/*
 * looking at a loop in x86 assembler
 * (based on 05-machine-control lecture slides from 
 * http://www.cs.cmu.edu/afs/cs/academic/class/15213-f10/www/schedule.html)
 *
 *  $ gcc -m32 -O1 -o loop loop.c
 *  $ ./loop
 *  There are 5 bits that are 1 in 0x4321 .
 *
 *  $ gdb loop
 *  (gdb) disas main
 *  (gdb) disas pcount
 *
 */

#include <stdio.h>

int pcount(unsigned x){
  int result = 0;
  while (x){
    result += x & 0x1;
    x >>= 1;
  }
  return result;
}

int main(){
  unsigned data = 0x4321;
  int ones = pcount(data);
  printf("There are %i bits that are 1 in 0x%x .\n", ones, data);
  return 0;
}