilib: {
+        lib32: {
+            suffix: "32",
+        },
+        lib64: {
+            suffix: "64",
+        },
+    },
+}

base/format_benchmark.cpp

@@ -0,0 +1,80 @@
+/*
+ * Copyright (C) 2019 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 "android-base/format.h"
+
+#include <limits>
+
+#include <benchmark/benchmark.h>
+
+#include "android-base/stringprintf.h"
+
+using android::base::StringPrintf;
+
+static void BenchmarkFormatInt(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(fmt::format("{} {} {}", 42, std::numeric_limits<int>::min(),
+                                         std::numeric_limits<int>::max()));
+  }
+}
+
+BENCHMARK(BenchmarkFormatInt);
+
+static void BenchmarkStringPrintfInt(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(StringPrintf("%d %d %d", 42, std::numeric_limits<int>::min(),
+                                          std::numeric_limits<int>::max()));
+  }
+}
+
+BENCHMARK(BenchmarkStringPrintfInt);
+
+static void BenchmarkFormatFloat(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(fmt::format("{} {} {}", 42.42, std::numeric_limits<float>::min(),
+                                         std::numeric_limits<float>::max()));
+  }
+}
+
+BENCHMARK(BenchmarkFormatFloat);
+
+static void BenchmarkStringPrintfFloat(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(StringPrintf("%f %f %f", 42.42, std::numeric_limits<float>::min(),
+                                          std::numeric_limits<float>::max()));
+  }
+}
+
+BENCHMARK(BenchmarkStringPrintfFloat);
+
+static void BenchmarkFormatStrings(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(fmt::format("{} hello there {}", "hi,", "!!"));
+  }
+}
+
+BENCHMARK(BenchmarkFormatStrings);
+
+static void BenchmarkStringPrintfStrings(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(StringPrintf("%s hello there %s", "hi,", "!!"));
+  }
+}
+
+BENCHMARK(BenchmarkStringPrintfStrings);
+
+// Run the benchmark
+BENCHMARK_MAIN();

base/include/android-base/format.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+
+#pragma once
+
+// We include fmtlib here as an alias, since libbase will have fmtlib statically linked already.
+// It is accessed through its normal fmt:: namespace.
+#include <fmt/core.h>
+#include <fmt/format.h>
+#include <fmt/ostream.h>
+#include <fmt/printf.h>
+#include <fmt/time.h>

base/include/android-base/result.h

@@ -79,9 +79,8 @@
 #include <sstream>
 #include <string>
 
-#include <fmt/ostream.h>
-
 #include "android-base/expected.h"
+#include "android-base/format.h"
 
 namespace android {
 namespace base {