How To Find The Leading Number Of Zero's In a Number using C

Question

for example,if i have number 64,then its binary representation would be 0000 0000 0000 0000 0000 0000 0100 0000 so leading number of zero\'s is 25. remember i have to calculate

Answer 1

I just found this problem at the top of the search results and this code:

int pop(unsigned x) {
    unsigned n;
    n = (x >> 1) & 033333333333;
    x = x - n;
    n = (n >> 1) & 033333333333;
    x = x - n;
    x = (x + (x >> 3)) & 030707070707;
    return x % 63;
}

int nlz(unsigned x) {
    x = x | (x >> 1);
    x = x | (x >> 2);
    x = x | (x >> 4);
    x = x | (x >> 8);
    x = x | (x >>16);
    return pop(~x);
}

where pop counts 1 bits, is several times faster than the first (upvoted) answer.

I didn't notice, question was about 64 bits numbers, so here:

int nlz(unsigned long x) {
    unsigned long y;
    long n, c;
    n = 64;
    c = 32;
    do {
        y = x >> c;
        if (y != 0) {
            n = n - c;
            x = y;
        }
        c = c >> 1;
    } while (c != 0);
    return n - x;
}

is a 64 bits algorithm, again several times faster than the mentioned above.