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sys/tree.h: Red child with black sibling rotations 

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
This commit is contained in:
Sebastian Huber 2021-10-05 15:53:47 +02:00
parent 5f7f27c817
commit eb03ac17f1
1 changed files with 41 additions and 2 deletions
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43
newlib/libc/include/sys/tree.h
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@ -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 an element with 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.
*
* elm (could be the root)
* / \
* BLACK RED (left or right child)
* / \
* 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)) \