#include <stdio.h>
#include <stdlib.h>
#include <setjmp.h>

/* State used in two functions. */
jmp_buf func_state, main_state;

/* Random message. */
const char *msg;

void func()
{
	/* Meaningless counter. */
	int m;

	/* setjmp() return value. */
	int ret;

	/* This copies the registers to func_state, and returns 0.  When
	   the register values are restored by longjmp, the PC is changed
	   so this function returns again.  It's return value is specified
	   in the longjmp call. */
	ret = setjmp(func_state);
	if(ret == 0) {
		/* First time setjmp() returns. */
		printf("Begin func()\n");
		m = 1;
		longjmp(main_state, 1);
	}

	/* We reach here when setjmp() returns as a result of a register
	   restore by longjmp().  Do a bit, depending on the return value
	   sent by the restore, then restore the registers in main_state
	   which will return control there. */
	printf("func: ret = %d, m = %d, msg = %s\n", ret, m, msg);
	if(ret == 1) m *= 2;
	longjmp(main_state, 1);

	/* Control never reaches this point. */
	printf("func done\n");
}

main()
{
	/* Iteration counter */
	int n = 0;

	/* A set of messages to store in rotation. */
	const char *msgs[] = { "Moonbat", "Ringworm", "Northstar",
			       "Swamp", "Polarbear", "Snakeoil" };

	/* Save our registers in main_state, then, on the original
	   save, call the function. */
	if(!setjmp(main_state)) func();

	/* On restores from the function, set a message and go back there.
	   Do this 10 times, then stop. */
	msg = msgs[n%6];
	if(n++ < 10) longjmp(func_state, n%2 + 1);

	printf("Done\n");

	exit(0);
}

/* Remember this:
      setjmp()  can return any number of times.
      longjmp() the longjmp call does not return; instead, it makes 
                last setjmp() on the same buffer return again.
*/