#include <stdio.h>
#include <stdlib.h>
/* co-routines in (gnu) c

   inspired by http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html
   instead of using an offet to a jump table, it's possible to use
   an offset to a code label in GNU C

   labels as values are defined here: 
   http://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html
 
   like sgtathams code, we store an offset to jump back into
   the function but we use a direct jmp instead of an internal jump table.   
*/

/* the preprocessor works in mysterious ways */

#define __NAME__    __LABEL__(__LINE__)
#define __LABEL__(x) __LABEL2__(x)
#define __LABEL2__(x) __next##__##x

typedef unsigned int __offset__;

#define CORO_STRUCT(x) typedef struct {__offset__ __state__; struct x;}

#define CORO_MALLOC(t,cr) \
    t *cr = malloc(sizeof(t));\
    cr -> __state__ = 0

#define CORO_STATIC(cr,t,in)  \
    static t (cr) = {0,in}; \
    CORO_INIT(cr)

#define CORO_INIT(cr) \
    goto *(&&__init__ + (cr).__state__); \
    __init__: 

/* use offsets instead of label addresses, to
   make code relocatable
*/
#define YIELD(cr, ...)  { \
    (cr).__state__ =  &&__NAME__ - &&__init__; \
    return __VA_ARGS__; \
    } __NAME__:


/* possible cleanup code */
#define FAIL(cr) {}


CORO_STRUCT({int i;})  foo_cr;

/* example coroutine */
int foo_static() {
    CORO_STATIC(cr,foo_cr, {10});
    while (cr.i--) {
        YIELD(cr,cr.i);
    }
    return 0;
}

int foo_dynamic(foo_cr *cr) {
    CORO_INIT(*cr);
    cr->i = 9;
    while ((cr->i)--) {
        YIELD(*cr,cr->i);
    }
    return 0;
}

int main () {
    int a;

    while (1) {
        a = foo_static();
        if (a <= 0) break;
        printf("-%d\n",a);
    }
   
    CORO_MALLOC(foo_cr,cr); 
    while (1) {
        a = foo_dynamic(cr);
        if (a <= 0) break;
        printf("%d\n",a);
    }
    free(cr);
    return 0;
}