TODO: ffs/clz
64 bit variants of everything
TODO: examples from X for clz/ctz
TODO: arithmetic right shift
TODO: bit reversal
TODO: template/generic functions for x32/x64 and so on
TODO: generalised shift
unsigned long gensh(unsigned long v, int x) {
int a, b;
    a = (v << x) & -(((unsigned int)x) < 32);
    x = -x;
    b = (v >> x) & -(((unsigned int)x) < 32);
    return a|b;
}