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[apple/xnu.git] / bsd / hfs / hfscommon / headers / RedBlackTree.h
diff --git a/bsd/hfs/hfscommon/headers/RedBlackTree.h b/bsd/hfs/hfscommon/headers/RedBlackTree.h
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+/*
+ * Copyright (c) 2009 Apple Inc. All rights reserved.
+ *
+ * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
+ * 
+ * This file contains Original Code and/or Modifications of Original Code
+ * as defined in and that are subject to the Apple Public Source License
+ * Version 2.0 (the 'License'). You may not use this file except in
+ * compliance with the License. The rights granted to you under the License
+ * may not be used to create, or enable the creation or redistribution of,
+ * unlawful or unlicensed copies of an Apple operating system, or to
+ * circumvent, violate, or enable the circumvention or violation of, any
+ * terms of an Apple operating system software license agreement.
+ * 
+ * Please obtain a copy of the License at
+ * http://www.opensource.apple.com/apsl/ and read it before using this file.
+ * 
+ * The Original Code and all software distributed under the License are
+ * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+ * Please see the License for the specific language governing rights and
+ * limitations under the License.
+ * 
+ * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
+ */
+
+/******************************************************************************
+ *
+ * Copyright (C) 2008 Jason Evans <jasone@FreeBSD.org>.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice(s), this list of conditions and the following disclaimer
+ *    unmodified other than the allowable addition of one or more
+ *    copyright notices.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice(s), this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+ * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+ * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ ******************************************************************************
+ *
+ * cpp macro implementation of left-leaning red-black trees.
+ *
+ * Usage:
+ *
+ *   (Optional, see assert(3).)
+ *   #define NDEBUG
+ *
+ *   (Required.)
+ *   #include <assert.h>
+ *   #include <rb.h>
+ *   ...
+ *
+ * All operations are done non-recursively.  Parent pointers are not used, and
+ * color bits are stored in the least significant bit of right-child pointers,
+ * thus making node linkage as compact as is possible for red-black trees.
+ *
+ * Some macros use a comparison function pointer, which is expected to have the
+ * following prototype:
+ *
+ *   int (a_cmp *)(a_type *a_node, a_type *a_other);
+ *                         ^^^^^^
+ *                      or a_key
+ *
+ * Interpretation of comparision function return values:
+ *
+ *   -1 : a_node <  a_other
+ *    0 : a_node == a_other
+ *    1 : a_node >  a_other
+ *
+ * In all cases, the a_node or a_key macro argument is the first argument to the
+ * comparison function, which makes it possible to write comparison functions
+ * that treat the first argument specially.
+ *
+ ******************************************************************************/
+
+#ifndef RB_H_
+#define        RB_H_
+
+#define        RB_COMPACT
+#ifdef RB_COMPACT
+/* Node structure. */
+#define        rb_node(a_type)                                                 \
+struct {                                                               \
+    a_type *rbn_left;                                                  \
+    a_type *rbn_right_red;                                             \
+}
+#else
+#define        rb_node(a_type)                                                 \
+struct {                                                               \
+    a_type *rbn_left;                                                  \
+    a_type *rbn_right;                                                 \
+    bool rbn_red;                                                      \
+}
+#endif
+
+/* Root structure. */
+#define        rb_tree(a_type)                                                 \
+struct {                                                               \
+    a_type *rbt_root;                                                  \
+    a_type rbt_nil;                                                    \
+}
+
+/* Left accessors. */
+#define        rbp_left_get(a_type, a_field, a_node)                           \
+    ((a_node)->a_field.rbn_left)
+#define        rbp_left_set(a_type, a_field, a_node, a_left) do {              \
+    (a_node)->a_field.rbn_left = a_left;                               \
