/* Demonstrate atomic exchange         */

#include <stdio.h>

/* Code to atomic exchange */
static void
exchange(lock, val, out) /* Atomic exchange value->memory */
unsigned int *lock; /* Points to location to swap */
unsigned int val;   /* New value to store in swap location */
unsigned int *out;  /* Points to where to store old value */
{
    asm("swap [%i0], %i1");
    asm ("st %i1, [%i2]");
}

int Lock = 0;

int main()
{
int OldLock;

 exchange(&Lock, 1, &OldLock);
 printf("Old Lock value %d\n", OldLock);
 exchange(&Lock, 1, &OldLock);
 printf("Old Lock value %d\n", OldLock);
 return(0);
}

#ifdef HERES_THE_OUTPUT
Old Lock value 0
Old Lock value 1
#endif