Optimization of the condition in the if-statement-CodePudding

Well I know that the title makes almost no sense but I could not find a better one to explain my question here.

So I've just started doing challenges on LeetCode and I am on the very first steps for now. But one situation confused me.

So I was solving the question named "Number of 1 Bits" which basically gives you an unsigned integer and wants to know how many 1's are in its binary representation.

So first, I've written this code;

class Solution {
public:
int hammingWeight(uint32_t n) {
    
    int answer=0;
    
    while(n>0)
    {
        
        if(n%2)answer  ;
        
        n/=2;
        
    }
    
    return answer;
}
};

Then I realised that it has a runtime of 3 miliseconds.

Then I was trying other solutions to optimize it and I've written the fastest code(i think).

class Solution {
public:
int hammingWeight(uint32_t n) {
    
    int answer=0;
    
    while(n>0)
    {
        
        if(n%2==1)answer  ;
        
        n/=2;
        
    }
    
    return answer;
}
};

So this one had a runtime of 0 miliseconds.

I thought since if(i%2) makes less comparisons, it would be faster.

The only difference is the condition in the "if command".

So why is if(i%2==1) is faster than if(i%2) ?

CodePudding user response：

It's not. Both your code will produce the same machine code.

Your measuring method is wrong, you need to loop that function millions times to get a non-bias result and it will be the same.

The lesson? Don't try to optimize the if statement, in most cases you won't be smarter than the compiler