Swap values of two integer variables without introducing the third one - inline assembly abuse edition

swap.c

/**
 * PROBLEM: 
 *    Swap values of two integer
 *    variables without introducing
 *    the third one
 *
 * $ gcc -o swap swap.c
 * $ chmod +x swap
 * $ ./swap
 *
 */

#include <stdio.h>

int main() {
  int a = 69;
  int b = 420;
  
  printf("a = %d; b = %d", a, b);
  
  asm ("xchg %0, %1\n" : "=r" (a) : "r" (b));
  
  printf("a = %d; b = %d", a, b);
  
  return 0;
}