Mine

static inline int
ls1bit32 (unsigned int x)
{
    int b = 31, s;

    s = 16;
    if (x << 16 == 0)
        s = 0;
    b -= s;
    x <<= s;
    s = 8;
    if (x << 8 == 0)
        s = 0;
    b -= s;
    x <<= s;
    s = 4;
    if (x << 4 == 0)
        s = 0;
    b -= s;
    x <<= s;
    s = 2;
    if (x << 2 == 0)
        s = 0;
    b -= s;
    x <<= s;
    s = 1;
    if (x << 1 == 0)
        s = 0;
    b -= s;

    return b;
}