What is the fastest/most efficient way to find the highest set bit (msb) in an integer in C?

Question

If I have some integer n, and I want to know the position of the most significant bit (that is, if the least significant bit is on the right, I want to know the position of

Answer 1

thats some kind of binary search, it works with all kinds of (unsigned!) integer types

#include 
#define UINT (unsigned int)
#define UINT_BIT (CHAR_BIT*sizeof(UINT))

int msb(UINT x)
{
    if(0 == x)
        return -1;

    int c = 0;

    for(UINT i=UINT_BIT>>1; 0>=1)
    if(static_cast(x >> i))
    {
        x >>= i;
        c |= i;
    }

    return c;
}

to make complete:

#include 
#define UINT unsigned int
#define UINT_BIT (CHAR_BIT*sizeof(UINT))

int lsb(UINT x)
{
    if(0 == x)
        return -1;

    int c = UINT_BIT-1;

    for(UINT i=UINT_BIT>>1; 0>=1)
    if(static_cast(x << i))
    {
        x <<= i;
        c ^= i;
    }

    return c;
}