include Google Benchmark submodule, and add a benchmark

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "cmake-modules"]
 	path = cmake-modules
 	url = https://github.com/bilke/cmake-modules.git
+[submodule "bench/benchmark"]
+	path = bench/benchmark
+	url = https://github.com/google/benchmark.git

CMakeLists.txt

@@ -44,3 +44,10 @@ set_target_properties(Boost.Real_headers PROPERTIES
                                                  EXCLUDE_FROM_ALL TRUE
                                                  EXCLUDE_FROM_DEFAULT_BUILD TRUE
                                                  LINKER_LANGUAGE CXX)
+
+#Google Benchmark, turn on/off with -DBENCH=ON or OFF
+find_package(Threads REQUIRED)
+option(BENCH "Build benchmarks" ON)
+if(BENCH)
+    add_subdirectory(bench)
+endif()

bench/CMakeLists.txt

@@ -0,0 +1,18 @@
+set(BENCHMARK_ENABLE_TESTING OFF CACHE BOOL "Suppressing benchmark's tests" FORCE)
+
+add_subdirectory(benchmark)
+include_directories(benchmark/include
+    include)
+
+set(bench_list
+    addition_bench.cpp
+    )
+
+add_executable(main_bench ${bench_list})
+
+
+target_link_libraries(main_bench
+    benchmark
+    Boost.Real
+    ${CMAKE_THREAD_LIBS_INIT}
+    )

bench/addition_bench.cpp

@@ -0,0 +1,19 @@
+#include <bench_helpers.hpp>
+#include <benchmark/benchmark.h>
+#include <real/real.hpp>
+#include <iostream>
+
+// this process uses an absurd amount of memory
+// sums 10,000 reals, then evaluates.
+static void BM_RealAddition10000(benchmark::State& state) {
+    boost::real::real a ("1.2");
+    boost::real::real c ("0");
+
+    for (auto i : state)
+        for (int i = 0; i < 10000; i++)
+            c += a;
+    std::cout << c << '\n';
+}
+BENCHMARK(BM_RealAddition10000);
+
+BENCHMARK_MAIN();

bench/include/bench_helpers.hpp

@@ -0,0 +1,10 @@
+#ifndef BOOST_REAL_BENCH_HELPERS_HPP
+#define BOOST_REAL_BENCH_HELPERS_HPP
+
+
+#include <real/real.hpp>
+
+unsigned int boost::real::real::maximum_precision = 10;
+unsigned int boost::real::real_algorithm::maximum_precision = 10;
+
+#endif //BOOST_REAL_BENCH_HELPERS_HPP