Commit 2120d7f5 authored by Doug Moore's avatar Doug Moore
Browse files

rb_tree: fine-tune rebalancing code

Change parts of RB_INSERT_COLOR and RB_REMOVE_COLOR to reduce the
number of operations, by, in some cases, flipping two color bits at a
time instead of flipping each individually, in separate operations,
and by using a switch statement to replace a sequence of if-elses.
Rewrite RB_SET_PARENT to generate fewer instructions.  These changes
reduce the code size by over 100 bytes on some architectures.

Also, allow RB users to define a preprocessor symbol to generate
RB_REMOVE_COLOR code that matches the implementation described in the
original weak-AVL paper in one particular case, instead of the still
correct, but slightly more efficient implementation of that case
currently implemented.

Reviewed by:	alc
MFC after:	3 weeks
Differential Revision:	https://reviews.freebsd.org/D35524
parent 0aa15077
......@@ -340,6 +340,7 @@ struct { \
#define RB_RED_MASK ((__uintptr_t)3)
#define RB_FLIP_LEFT(elm, field) (RB_BITS(elm, field) ^= RB_RED_L)
#define RB_FLIP_RIGHT(elm, field) (RB_BITS(elm, field) ^= RB_RED_R)
#define RB_FLIP_ALL(elm, field) (RB_BITS(elm, field) ^= RB_RED_MASK)
#define RB_RED_LEFT(elm, field) ((RB_BITS(elm, field) & RB_RED_L) != 0)
#define RB_RED_RIGHT(elm, field) ((RB_BITS(elm, field) & RB_RED_R) != 0)
#define RB_PARENT(elm, field) ((__typeof(RB_UP(elm, field))) \
......@@ -348,8 +349,8 @@ struct { \
#define RB_EMPTY(head) (RB_ROOT(head) == NULL)
#define RB_SET_PARENT(dst, src, field) do { \
RB_BITS(dst, field) &= RB_RED_MASK; \
RB_BITS(dst, field) |= (__uintptr_t)src; \
RB_BITS(dst, field) = (__uintptr_t)src | \
(RB_BITS(dst, field) & RB_RED_MASK); \
} while (/*CONSTCOND*/ 0)
#define RB_SET(elm, parent, field) do { \
......@@ -487,13 +488,14 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
continue; \
} \
if (!RB_RED_RIGHT(elm, field)) { \
RB_FLIP_LEFT(elm, field); \
/* coverity[uninit_use] */ \
RB_ROTATE_LEFT(head, elm, child, field);\
if (RB_RED_LEFT(child, field)) \
RB_FLIP_RIGHT(elm, field); \
else if (RB_RED_RIGHT(child, field)) \
if (RB_RED_RIGHT(child, field)) \
RB_FLIP_LEFT(parent, field); \
if (RB_RED_LEFT(child, field)) \
RB_FLIP_ALL(elm, field); \
else \
RB_FLIP_LEFT(elm, field); \
elm = child; \
} \
RB_ROTATE_RIGHT(head, parent, elm, field); \
......@@ -509,13 +511,14 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
continue; \
} \
if (!RB_RED_LEFT(elm, field)) { \
RB_FLIP_RIGHT(elm, field); \
/* coverity[uninit_use] */ \
RB_ROTATE_RIGHT(head, elm, child, field);\
if (RB_RED_RIGHT(child, field)) \
RB_FLIP_LEFT(elm, field); \
else if (RB_RED_LEFT(child, field)) \
if (RB_RED_LEFT(child, field)) \
RB_FLIP_RIGHT(parent, field); \
if (RB_RED_RIGHT(child, field)) \
RB_FLIP_ALL(elm, field); \
else \
RB_FLIP_RIGHT(elm, field); \
elm = child; \
} \
RB_ROTATE_LEFT(head, parent, elm, field); \
......@@ -525,6 +528,17 @@ name##_RB_INSERT_COLOR(struct name *head, struct type *elm) \
} \
}
#ifndef RB_STRICT_HST
/*
* In REMOVE_COLOR, the HST paper, in figure 3, in the single-rotate case, has
