Add specialized rotations RB_RED_ROTATE_LEFT() and RB_RED_ROTATE_RIGHT() which
may be used if we rotate a red child which has a black sibling. Such a red
node must have at least two child nodes so that the following red-black tree
invariant is fulfilled:
Every path from a given node to any of its descendant NULL nodes goes through
the same number of black nodes.
PARENT
/ \
BLACK RED
/ \
BLACK BLACK
---
newlib/libc/include/sys/tree.h | 43 ++++++++++++++++++++++++++++++++--
1 file changed, 41 insertions(+), 2 deletions(-)
diff --git a/newlib/libc/include/sys/tree.h b/newlib/libc/include/sys/tree.h
index f6190f7f4..7a3b55bdf 100644
--- a/newlib/libc/include/sys/tree.h
+++ b/newlib/libc/include/sys/tree.h
@@ -412,6 +412,45 @@ struct {
\
RB_AUGMENT(right); \
} while (/*CONSTCOND*/ 0)
+/*
+ * The RB_RED_ROTATE_LEFT() and RB_RED_ROTATE_RIGHT() rotations are specialized
+ * versions of RB_ROTATE_LEFT() and RB_ROTATE_RIGHT() which may be used if we
+ * rotate a red child element which has a black sibling. Such a red node must
+ * have at least two child nodes so that the following red-black tree invariant
+ * is fulfilled:
+ *
+ * Every path from a given node to any of its descendant NULL nodes goes
+ * through the same number of black nodes.
+ *
+ * parent
+ * / \
+ * BLACK RED (elm)
+ * / \
+ * BLACK BLACK
+ */
+
+#define RB_RED_ROTATE_LEFT(head, elm, tmp, field) do { \
+ (tmp) = RB_RIGHT(elm, field); \
+ RB_RIGHT(elm, field) = RB_LEFT(tmp, field); \
+ RB_SET_PARENT(RB_RIGHT(elm, field), elm, field); \
+ RB_SET_PARENT(tmp, RB_PARENT(elm, field), field); \
+ RB_SWAP_CHILD(head, elm, tmp, field); \
+ RB_LEFT(tmp, field) = (elm); \
+ RB_SET_PARENT(elm, tmp, field); \
+ RB_AUGMENT(elm); \
+} while (/*CONSTCOND*/ 0)
+
+#define RB_RED_ROTATE_RIGHT(head, elm, tmp, field) do {
\
+ (tmp) = RB_LEFT(elm, field); \
+ RB_LEFT(elm, field) = RB_RIGHT(tmp, field); \
+ RB_SET_PARENT(RB_LEFT(elm, field), elm, field); \
+ RB_SET_PARENT(tmp, RB_PARENT(elm, field), field); \
+ RB_SWAP_CHILD(head, elm, tmp, field); \
+ RB_RIGHT(tmp, field) = (elm); \
+ RB_SET_PARENT(elm, tmp, field); \
+ RB_AUGMENT(elm); \
+} while (/*CONSTCOND*/ 0)
+
/* Generates prototypes and inline functions */
#define RB_PROTOTYPE(name, type, field, cmp)
\
RB_PROTOTYPE_INTERNAL(name, type, field, cmp,)
@@ -526,7 +565,7 @@ name##_RB_REMOVE_COLOR(struct name *head, struct type
*parent) \
tmp = RB_RIGHT(parent, field); \
if (RB_COLOR(tmp, field) == RB_RED) { \
RB_SET_BLACKRED(tmp, parent, field); \
- RB_ROTATE_LEFT(head, parent, tmp, field);\
+ RB_RED_ROTATE_LEFT(head, parent, tmp, field); \
tmp = RB_RIGHT(parent, field); \
} \
if (RB_ISRED(RB_RIGHT(tmp, field), field)) \
@@ -552,7 +591,7 @@ name##_RB_REMOVE_COLOR(struct name *head, struct type
*parent) \
tmp = RB_LEFT(parent, field); \
if (RB_COLOR(tmp, field) == RB_RED) { \
RB_SET_BLACKRED(tmp, parent, field); \
- RB_ROTATE_RIGHT(head, parent, tmp, field);\
+ RB_RED_ROTATE_RIGHT(head, parent, tmp, field); \
tmp = RB_LEFT(parent, field); \
} \
if (RB_ISRED(RB_LEFT(tmp, field), field)) \
--
2.26.2
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