On 14/10/2016 12:44, Dr. David Alan Gilbert wrote:
>> > +#define QTAILQ_RAW_INSERT_TAIL(head, elm, entry) do {
>> > \
>> > + *((void **) ((char *) (elm) + (entry) + QTAILQ_NEXT_OFFSET)) =
>> > NULL; \
>> > + *((void **) ((char *) (elm) + (entry) + QTAILQ_PREV_OFFSET)) =
>> > \
>> > + *((void **) ((char *) (head) + QTAILQ_LAST_OFFSET));
>> > \
>> > + **((void ***)((char *) (head) + QTAILQ_LAST_OFFSET)) = (elm);
>> > \
>> > + *((void **) ((char *) (head) + QTAILQ_LAST_OFFSET)) =
>> > \
>> > + (void *) ((char *) (elm) + (entry) + QTAILQ_NEXT_OFFSET);
>> > \
>> > +} while (/*CONSTCOND*/0)
> I wonder if there's a simpler way to do this; I'm not sure this works, but
> something like:
>
> struct QTAILQDummy {
> char dummy;
> };
>
> QTAILQ_HEAD(QTAILQRawHead, struct QTAILQDummy)
> typedef QTAILQ_ENTRY(struct QTAILQDummy) QTAILQRawEntry;
>
> #define QTAILQ_RAW_FOREACH(elm, head, entry)
> \
> for ((elm) = ((struct QTAILQRawHead *)head)->tqh_first)
> \
> (elm);
> \
> (elm) =
> \
> (elm) = ((QTAILQRawEntry *)((char *) (elm) + (entry)))->tqh_next
>
> and then I think elm gets declared as a struct QTAILQDummy.
> But it does avoid those FIRST_OFFSET/LAST_OFFSET/NEXT_OFFSET/PREV_OFFSET
> calculations.
Another possibility is a macro like
#define field_at_offset(base, offset, type) \
((type) (((char *) (base)) + (offset)))
so that you can do
*field_at_offset(void **, elm, (entry) + QTAILQ_NEXT_OFFSET) = NULL;
*field_at_offset(void ***, elm, (entry) + QTAILQ_PREV_OFFSET) =
*field_at_offset(void ***, head, QTAILQ_LAST_OFFSET);
**field_at_offset(void ***, head, QTAILQ_LAST_OFFSET) = (elm);
*field_at_offset(void ***, head, QTAILQ_LAST_OFFSET) =
field_at_offset(void **, elm, (entry) + QTAILQ_NEXT_OFFSET);
or something like that (note that I've always used the same type for
next and last, by the way).
Paolo
