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

#define MAXLEN 53

unsigned int bitCount(unsigned long num);
uint8_t doesItFit(unsigned long num);

void main () {
    int num = 0b10100000;
    unsigned long bigNum = 18446744073709551615; // 2^64-1

    printf(
        "Fit? Small: %d, Big: %d\n", 
        doesItFit(num),
        doesItFit(bigNum)
    );
}

unsigned int  bitCount(unsigned long num) {
    unsigned int bits = 0;

    while (num) {
        bits++;
        num >>= 1;
    }

    return bits;
}

uint8_t doesItFit (unsigned long num) {
    num = num >> __builtin_ctz(num);
    unsigned int numBits = bitCount(num);
    return numBits <= MAXLEN ? 1 : 0;
}