cnt.c

#include <stdio.h>
#include <stdint.h>

#define TZCNTQ(DST, SRC)        \
    do {                        \
        asm (                   \
            "tzcntq %1, %0;"    \
            : "=r" (DST)        \
            : "r" (SRC)         \
            );                  \
    } while (0)

#define LZCNTQ(DST, SRC)        \
    do {                        \
        asm volatile (          \
            "lzcntq %1, %0;"    \
            : "=r" (DST)        \
            : "r" (SRC)         \
            );                  \
    } while (0)

uint64_t
tzcntq(uint64_t num)
{
    uint64_t ret;
    TZCNTQ(ret, num);
    return ret;
}

uint64_t
lzcntq(uint64_t num)
{
    uint64_t ret;
    LZCNTQ(ret, num);
    return ret;
}

int
main(int argc, char *argv[])
{
    for (int i = 0; i < 64; i++) {
        uint64_t n = 1;
        n <<= i;
        uint64_t cnt;

        //cnt = __builtin_clzll(n);
        cnt = lzcntq(n);
        //LZCNTQ(n, cnt);
        printf("n = %llx, cnt = %llu\n", n, cnt);
    }
    
    return 0;
}