不多说,直接看代码:
#include <iostream> #include <ctime> using namespace std; void foo(int data) { data *= data; } void test_funny_optimize() { //case 0 => result time : 1206 ms { clock_t startTime = clock(); for (long long i = 0; i < 1000000000LL; i ++) { foo(i); } clock_t stopTime = clock(); cout << endl; cout << "offset is 1" << endl; cout << "cost time : " << (stopTime - startTime) << " ms" << endl; } //case 1 => result time : 545 ms { clock_t startTime = clock(); for (long long i = 0; i < 1000000000LL; i += 2) { foo(i); foo(i + 1); } clock_t stopTime = clock(); cout << endl; cout << "offset is 2" << endl; cout << "cost time : " << (stopTime - startTime) << " ms" << endl; } //case 2 => result time : 347 ms { clock_t startTime = clock(); for (long long i = 0; i < 1000000000LL; i += 3) { foo(i); foo(i + 1); foo(i + 2); } clock_t stopTime = clock(); cout << endl; cout << "offset is 3" << endl; cout << "cost time : " << (stopTime - startTime) << " ms" << endl; } //case 3 => result time : 102 ms { clock_t startTime = clock(); for (long long i = 0; i < 1000000000LL; i += 10) { foo(i); foo(i + 1); foo(i + 2); foo(i + 3); foo(i + 4); foo(i + 5); foo(i + 6); foo(i + 7); foo(i + 8); foo(i + 9); } clock_t stopTime = clock(); cout << endl; cout << "offset is 10" << endl; cout << "cost time : " << (stopTime - startTime) << " ms" << endl; } }
int main(int argc, char* argv[])
{
test_funny_optimize();
return 0;
}
vs2013 release模式编译,代码之后是执行结果:
当然,这个方法是在循环次数很大时作用才大。