/*
 * Random_Call1.cpp
 *
 *  Created on: 2013/09/23
 *      Author: まっちゃん
 */
 
// 826 名前：デフォルトの名無しさん[sage] 投稿日：2013/09/23(月) 20:13:03.86
// 結局メモリからコール先をロードする際にはレジスタでコールテーブルからオフセット値を
// 読み込んで初めてコール先が決定するので、コール先がアトランダムに変わる場合
// 全くと言って良いほど分岐予測が当たらない
 
// これはCの関数ポインタ配列でも同じだと思う
// 誰かベンチマーク取ってみてよ
// 同じ関数ばかり関数ポインタで呼ぶのと、乱数で呼び先をランダムに変えた場合
 
#include <iostream>
#include <chrono>
#include <cstdlib>
#include <ctime>
 
class Duration {
  std::chrono::high_resolution_clock::time_point beg, duration;
public:
  Duration() {
    beg = std::chrono::high_resolution_clock::now();
  }
  ~Duration() {
    duration = std::chrono::high_resolution_clock::now();
    std::cout << std::chrono::duration_cast<std::chrono::milliseconds>(duration - beg).count() << "ms" << std::endl;
  }
};
 
const int N = 10000000;
 
int rnd[N];
 
void func1()
{
  return;
}
 
void func2()
{
  return;
}
 
void func3()
{
  return;
}
 
void func4()
{
  return;
}
 
int main()
{
  void (*func[])() = { func1, func2, func3, func4 }; // Avoid std::function costs
 
  {
    std::cout << "The same function call" << std::endl;
    Duration d;
 
    for (int i = 0; i < N; i++)
      func[0]();
  }
 
  {
    std::srand(std::time(0));
    for (int i = 0; i < N; i++)
      rnd[i] = std::rand() % 4; // Avoid std::rand() costs
    std::cout << "Random function call" << std::endl;
    Duration d;
 
    for (int i = 0; i < N; i++)
      func[rnd[i]]();
  }
}
 
 

LyoKICogUmFuZG9tX0NhbGwxLmNwcAogKgogKiAgQ3JlYXRlZCBvbjogMjAxMy8wOS8yMwogKiAgICAgIEF1dGhvcjog44G+44Gj44Gh44KD44KTCiAqLwoKLy8gODI2IOWQjeWJje+8muODh+ODleOCqeODq+ODiOOBruWQjeeEoeOBl+OBleOCk1tzYWdlXSDmipXnqL/ml6XvvJoyMDEzLzA5LzIzKOaciCkgMjA6MTM6MDMuODYKLy8g57WQ5bGA44Oh44Oi44Oq44GL44KJ44Kz44O844Or5YWI44KS44Ot44O844OJ44GZ44KL6Zqb44Gr44Gv44Os44K444K544K/44Gn44Kz44O844Or44OG44O844OW44Or44GL44KJ44Kq44OV44K744OD44OI5YCk44KSCi8vIOiqreOBv+i+vOOCk+OBp+WIneOCgeOBpuOCs+ODvOODq+WFiOOBjOaxuuWumuOBmeOCi+OBruOBp+OAgeOCs+ODvOODq+WFiOOBjOOCouODiOODqeODs+ODgOODoOOBq+WkieOCj+OCi+WgtOWQiAovLyDlhajjgY/jgajoqIDjgaPjgaboia/jgYTjgbvjganliIblspDkuojmuKzjgYzlvZPjgZ/jgonjgarjgYQKCi8vIOOBk+OCjOOBr0Pjga7plqLmlbDjg53jgqTjg7Pjgr/phY3liJfjgafjgoLlkIzjgZjjgaDjgajmgJ3jgYYKLy8g6Kqw44GL44OZ44Oz44OB44Oe44O844Kv5Y+W44Gj44Gm44G/44Gm44KICi8vIOWQjOOBmOmWouaVsOOBsOOBi+OCiumWouaVsOODneOCpOODs+OCv+OBp+WRvOOBtuOBruOBqOOAgeS5seaVsOOBp+WRvOOBs+WFiOOCkuODqeODs+ODgOODoOOBq+WkieOBiOOBn+WgtOWQiAoKI2luY2x1ZGUgPGlvc3RyZWFtPgojaW5jbHVkZSA8Y2hyb25vPgojaW5jbHVkZSA8Y3N0ZGxpYj4KI2luY2x1ZGUgPGN0aW1lPgoKY2xhc3MgRHVyYXRpb24gewogIHN0ZDo6Y2hyb25vOjpoaWdoX3Jlc29sdXRpb25fY2xvY2s6OnRpbWVfcG9pbnQgYmVnLCBkdXJhdGlvbjsKcHVibGljOgogIER1cmF0aW9uKCkgewogICAgYmVnID0gc3RkOjpjaHJvbm86OmhpZ2hfcmVzb2x1dGlvbl9jbG9jazo6bm93KCk7CiAgfQogIH5EdXJhdGlvbigpIHsKICAgIGR1cmF0aW9uID0gc3RkOjpjaHJvbm86OmhpZ2hfcmVzb2x1dGlvbl9jbG9jazo6bm93KCk7CiAgICBzdGQ6OmNvdXQgPDwgc3RkOjpjaHJvbm86OmR1cmF0aW9uX2Nhc3Q8c3RkOjpjaHJvbm86Om1pbGxpc2Vjb25kcz4oZHVyYXRpb24gLSBiZWcpLmNvdW50KCkgPDwgIm1zIiA8PCBzdGQ6OmVuZGw7CiAgfQp9OwoKY29uc3QgaW50IE4gPSAxMDAwMDAwMDsKCmludCBybmRbTl07Cgp2b2lkIGZ1bmMxKCkKewogIHJldHVybjsKfQoKdm9pZCBmdW5jMigpCnsKICByZXR1cm47Cn0KCnZvaWQgZnVuYzMoKQp7CiAgcmV0dXJuOwp9Cgp2b2lkIGZ1bmM0KCkKewogIHJldHVybjsKfQoKaW50IG1haW4oKQp7CiAgdm9pZCAoKmZ1bmNbXSkoKSA9IHsgZnVuYzEsIGZ1bmMyLCBmdW5jMywgZnVuYzQgfTsgLy8gQXZvaWQgc3RkOjpmdW5jdGlvbiBjb3N0cwoKICB7CiAgICBzdGQ6OmNvdXQgPDwgIlRoZSBzYW1lIGZ1bmN0aW9uIGNhbGwiIDw8IHN0ZDo6ZW5kbDsKICAgIER1cmF0aW9uIGQ7CgogICAgZm9yIChpbnQgaSA9IDA7IGkgPCBOOyBpKyspCiAgICAgIGZ1bmNbMF0oKTsKICB9CgogIHsKICAgIHN0ZDo6c3JhbmQoc3RkOjp0aW1lKDApKTsKICAgIGZvciAoaW50IGkgPSAwOyBpIDwgTjsgaSsrKQogICAgICBybmRbaV0gPSBzdGQ6OnJhbmQoKSAlIDQ7IC8vIEF2b2lkIHN0ZDo6cmFuZCgpIGNvc3RzCiAgICBzdGQ6OmNvdXQgPDwgIlJhbmRvbSBmdW5jdGlvbiBjYWxsIiA8PCBzdGQ6OmVuZGw7CiAgICBEdXJhdGlvbiBkOwoKICAgIGZvciAoaW50IGkgPSAwOyBpIDwgTjsgaSsrKQogICAgICBmdW5jW3JuZFtpXV0oKTsKICB9Cn0KCg==