add cpu caching tester.

.drone.yml

@@ -21,4 +21,7 @@ steps:
 
       - cd misc || exit
       - g++ sizeof.cpp -o sizeof && ./sizeof
+      - g++ caching.cpp -o caching && ./caching
+      - echo "following program fails to show the effect of 'likely' due to CPU branch predictor."
+      - g++ likely.cpp -o likely && ./likely
       - cd -

misc/caching.cpp

@@ -0,0 +1,53 @@
+#include <iostream>
+#include <sys/time.h>
+#include <random>
+
+using namespace std;
+
+const int SIZE = 256 * 1024 * 1024;
+const int pagenum = 16 * 1024;
+const int pagesize = SIZE / pagenum;
+
+void xorsum_seq(int *data)
+{
+    int xorsum = 0;
+    timeval start, end;
+    gettimeofday(&start, nullptr);
+    for (int page = 0; page < pagenum; page++)
+    {
+        for (int idx = 0; idx < pagesize; idx++)
+            xorsum ^= data[page * pagesize + idx];
+    }
+
+    gettimeofday(&end, nullptr);
+    double usec = (end.tv_sec - start.tv_sec) + (double)(end.tv_usec - start.tv_usec) / 1000000;
+    cout << __func__ << " duration: " << usec << ", xorsum: " << xorsum << endl;
+}
+
+void xorsum_jmp(int *data)
+{
+    int xorsum = 0;
+    timeval start, end;
+    gettimeofday(&start, nullptr);
+    for (int idx = 0; idx < pagesize; idx++)
+    {
+        for (int page = 0; page < pagenum; page++)
+            xorsum ^= data[page * pagesize + idx];
+    }
+    gettimeofday(&end, nullptr);
+    double usec = (end.tv_sec - start.tv_sec) + (double)(end.tv_usec - start.tv_usec) / 1000000;
+    cout << __func__ << " duration: " << usec << ", xorsum: " << xorsum << endl;
+}
+
+int main()
+{
+    int *data = new int[SIZE];
+    int xorsum = 0;
+    srand(time(nullptr));
+    for (int idx = 0; idx < SIZE; idx++)
+    {
+        data[idx] = rand();
+    }
+    xorsum_seq(data);
+    xorsum_jmp(data);
+}