Jumping like Duff

duff.c

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

// Found in the slow clone of Cilk procedures
// An application of Duff's device to jump directly into the middle of code
// See Cilk 5.4.6 Reference Manual
// 
// The same technique can be used to implement stack-based coroutines 
// See Simon Tatham's Coroutines in C

void func(int i)
{
	switch (i) {
	case 0: goto _0;
	case 1: goto _1;
	case 2: goto _2;
	}

	if (0) { _0: printf("Hi 0!\n"); }
	if (0) { _1: printf("Hi 1!\n"); }
	if (0) { _2: printf("Hi 2!\n"); }
}

int main(void)
{
	int i;

	for (i = 0; i < 3; i++)
		func(i);

	return 0;
}