what does below snippet returns in c

Question

unsigned mystery(int x){               
        unsigned i = 0;
    while(x){
            x = x&(x-1);
            i++;
        }
        return i;                                     
}

I'm thinking this returns powers of '2' till the number we have given.

Possible duplicate of [How to count the number of set bits in a 32-bit integer?](https://stackoverflow.com/questions/109023/how-to-count-the-number-of-set-bits-in-a-32-bit-integer) — Retired Ninja, Jul 09 '18 at 03:22
This is one of my favorites; essentially the algorithm "Counting 1-bits in a sparsely populated word" in the book "Hacker's Delight" by Warren,H.S.,Jr., 2003, which cites Wegner,P.A. "A Technique for Counting Ones in a Binary Computer," Communications of the ACM 3, 5 (May 1960). — phonetagger, Jul 09 '18 at 03:22
See also [Bit Twiddling Hacks](http://graphics.stanford.edu/~seander/bithacks.html) online. — Jonathan Leffler, Jul 09 '18 at 04:18
I'm voting to close this question as off-topic because, while interesting if you've never seen this algorithm before, "questions" of the "puzzle solving" variety like this one will never be searched-for and therefore aren't helpful to SO. — phonetagger, Jul 09 '18 at 13:15
This is not appropriate for Stack Overflow. If you want to see what the code does, *run it*. Don't ask us: ask the ultimate authority: the computer. — Prune, Jul 09 '18 at 15:56

score 5 · Answer 1 · answered Jul 09 '18 at 03:11

It counts the number of set bits in x.

Each time through the loop, the expression x = x&(x-1) will clear the least significant set bit, and it loops until x is zero. i counts the number of iteration until that happens, so it ends up being equal to the number of set bits in the original argument.

This function is usually referred to as "popcount"

what does below snippet returns in c

1 Answers1