Print mean/stddev of the # of iterations.

src/benchmark.cc

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include <algorithm>
+
 #include "benchmark/benchmark.h"
 #include "benchmark/macros.h"
 #include "colorprint.h"
@@ -258,11 +260,15 @@ void ComputeStats(const std::vector<BenchmarkReporter::Run>& reports,
         Stat1MinMax_d(it->max_heapbytes_used, it->iterations);
   }
 
-  // Get the data from the accumulator to BenchmarkRunData's.
+  // Get the data from the accumulator to BenchmarkRunData's.  In the
+  // computations below we must multiply by the number of iterations since
+  // PrintRunData will divide by it.
   mean_data->benchmark_name = reports[0].benchmark_name + "_mean";
-  mean_data->iterations = real_accumulated_time_stat.numSamples();
-  mean_data->real_accumulated_time = real_accumulated_time_stat.sum();
-  mean_data->cpu_accumulated_time = cpu_accumulated_time_stat.sum();
+  mean_data->iterations = iterations_stat.Mean();
+  mean_data->real_accumulated_time = real_accumulated_time_stat.Mean() *
+                                     mean_data->iterations;
+  mean_data->cpu_accumulated_time = cpu_accumulated_time_stat.Mean() *
+                                    mean_data->iterations;
   mean_data->bytes_per_second = bytes_per_second_stat.Mean();
   mean_data->items_per_second = items_per_second_stat.Mean();
   mean_data->max_heapbytes_used = max_heapbytes_used_stat.max();
@@ -278,9 +284,17 @@ void ComputeStats(const std::vector<BenchmarkReporter::Run>& reports,
 
   stddev_data->benchmark_name = reports[0].benchmark_name + "_stddev";
   stddev_data->report_label = mean_data->report_label;
-  stddev_data->iterations = real_accumulated_time_stat.numSamples();
-  // We multiply by the number of iterations since PrintRunData expects a total
-  // time.
+  stddev_data->iterations = iterations_stat.StdDev();
+  // Ugly hack here!  iterations_stat.StdDev() above may be 0 if all the
+  // repetitions have the same number of iterations.  Blindly multiplying by 0
+  // in the computation of real/cpu_accumulated_time below would lead to 0/0 in
+  // PrintRunData.  To avoid this, we set the number of iterations to something
+  // negative here, and PrintRunData prints it as 0 (see the std::max there).
+  // Thus the stddev of both the number of iterations and the times are printed
+  // correctly.
+  if (stddev_data->iterations == 0) {
+    stddev_data->iterations = -1;
+  }
   stddev_data->real_accumulated_time = real_accumulated_time_stat.StdDev() *
                                        stddev_data->iterations;
   stddev_data->cpu_accumulated_time = cpu_accumulated_time_stat.StdDev() *
@@ -473,7 +487,8 @@ void ConsoleReporter::PrintRunData(const BenchmarkReporter::Run& result) const {
                   (static_cast<double>(result.iterations)),
               (result.cpu_accumulated_time * 1e9) /
                   (static_cast<double>(result.iterations)));
-  ColorPrintf(COLOR_CYAN, "%10lld", result.iterations);
+  // See ComputeStats for why a negative value is printed as 0.
+  ColorPrintf(COLOR_CYAN, "%10lld", std::max(0LL, result.iterations));
   ColorPrintf(COLOR_DEFAULT, "%*s %*s %s %s\n",
               13, rate.c_str(),
               18, items.c_str(),