bench: switch to std::chrono for time measurements

std::chrono removes portability issues.

Rather than storing doubles, store the untouched time_points. Then
convert to nanoseconds for display. This allows for maximum precision, while
keeping results comparable between differing hardware/operating systems.

Also, display full nanosecond counts rather than sub-second floats.

1 files changed, 12 insertions, 7 deletions

diff --git a/src/bench/bench.h b/src/bench/bench.h
index 79109eaa56..d7037e1f33 100644
--- a/src/bench/bench.h
+++ b/src/bench/bench.h
@@ -9,6 +9,7 @@
 #include <limits>
 #include <map>
 #include <string>
+#include <chrono>
 
 #include <boost/preprocessor/cat.hpp>
 #include <boost/preprocessor/stringize.hpp>
@@ -37,11 +38,15 @@ BENCHMARK(CODE_TO_TIME);
  
 namespace benchmark {
 
+    using clock = std::chrono::high_resolution_clock;
+    using time_point = clock::time_point;
+    using duration = clock::duration;
+
     class State {
         std::string name;
-        double maxElapsed;
-        double beginTime;
-        double lastTime, minTime, maxTime;
+        duration maxElapsed;
+        time_point beginTime, lastTime;
+        duration minTime, maxTime;
         uint64_t count;
         uint64_t countMask;
         uint64_t beginCycles;
@@ -49,9 +54,9 @@ namespace benchmark {
         uint64_t minCycles;
         uint64_t maxCycles;
     public:
-        State(std::string _name, double _maxElapsed) : name(_name), maxElapsed(_maxElapsed), count(0) {
-            minTime = std::numeric_limits<double>::max();
-            maxTime = std::numeric_limits<double>::min();
+        State(std::string _name, duration _maxElapsed) : name(_name), maxElapsed(_maxElapsed), count(0) {
+            minTime = duration::max();
+            maxTime = duration::zero();
             minCycles = std::numeric_limits<uint64_t>::max();
             maxCycles = std::numeric_limits<uint64_t>::min();
             countMask = 1;
@@ -69,7 +74,7 @@ namespace benchmark {
     public:
         BenchRunner(std::string name, BenchFunction func);
 
-        static void RunAll(double elapsedTimeForOne=1.0);
+        static void RunAll(duration elapsedTimeForOne = std::chrono::seconds(1));
     };
 }