+} while (0)
+
+#ifdef RB_COMPACT
+/* Right accessors. */
+#define        rbp_right_get(a_type, a_field, a_node)                          \
+    ((a_type *) (((intptr_t) (a_node)->a_field.rbn_right_red)          \
+      & ((ssize_t)-2)))
+#define        rbp_right_set(a_type, a_field, a_node, a_right) do {            \
+    (a_node)->a_field.rbn_right_red = (a_type *) (((uintptr_t) a_right)        \
+      | (((uintptr_t) (a_node)->a_field.rbn_right_red) & ((size_t)1)));        \
+} while (0)
+
+/* Color accessors. */
+#define        rbp_red_get(a_type, a_field, a_node)                            \
+    ((bool) (((uintptr_t) (a_node)->a_field.rbn_right_red)             \
+      & ((size_t)1)))
+#define        rbp_color_set(a_type, a_field, a_node, a_red) do {              \
+    (a_node)->a_field.rbn_right_red = (a_type *) ((((intptr_t)         \
+      (a_node)->a_field.rbn_right_red) & ((ssize_t)-2))                        \
+      | ((ssize_t)a_red));                                             \
+} while (0)
+#define        rbp_red_set(a_type, a_field, a_node) do {                       \
+    (a_node)->a_field.rbn_right_red = (a_type *) (((uintptr_t)         \
+      (a_node)->a_field.rbn_right_red) | ((size_t)1));                 \
+} while (0)
+#define        rbp_black_set(a_type, a_field, a_node) do {                     \
+    (a_node)->a_field.rbn_right_red = (a_type *) (((intptr_t)          \
+      (a_node)->a_field.rbn_right_red) & ((ssize_t)-2));               \
+} while (0)
+#else
+/* Right accessors. */
+#define        rbp_right_get(a_type, a_field, a_node)                          \
+    ((a_node)->a_field.rbn_right)
+#define        rbp_right_set(a_type, a_field, a_node, a_right) do {            \
+    (a_node)->a_field.rbn_right = a_right;                             \
+} while (0)
+
+/* Color accessors. */
+#define        rbp_red_get(a_type, a_field, a_node)                            \
+    ((a_node)->a_field.rbn_red)
+#define        rbp_color_set(a_type, a_field, a_node, a_red) do {              \
+    (a_node)->a_field.rbn_red = (a_red);                               \
+} while (0)
+#define        rbp_red_set(a_type, a_field, a_node) do {                       \
+    (a_node)->a_field.rbn_red = true;                          \
+} while (0)
+#define        rbp_black_set(a_type, a_field, a_node) do {                     \
+    (a_node)->a_field.rbn_red = false;                         \
+} while (0)
+#endif
+
+/* Node initializer. */
+#define        rbp_node_new(a_type, a_field, a_tree, a_node) do {              \
+    rbp_left_set(a_type, a_field, (a_node), &(a_tree)->rbt_nil);       \
+    rbp_right_set(a_type, a_field, (a_node), &(a_tree)->rbt_nil);      \
+    rbp_red_set(a_type, a_field, (a_node));                            \
+} while (0)
+
+/* Tree initializer. */
+#define        rb_new(a_type, a_field, a_tree) do {                            \
+    (a_tree)->rbt_root = &(a_tree)->rbt_nil;                           \
+    rbp_node_new(a_type, a_field, a_tree, &(a_tree)->rbt_nil);         \
+    rbp_black_set(a_type, a_field, &(a_tree)->rbt_nil);                        \
+} while (0)
+
+/* Tree operations. */
+#define        rbp_black_height(a_type, a_field, a_tree, r_height) do {        \
+    a_type *rbp_bh_t;                                                  \
+    for (rbp_bh_t = (a_tree)->rbt_root, (r_height) = 0;                        \
+               rbp_bh_t != &(a_tree)->rbt_nil;                                 \
+               rbp_bh_t = rbp_left_get(a_type, a_field, rbp_bh_t)) {           \
+                       if (rbp_red_get(a_type, a_field, rbp_bh_t) == false) {          \
+                               (r_height)++;                                           \
+                       }                                                               \
+       }                                                                       \
+} while (0)
+
+#define        rbp_first(a_type, a_field, a_tree, a_root, r_node) do {         \
+    for ((r_node) = (a_root);                                          \
+               rbp_left_get(a_type, a_field, (r_node)) != &(a_tree)->rbt_nil;  \
+      (r_node) = rbp_left_get(a_type, a_field, (r_node))) {            \
+    }                                                                  \
+} while (0)
+
+#define        rbp_last(a_type, a_field, a_tree, a_root, r_node) do {          \
+    for ((r_node) = (a_root);                                          \
+               rbp_right_get(a_type, a_field, (r_node)) != &(a_tree)->rbt_nil; \
+               (r_node) = rbp_right_get(a_type, a_field, (r_node))) {          \
