Add C++ decimal benchmark

cpp/src/arrow/util/CMakeLists.txt

@@ -60,5 +60,6 @@ ADD_ARROW_TEST(rle-encoding-test)
 ADD_ARROW_TEST(stl-util-test)
 
 ADD_ARROW_BENCHMARK(bit-util-benchmark)
+ADD_ARROW_BENCHMARK(decimal-benchmark)
 
 add_subdirectory(variant)

cpp/src/arrow/util/decimal-benchmark.cc

@@ -0,0 +1,44 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you 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 "benchmark/benchmark.h"
+
+#include <string>
+#include <vector>
+
+#include "arrow/util/decimal.h"
+
+namespace arrow {
+namespace Decimal {
+
+static void BM_FromString(benchmark::State& state) {  // NOLINT non-const reference
+  std::vector<std::string> values = {"0", "1.23", "12.345e6", "-12.345e-6"};
+
+  while (state.KeepRunning()) {
+    for (const auto& value : values) {
+      Decimal128 dec;
+      int32_t scale, precision;
+      Decimal128::FromString(value, &dec, &scale, &precision);
+    }
+  }
+  state.SetItemsProcessed(state.iterations() * values.size());
+}
+
+BENCHMARK(BM_FromString)->Repetitions(3)->Unit(benchmark::kMicrosecond);
+
+}  // namespace Decimal
+}  // namespace arrow