From 8e4fd0a138830c5cc2a14480689f3d22a27ceaff Mon Sep 17 00:00:00 2001
From: Jason Evans <jasone@FreeBSD.org>
Date: Fri, 28 Dec 2007 07:03:26 +0000
Subject: [PATCH] Implement RB_PREV() AND RB_FOREACH_REVERSE().

---
 share/man/man3/tree.3 | 12 ++++++++++--
 sys/sys/tree.h        | 29 +++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/share/man/man3/tree.3 b/share/man/man3/tree.3
index 78ba4b0c4621..aa53eb134c73 100644
--- a/share/man/man3/tree.3
+++ b/share/man/man3/tree.3
@@ -30,7 +30,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 17, 2006
+.Dd December 27, 2007
 .Dt TREE 3
 .Os
 .Sh NAME
@@ -61,6 +61,7 @@
 .Nm RB_ROOT ,
 .Nm RB_EMPTY ,
 .Nm RB_NEXT ,
+.Nm RB_PREV ,
 .Nm RB_MIN ,
 .Nm RB_MAX ,
 .Nm RB_FIND ,
@@ -69,6 +70,7 @@
 .Nm RB_RIGHT ,
 .Nm RB_PARENT ,
 .Nm RB_FOREACH ,
+.Nm RB_FOREACH_REVERSE ,
 .Nm RB_INIT ,
 .Nm RB_INSERT ,
 .Nm RB_REMOVE
@@ -117,6 +119,8 @@
 .Ft "struct TYPE *"
 .Fn RB_NEXT NAME "RB_HEAD *head" "struct TYPE *elm"
 .Ft "struct TYPE *"
+.Fn RB_PREV NAME "RB_HEAD *head" "struct TYPE *elm"
+.Ft "struct TYPE *"
 .Fn RB_MIN NAME "RB_HEAD *head"
 .Ft "struct TYPE *"
 .Fn RB_MAX NAME "RB_HEAD *head"
@@ -131,6 +135,7 @@
 .Ft "struct TYPE *"
 .Fn RB_PARENT "struct TYPE *elm" "RB_ENTRY NAME"
 .Fn RB_FOREACH VARNAME NAME "RB_HEAD *head"
+.Fn RB_FOREACH_REVERSE VARNAME NAME "RB_HEAD *head"
 .Ft void
 .Fn RB_INIT "RB_HEAD *head"
 .Ft "struct TYPE *"
@@ -433,14 +438,17 @@ The
 .Fn RB_ROOT ,
 .Fn RB_MIN ,
 .Fn RB_MAX ,
+.Fn RB_NEXT ,
 and
-.Fn RB_NEXT
+.Fn RB_PREV
 macros can be used to traverse the tree:
 .Pp
 .Dl "for (np = RB_MIN(NAME, &head); np != NULL; np = RB_NEXT(NAME, &head, np))"
 .Pp
 Or, for simplicity, one can use the
 .Fn RB_FOREACH
+or
+.Fn RB_FOREACH_REVERSE
 macro:
 .Bd -ragged -offset indent
 .Fn RB_FOREACH np NAME head
diff --git a/sys/sys/tree.h b/sys/sys/tree.h
index 3af9a2b14406..54ea6da5cc71 100644
--- a/sys/sys/tree.h
+++ b/sys/sys/tree.h
@@ -390,6 +390,7 @@ attr struct type *name##_RB_INSERT(struct name *, struct type *);	\
 attr struct type *name##_RB_FIND(struct name *, struct type *);		\
 attr struct type *name##_RB_NFIND(struct name *, struct type *);	\
 attr struct type *name##_RB_NEXT(struct type *);			\
+attr struct type *name##_RB_PREV(struct type *);			\
 attr struct type *name##_RB_MINMAX(struct name *, int);			\
 									\
 
@@ -682,6 +683,28 @@ name##_RB_NEXT(struct type *elm)					\
 	return (elm);							\
 }									\
 									\
+/* ARGSUSED */								\
+attr struct type *							\
+name##_RB_PREV(struct type *elm)					\
+{									\
+	if (RB_LEFT(elm, field)) {					\
+		elm = RB_LEFT(elm, field);				\
+		while (RB_RIGHT(elm, field))				\
+			elm = RB_RIGHT(elm, field);			\
+	} else {							\
+		if (RB_PARENT(elm, field) &&				\
+		    (elm == RB_RIGHT(RB_PARENT(elm, field), field)))	\
+			elm = RB_PARENT(elm, field);			\
+		else {							\
+			while (RB_PARENT(elm, field) &&			\
+			    (elm == RB_LEFT(RB_PARENT(elm, field), field)))\
+				elm = RB_PARENT(elm, field);		\
+			elm = RB_PARENT(elm, field);			\
+		}							\
+	}								\
+	return (elm);							\
+}									\
+									\
 attr struct type *							\
 name##_RB_MINMAX(struct name *head, int val)				\
 {									\
@@ -705,6 +728,7 @@ name##_RB_MINMAX(struct name *head, int val)				\
 #define RB_FIND(name, x, y)	name##_RB_FIND(x, y)
 #define RB_NFIND(name, x, y)	name##_RB_NFIND(x, y)
 #define RB_NEXT(name, x, y)	name##_RB_NEXT(y)
+#define RB_PREV(name, x, y)	name##_RB_PREV(y)
 #define RB_MIN(name, x)		name##_RB_MINMAX(x, RB_NEGINF)
 #define RB_MAX(name, x)		name##_RB_MINMAX(x, RB_INF)
 
@@ -713,4 +737,9 @@ name##_RB_MINMAX(struct name *head, int val)				\
 	     (x) != NULL;						\
 	     (x) = name##_RB_NEXT(x))
 
+#define RB_FOREACH_REVERSE(x, name, head)				\
+	for ((x) = RB_MAX(name, head);					\
+	     (x) != NULL;						\
+	     (x) = name##_RB_PREV(x))
+
 #endif	/* _SYS_TREE_H_ */