adding benchmark

Author: markisus

README.md

@@ -89,6 +89,44 @@ int main(int argc, char *argv[])
 }
 ```
 
+Benchmark
+-------
+We can observe speed ups for structure of arrays vs array of structs with the toy program benchmark.cc
+Here are the results using Visual Studio 2022 on Release mode on my laptop.
+
+```
+benchmark results ==============
+soa sort time 0.126592
+vec sort time 0.312302
+soa timestamp avg time 0.0018725
+vec timestamp avg time 0.0052643
+```
+
+The benchmark contains a small program concerning simulated sensor measurements. With a straightforward array of structs, we store metadata together with the actual sensor data together and then just push_back() these onto an std::vector.
+```c++
+struct SensorData {
+    std::array<double, 18> xyz;
+
+struct Measurement {
+    Id sensor_id;
+    Id object_id;
+    double timestamp;
+    SensorData data;
+};
+
+...
+
+std::vector<Measurement> measurements_vec;
+measurements_vec.push_back(m);
+```
+Alternatively, we could split the metadata and sensor data apart into a structure of arrays.
+```c++
+vapid::soa<Id, Id, double, SensorData> measurements_soa;
+soa.insert(m.sensor_id, m.object_id, m.timestamp, m.data);
+```
+
+The benchmark times the cost of sorting by sensor_id, and then the cost of finding the average measurement timestamp using an std::vector vs a vapid::soa.
+
 Manual Installation
 -----------
 Copy the vapid folder into your project and #include "vapid/soa.h"  

benchmark.cc

@@ -71,9 +71,9 @@ int main(int argc, char* argv[])
 {
     TicToc tictoc;
     double soa_sort_time = 0;
-    double soa_sum_time = 0;
+    double soa_ts_avg_time = 0;
     double vec_sort_time = 0;
-    double vec_sum_time = 0;
+    double vec_ts_avg_time = 0;
     TestCase t0 = TestCase::random();
     t0.measurements_soa.prepare_tmp();
 
@@ -89,11 +89,12 @@ int main(int argc, char* argv[])
 
         // soa sum
         tictoc.tic();
-        double soa_sum = 0;
+        double soa_ts_avg = 0;
         for (double d : t.measurements_soa.get_column<2>()) {
-            soa_sum += d;
+            soa_ts_avg += d;
         }
-        soa_sum_time += tictoc.toc();
+        soa_ts_avg /= t.measurements_soa.size();
+        soa_ts_avg_time += tictoc.toc();
 
         // vec sort
         tictoc.tic();
@@ -106,18 +107,19 @@ int main(int argc, char* argv[])
 
         // vec sum
         tictoc.tic();
-        double vec_sum = 0;
+        double vec_ts_avg = 0;
         for (const auto& meas : t.measurements_vec) {
-            vec_sum += meas.timestamp;
+            vec_ts_avg += meas.timestamp;
         }
-        vec_sum_time += tictoc.toc();
+        vec_ts_avg /= t.measurements_vec.size();
+        vec_ts_avg_time += tictoc.toc();
 
         if (argc == 1234) {
             // prevent optimization
             std::cout << t.measurements_soa.get_column<0>()[0] << "\n";
             std::cout << t.measurements_vec[0].timestamp << "\n";
-            std::cout << vec_sum << "\n";
-            std::cout << soa_sum << "\n";
+            std::cout << vec_ts_avg << "\n";
+            std::cout << soa_ts_avg << "\n";
 
         }
     }
@@ -126,8 +128,8 @@ int main(int argc, char* argv[])
     std::cout << "soa sort time " << soa_sort_time << std::endl;
     std::cout << "vec sort time " << vec_sort_time << std::endl;
 
-    std::cout << "soa sum time " << soa_sum_time << std::endl;
-    std::cout << "vec sum time " << vec_sum_time << std::endl;
+    std::cout << "soa timestamp avg time " << soa_ts_avg_time << std::endl;
+    std::cout << "vec timestamp avg time " << vec_ts_avg_time << std::endl;
 
     return 0;
 }