gistfile1.txt

/tmp
➜ ./a.out
0
1
0
1
0
1

pow2.c

#include <stdio.h>

int p2(unsigned int n) {
  int r;
  __asm__( "popcnt %1, %0; "
            : "=r" (r)
            : "r" (n)
            : "%rdi" );
  return (r == 1);
}

int main() {
  printf("%d\n",p2(0));
  printf("%d\n",p2(2));
  printf("%d\n",p2(3));
  printf("%d\n",p2(4));
  printf("%d\n",p2(255));
  printf("%d\n",p2(256));
  return 0;
}