recursive.c

#include "clz2.h"

static const int mask[] =  { 0, 8, 12,14 };
static const int magic[] = { 2, 1,  0, 0 };

unsigned clz2(uint32_t x,int c)
{
    if (!x && !c) return 32;

    uint32_t upper = (x >> (16 >> c));
    uint32_t lower = (x & (0xFFFF >> mask[c]));
    if (c == 3) return upper ? magic[upper] : 2 + magic[lower];
    return upper ? clz2(upper, c + 1) : (16 >> (c)) + clz2(lower, c + 1);
}