Question

i am interested how to put it in loop so that get real time which is taken by cpu to execute each different operation

#include<iostream>
#include<cstdlib>
#include<time.h>

using namespace std;
typedef unsigned __int64 uint64;
const uint64 m1=0x5555555555555555;
const uint64 m2=0x3333333333333333;
const uint64 m4=0x0f0f0f0f0f0f0f0f;
const uint64 m8=0x00ff00ff00ff00ff;
const uint64 m16=0x0000ffff0000ffff;
const uint64 m32=0x00000000ffffffff;
const uint64 hff=0xffffffffffffffff;
const uint64 h01=0x0101010101010101;

uint64 popcount_1(uint64 x)
{
    x=(x&m1)+((x>>1)&m1);
    x=(x&m2)+((x>>2)&m2);
    x=(x&m4)+((x>>4)&m4);
    x=(x&m8)+((x>>8)&m8);
    x=(x&m16)+((x>>16)&m16);
    x=(x&m32)+((x>>32)&m32);
    return (uint64)x;
}

//This uses fewer arithmetic operations than any other known
//implementation on machines with slow multiplication.
//It uses 17 arithmetic operations.
int popcount_2(uint64 x)
{
    x-=(x>>1)&m1;//put count of each 2 bits into those 2 bits
    x=(x&m2)+((x>>2)&m2);//put count of each 4 bits into those 4 bits
    x=(x+(x>>4))&m4; //put count of each 8 bits into those 8 bits
    x+=x>>8;//put count of each 16 bits into their lowest 8 bits
    x+=x>>16;
    x+=x>>32;
    return x&0x7f;
}
////This uses fewer arithmetic operations than any other known
//implementation on machines with fast multiplication.
//It uses 12 arithmetic operations, one of which is a multiply.
int popcount_3(uint64 x)
{
    x-=(x>>1)&m1;
    x=(x&m2)+((x>>2)&m2);
    x=(x+(x>>4))&m4;
    return (x*h01)>>56;
}
uint64 popcount_4(uint64 x)
{
    uint64  count;
    for(count=0; x; count++)
    {
        x&=x-1;
    }
    return count;
}
uint64 random()
{
    uint64 r30=RAND_MAX*rand()+rand();
    uint64 s30=RAND_MAX*rand()+rand();
    uint64  t4=rand()&0xf;
    uint64 res=(r30<<34 )+(s30<<4)+t4;
    return res;
}
int main()
{
    int testnum;
    while (true)
    {
        cout<<"enter number of test "<<endl;
        cin>>testnum;
        uint64 x= random();
        switch(testnum)
        {
            case 1: {
                    clock_t start=clock();
                    popcount_1(x);
                    clock_t end=clock();
                    cout<<"execution time of first method"<<start-end<<" "<<endl;
                }
                break;
            case 2: {
                    clock_t start=clock();
                    popcount_2(x);
                    clock_t end=clock();
                    cout<<"execution time of first method"<<start-end<<" "<<endl;
                }
                break;
            case 3: {
                    clock_t start=clock();
                    popcount_3(x);
                    clock_t end=clock();
                    cout<<"execution time of first method"<<start-end<<" "<<endl;
                }
                break;
            case 4: {
                    clock_t start=clock();
                    popcount_4(x);
                    clock_t end=clock();
                    cout<<"execution time of first method"<<start-end<<" "<<endl;
                }
                break;
            default:
                cout<<"it is not correct number "<<endl;
                break;
        }
    }
    return 0;
}

it writes on terminal always zero inspite of which number test i enter,it is clear for me why because 10 or even 20 and 100 operation is not anything for modern computer,but how could i dot such that get if not exact answer,approximation at least?thanks a lot

Answer 1

Just repeat all the tests a large number of times.

The following repeats 1 Mio (1024*1024)2^25 times for each test. You might want to divide the times to get the time in nanoseconds, but for comparison the total numbers would be fine (and easier to read).

int main()
{
    int testnum;
    while (true)
    {
        cout<<"enter number of test "<<endl;
        cin>>testnum;
        uint64 x= random();

        clock_t start=clock();
        switch(testnum)
        {
            case 1: for(unsigned long it=0; it<=(1ul<<26); ++it) popcount_1(x); break;
            case 2: for(unsigned long it=0; it<=(1ul<<26); ++it) popcount_2(x); break;
            case 3: for(unsigned long it=0; it<=(1ul<<26); ++it) popcount_3(x); break;
            case 4: for(unsigned long it=0; it<=(1ul<<26); ++it) popcount_4(x); break;
            default:
                cout<<"it is not correct number "<<endl;
                break;
        }
        clock_t end=clock();
        cout<<"execution time of method " << testnum << ": " << (end-start) <<" "<<endl;
    }
    return 0;
}

Note also fixed start-end to (end-start) 🙂