* 'parent' with one higher rank, and then reduces its rank if 'parent' has
* become a leaf. This implementation always has the parent in its new position
* with lower rank, to avoid the leaf check. Define RB_STRICT_HST to 1 to get
* the behavior that HST describes.
*/
#define RB_STRICT_HST 0
#endif
#define RB_GENERATE_REMOVE_COLOR(name, type, field, attr) \
attr void \
name##_RB_REMOVE_COLOR(struct name *head, \
......@@ -539,7 +553,7 @@ name##_RB_REMOVE_COLOR(struct name *head, \
if (parent == NULL) \
return; \
} \
do { \
do { \
if (RB_LEFT(parent, field) == elm) { \
if (!RB_RED_LEFT(parent, field)) { \
RB_FLIP_LEFT(parent, field); \
......@@ -551,24 +565,36 @@ name##_RB_REMOVE_COLOR(struct name *head, \
continue; \
} \
sib = RB_RIGHT(parent, field); \
if ((~RB_BITS(sib, field) & RB_RED_MASK) == 0) {\
RB_BITS(sib, field) &= ~RB_RED_MASK; \
switch (RB_BITS(sib, field) & RB_RED_MASK) { \
case RB_RED_MASK: \
RB_FLIP_ALL(sib, field); \
elm = parent; \
continue; \
} \
RB_FLIP_RIGHT(sib, field); \
if (RB_RED_LEFT(sib, field)) \
RB_FLIP_LEFT(parent, field); \
else if (!RB_RED_RIGHT(sib, field)) { \
RB_FLIP_LEFT(parent, field); \
case RB_RED_R: \
elm = RB_LEFT(sib, field); \
RB_ROTATE_RIGHT(head, sib, elm, field); \
if (RB_RED_RIGHT(elm, field)) \
RB_FLIP_LEFT(sib, field); \
if (RB_RED_LEFT(elm, field)) \
RB_FLIP_RIGHT(parent, field); \
RB_FLIP_ALL(parent, field); \
else \
RB_FLIP_LEFT(parent, field); \
if (RB_RED_RIGHT(elm, field)) \
RB_FLIP_ALL(sib, field); \
else \
RB_FLIP_RIGHT(sib, field); \
RB_BITS(elm, field) |= RB_RED_MASK; \
sib = elm; \
break; \
case RB_RED_L: \
if (RB_STRICT_HST && elm != NULL) { \
RB_FLIP_RIGHT(parent, field); \
RB_FLIP_ALL(sib, field); \
break; \
} \
RB_FLIP_LEFT(parent, field); \
/* FALLTHROUGH */ \
default: \
RB_FLIP_RIGHT(sib, field); \
break; \
} \
RB_ROTATE_LEFT(head, parent, sib, field); \
} else { \
......@@ -582,24 +608,36 @@ name##_RB_REMOVE_COLOR(struct name *head, \
continue; \
} \
sib = RB_LEFT(parent, field); \
if ((~RB_BITS(sib, field) & RB_RED_MASK) == 0) {\
RB_BITS(sib, field) &= ~RB_RED_MASK; \
switch (RB_BITS(sib, field) & RB_RED_MASK) { \
case RB_RED_MASK: \
RB_FLIP_ALL(sib, field); \
elm = parent; \
continue; \
} \
RB_FLIP_LEFT(sib, field); \
if (RB_RED_RIGHT(sib, field)) \
RB_FLIP_RIGHT(parent, field); \
else if (!RB_RED_LEFT(sib, field)) { \
RB_FLIP_RIGHT(parent, field); \
case RB_RED_L: \
elm = RB_RIGHT(sib, field); \
RB_ROTATE_LEFT(head, sib, elm, field); \
if (RB_RED_LEFT(elm, field)) \
RB_FLIP_RIGHT(sib, field); \
if (RB_RED_RIGHT(elm, field)) \
RB_FLIP_LEFT(parent, field); \
RB_FLIP_ALL(parent, field); \
else \
RB_FLIP_RIGHT(parent, field); \
if (RB_RED_LEFT(elm, field)) \
RB_FLIP_ALL(sib, field); \
else \
RB_FLIP_LEFT(sib, field); \
RB_BITS(elm, field) |= RB_RED_MASK; \
sib = elm; \
break; \
case RB_RED_R: \
if (RB_STRICT_HST && elm != NULL) { \
RB_FLIP_LEFT(parent, field); \
RB_FLIP_ALL(sib, field); \
break; \
} \
RB_FLIP_RIGHT(parent, field); \
/* FALLTHROUGH */ \
default: \
RB_FLIP_LEFT(sib, field); \
break; \
} \
RB_ROTATE_RIGHT(head, parent, sib, field); \
} \
......
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