Update c++ to print throughput in MB/s instead of ms

Author: dtolnay

cpp/main.cc

@@ -29,23 +29,24 @@ void bench(const char* path) {
   in.read(&s[0], s.size());
   in.close();
   auto c_str = s.c_str();
+  auto bytes = s.size();
 
   Timer timer;
 
   {
-    auto min = std::numeric_limits<float>::infinity();
+    std::chrono::microseconds min{std::numeric_limits<std::chrono::microseconds::rep>::max()};
     for (int i = 0; i < 256; i++) {
       rapidjson::Document d;
       timer.reset();
       d.Parse(c_str);
       assert(!d.HasParseError());
-      min = std::min(min, timer.millis());
+      min = std::min(min, timer.micros());
     }
-    std::cout << path << " parse dom: " << min << "ms" << std::endl;
+    std::cout << path << " parse dom: " << throughput(min, bytes) << " MB/s" << std::endl;
   }
 
   {
-    auto min = std::numeric_limits<float>::infinity();
+    std::chrono::microseconds min{std::numeric_limits<std::chrono::microseconds::rep>::max()};
     rapidjson::Document d;
     d.Parse(c_str);
     assert(!d.HasParseError());
@@ -56,13 +57,13 @@ void bench(const char* path) {
       timer.reset();
       auto result = d.Accept(writer);
       assert(result);
-      min = std::min(min, timer.millis());
+      min = std::min(min, timer.micros());
     }
-    std::cout << path << " stringify dom: " << min << "ms" << std::endl;
+    std::cout << path << " stringify dom: " << throughput(min, bytes) << " MB/s" << std::endl;
   }
 
   {
-    auto min = std::numeric_limits<float>::infinity();
+    std::chrono::microseconds min{std::numeric_limits<std::chrono::microseconds::rep>::max()};
     for (int i = 0; i < 256; i++) {
       rapidjson::Reader reader;
       Handler handler;
@@ -79,13 +80,13 @@ void bench(const char* path) {
 #endif
       assert(result);
       auto keep = handler.Get();
-      min = std::min(min, timer.millis());
+      min = std::min(min, timer.micros());
     }
-    std::cout << path << " parse struct: " << min << "ms" << std::endl;
+    std::cout << path << " parse struct: " << throughput(min, bytes) << " MB/s" << std::endl;
   }
 
   {
-    auto min = std::numeric_limits<float>::infinity();
+    std::chrono::microseconds min{std::numeric_limits<std::chrono::microseconds::rep>::max()};
     rapidjson::Reader reader;
     Handler handler;
     rapidjson::StringStream ss(c_str);
@@ -99,9 +100,9 @@ void bench(const char* path) {
       rapidjson::Writer<rapidjson::StringBuffer> writer(sb);
       timer.reset();
       Serialize(d, writer);
-      min = std::min(min, timer.millis());
+      min = std::min(min, timer.micros());
     }
-    std::cout << path << " stringify struct: " << min << "ms" << std::endl;
+    std::cout << path << " stringify struct: " << throughput(min, bytes) << " MB/s" << std::endl;
   }
 }
 

cpp/timer.cc

@@ -6,6 +6,21 @@ void Timer::reset() {
   begin_ = clock_::now();
 }
 
-float Timer::millis() const {
-  return std::chrono::duration_cast<milli_>(clock_::now() - begin_).count();
+std::chrono::microseconds Timer::micros() const {
+  return std::chrono::duration_cast<std::chrono::microseconds>(clock_::now() - begin_);
+}
+
+// matches json-benchmark/src/lib.rs
+uint64_t throughput(std::chrono::microseconds dur, size_t bytes) {
+  auto mbps = bytes / static_cast<uint64_t>(dur.count());
+
+  // Round to two significant digits.
+  if (mbps > 100) {
+    if (mbps % 10 >= 5) {
+      mbps += 10;
+    }
+    mbps = mbps / 10 * 10;
+  }
+
+  return mbps;
 }

cpp/timer.h

@@ -7,12 +7,13 @@ class Timer {
  public:
   Timer();
   void reset();
-  float millis() const;
+  std::chrono::microseconds micros() const;
 
  private:
   typedef std::chrono::high_resolution_clock clock_;
-  typedef std::chrono::duration<float, std::milli> milli_;
   std::chrono::time_point<clock_> begin_;
 };
 
+uint64_t throughput(std::chrono::microseconds dur, size_t bytes);
+
 #endif // TIMER_H_