qr.h

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/* Ring definitions. */
#define qr(a_type) \
struct { \
 a_type *qre_next; \
 a_type *qre_prev; \
}

/* Ring functions. */
#define qr_new(a_qr, a_field) do { \
 (a_qr)->a_field.qre_next = (a_qr); \
 (a_qr)->a_field.qre_prev = (a_qr); \
} while (0)

#define qr_next(a_qr, a_field) ((a_qr)->a_field.qre_next)

#define qr_prev(a_qr, a_field) ((a_qr)->a_field.qre_prev)

#define qr_before_insert(a_qrelm, a_qr, a_field) do { \
 (a_qr)->a_field.qre_prev = (a_qrelm)->a_field.qre_prev; \
 (a_qr)->a_field.qre_next = (a_qrelm); \
 (a_qr)->a_field.qre_prev->a_field.qre_next = (a_qr); \
 (a_qrelm)->a_field.qre_prev = (a_qr); \
} while (0)

#define qr_after_insert(a_qrelm, a_qr, a_field) \
 do \
 { \
 (a_qr)->a_field.qre_next = (a_qrelm)->a_field.qre_next; \
 (a_qr)->a_field.qre_prev = (a_qrelm); \
 (a_qr)->a_field.qre_next->a_field.qre_prev = (a_qr); \
 (a_qrelm)->a_field.qre_next = (a_qr); \
 } while (0)

#define qr_meld(a_qr_a, a_qr_b, a_field) do { \
 void *t; \
 (a_qr_a)->a_field.qre_prev->a_field.qre_next = (a_qr_b); \
 (a_qr_b)->a_field.qre_prev->a_field.qre_next = (a_qr_a); \
 t = (a_qr_a)->a_field.qre_prev; \
 (a_qr_a)->a_field.qre_prev = (a_qr_b)->a_field.qre_prev; \
 (a_qr_b)->a_field.qre_prev = t; \
} while (0)

/* qr_meld() and qr_split() are functionally equivalent, so there's no need to
 * have two copies of the code. */
#define qr_split(a_qr_a, a_qr_b, a_field) \
 qr_meld((a_qr_a), (a_qr_b), a_field)

#define qr_remove(a_qr, a_field) do { \
 (a_qr)->a_field.qre_prev->a_field.qre_next \
 = (a_qr)->a_field.qre_next; \
 (a_qr)->a_field.qre_next->a_field.qre_prev \
 = (a_qr)->a_field.qre_prev; \
 (a_qr)->a_field.qre_next = (a_qr); \
 (a_qr)->a_field.qre_prev = (a_qr); \
} while (0)

#define qr_foreach(var, a_qr, a_field) \
 for ((var) = (a_qr); \
 (var) != NULL; \
 (var) = (((var)->a_field.qre_next != (a_qr)) \
 ? (var)->a_field.qre_next : NULL))

#define qr_reverse_foreach(var, a_qr, a_field) \
 for ((var) = ((a_qr) != NULL) ? qr_prev(a_qr, a_field) : NULL; \
 (var) != NULL; \
 (var) = (((var) != (a_qr)) \
 ? (var)->a_field.qre_prev : NULL))