#include <stdio.h>

#define FibCtor { 0, 0, NULL }
typedef struct {
	int fn1, fn2;
	void * next;
} Fib;

int fib( Fib * f ) {
	if ( __builtin_expect(f->next != 0, 1) ) goto *f->next;
  s1:
	f->fn1 = 0;
	f->next = &&s2;
	return f->fn1;
  s2:
	f->fn2 = f->fn1;
	f->fn1 = 1;
	f->next = &&s3;
	return f->fn1;
  s3:;
	int fn = f->fn1 + f->fn2;
	f->fn2 = f->fn1;
	f->fn1 = fn;
	return fn;
}
int main() {
	Fib f1 = FibCtor, f2 = FibCtor;
	for ( int i = 0; i < 10; i += 1 ) {
		printf( "%d %d\n", fib( &f1 ), fib( &f2 ) );
	}
}

// Local Variables: //
// tab-width: 4 //
// compile-command: "gcc-8 Fib1.c" //
// End: //