From: Arran Cudbard-Bell <a.cudbardb@freeradius.org>
Date: Thu, 2 Apr 2020 15:06:00 +0000 (-0600)
Subject: cursor: Add intersection functions
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=435eab9c491b499efd3f9bfdcbcd2442fa965d85;p=thirdparty%2Ffreeradius-server.git

cursor: Add intersection functions
---

diff --git a/src/lib/util/cursor.c b/src/lib/util/cursor.c
index 994d922984d..5be7d695a50 100644
--- a/src/lib/util/cursor.c
+++ b/src/lib/util/cursor.c
@@ -33,7 +33,7 @@ RCSID("$Id$")
 
 #define NEXT_PTR(_v) ((void **)(((uint8_t *)(_v)) + cursor->offset))
 
-/** Internal function to get the next attribute
+/** Internal function to get the next item
  *
  * @param[in,out] prev	attribute to the one we returned.  May be NULL.
  * @param[in] cursor	to operate on.
@@ -402,6 +402,88 @@ void fr_cursor_merge(fr_cursor_t *cursor, fr_cursor_t *to_append)
 	}
 }
 
+/** Return the first item matching the iterator in cursor a and cursor b
+ *
+ * @param[in] a		First cursor.
+ * @param[in] b		Second cursor.
+ * @return item at the start of the list.
+ */
+void *fr_cursor_intersect_head(fr_cursor_t *a, fr_cursor_t *b)
+{
+	void *a_item, *b_item;
+
+	a_item = fr_cursor_head(a);
+	b_item = fr_cursor_head(b);
+
+	if (a_item == b_item) return a_item;
+
+	return fr_cursor_intersect_next(a, b);
+}
+
+/** Return the next item matching the iterator in cursor a and cursor b
+ *
+ * @param[in] a		First cursor.
+ * @param[in] b		Second cursor.
+ * @return next item in the list.
+ */
+void *fr_cursor_intersect_next(fr_cursor_t *a, fr_cursor_t *b)
+{
+	fr_cursor_iter_t b_iter;
+
+	/*
+	 *	If either of the iterators lack an iterator
+	 *	just use cursor_next...
+	 */
+	if (!a->iter) return fr_cursor_next(b);
+	if (!b->iter) return fr_cursor_next(a);
+
+	/*
+	 *	Both have iterators...
+	 */
+	b_iter = b->iter;
+
+	/*
+	 *	Use a's iterator to select the item to
+	 *	check.
+	 */
+	while ((a->current = cursor_next(&a->prev, a, a->current))) {
+		b->iter = NULL;		/* Disable B's iterator */
+
+		/*
+		 *	Find a in b (the slow way *sigh*)
+		 */
+		while ((b->current = cursor_next(&b->prev, b, b->current)) && (b->current != a->prev));
+
+		/*
+		 *	No more items...
+		 */
+		if (!b->current) {
+			fr_cursor_copy(a, b);
+			return NULL;
+		}
+
+		/*
+		 *	We're now one item before the item
+		 *	returned by a, see if b's iterator
+		 *	returns the same item as a's.
+		 */
+		 b->iter = b_iter;
+		 b->current = cursor_next(&b->prev, b, b->current);
+
+		/*
+		 *	Matched, we're done...
+		 */
+		if (a->current == b->current) return a->current;
+
+		/*
+		 *	Reset b's position to a's and try again.
+		 */
+		fr_cursor_copy(b, a);
+	}
+
+	return NULL;
+}
+
 /** Remove the current item
  *
  * The current item will be set to the one after the item
diff --git a/src/lib/util/cursor.h b/src/lib/util/cursor.h
index 99b82fae69a..559c7af1183 100644
--- a/src/lib/util/cursor.h
+++ b/src/lib/util/cursor.h
@@ -83,6 +83,10 @@ void fr_cursor_insert(fr_cursor_t *cursor, void *v) CC_HINT(nonnull);
 
 void fr_cursor_merge(fr_cursor_t *cursor, fr_cursor_t *to_append) CC_HINT(nonnull);
 
+void *fr_cursor_intersect_head(fr_cursor_t *a, fr_cursor_t *b) CC_HINT(nonnull);
+
+void *fr_cursor_intersect_next(fr_cursor_t *a, fr_cursor_t *b) CC_HINT(nonnull);
+
 void *fr_cursor_remove(fr_cursor_t *cursor) CC_HINT(nonnull);
 
 void *fr_cursor_replace(fr_cursor_t *cursor, void *r) CC_HINT(nonnull);