gistfile1.cpp

// On my system:
//   virtual call time: 4.340
//   non-virtual call time: 3.970
//   virtual call overhead 9.32%

#include <stdlib.h>
#include <time.h>
#include <stdio.h>

#define NOINLINE __attribute__ ((noinline))

#define N 1000000
#define M 100

class Compare {
 public:
  virtual int vcompare(const void *a, const void *b) {
    return *(int*)b - *(int*)a;
  }

  int compare(const void *a, const void *b) NOINLINE {
    return *(int*)b - *(int*)a;
  }
};

Compare* c;
int vcmp(const void *a, const void *b) { return c->vcompare(a, b); }
int icmp(const void *a, const void *b) { return c->compare(a, b); }

int main() {
  int *array = new int[N];
  c = new Compare();

  double vsec, isec;

  clock_t before = clock();
  for (int i = 0; i < M; i++) { qsort(array, N, sizeof(int), vcmp); }
  vsec = (double)(clock() - before) / CLOCKS_PER_SEC;
  printf("virtual call time: %0.3f\n", vsec);

  before = clock();
  for (int i = 0; i < M; i++) { qsort(array, N, sizeof(int), icmp); }
  isec = (double)(clock() - before) / CLOCKS_PER_SEC;
  printf("non-virtual call time: %0.3f\n", isec);
  printf("virtual call overhead %0.2f%%\n", (vsec - isec) * 100 / isec);
  return 0;
}