+    }                                                                  \
+} while (0)
+
+#define        rbp_next(a_type, a_field, a_cmp, a_tree, a_node, r_node) do {   \
+    if (rbp_right_get(a_type, a_field, (a_node)) != &(a_tree)->rbt_nil) {                                              \
+               rbp_first(a_type, a_field, a_tree, rbp_right_get(a_type,        \
+                                       a_field, (a_node)), (r_node));                          \
+    } else {                                                           \
+               a_type *rbp_n_t = (a_tree)->rbt_root;                           \
+               assert(rbp_n_t != &(a_tree)->rbt_nil);                          \
+               (r_node) = &(a_tree)->rbt_nil;                                  \
+               while (true) {                                                  \
+                       int rbp_n_cmp = (a_cmp)((a_node), rbp_n_t);                     \
+                       if (rbp_n_cmp < 0) {                                    \
+                               (r_node) = rbp_n_t;                                     \
+                               rbp_n_t = rbp_left_get(a_type, a_field, rbp_n_t);       \
+                       } else if (rbp_n_cmp > 0) {                                     \
+                               rbp_n_t = rbp_right_get(a_type, a_field, rbp_n_t);      \
+                       } else {                                                        \
+                               break;                                                  \
+                       }                                                               \
+                       assert(rbp_n_t != &(a_tree)->rbt_nil);                  \
+               }                                                               \
+    }                                                                  \
+} while (0)
+
+#define        rbp_prev(a_type, a_field, a_cmp, a_tree, a_node, r_node) do {   \
+    if (rbp_left_get(a_type, a_field, (a_node)) != &(a_tree)->rbt_nil) {\
+               rbp_last(a_type, a_field, a_tree, rbp_left_get(a_type,          \
+                               a_field, (a_node)), (r_node));                          \
+    } else {                                                           \
+               a_type *rbp_p_t = (a_tree)->rbt_root;                           \
+               assert(rbp_p_t != &(a_tree)->rbt_nil);                          \
+               (r_node) = &(a_tree)->rbt_nil;                                  \
+               while (true) {                                                  \
+                       int rbp_p_cmp = (a_cmp)((a_node), rbp_p_t);                     \
+                       if (rbp_p_cmp < 0) {                                    \
+                               rbp_p_t = rbp_left_get(a_type, a_field, rbp_p_t);       \
+                       } else if (rbp_p_cmp > 0) {                                     \
+                               (r_node) = rbp_p_t;                                     \
+                               rbp_p_t = rbp_right_get(a_type, a_field, rbp_p_t);      \
+                       } else {                                                        \
+                               break;                                                  \
+                       }                                                               \
+                       assert(rbp_p_t != &(a_tree)->rbt_nil);                  \
+               }                                                               \
+    }                                                                  \
+} while (0)
+
+#define        rb_first(a_type, a_field, a_tree, r_node) do {                  \
+    rbp_first(a_type, a_field, a_tree, (a_tree)->rbt_root, (r_node));  \
+    if ((r_node) == &(a_tree)->rbt_nil) {                              \
+               (r_node) = NULL;                                                \
+    }                                                                  \
+} while (0)
+
+#define        rb_last(a_type, a_field, a_tree, r_node) do {                   \
+    rbp_last(a_type, a_field, a_tree, (a_tree)->rbt_root, r_node);     \
+    if ((r_node) == &(a_tree)->rbt_nil) {                              \
+               (r_node) = NULL;                                                \
+    }                                                                  \
+} while (0)
+
+#define        rb_next(a_type, a_field, a_cmp, a_tree, a_node, r_node) do {    \
+    rbp_next(a_type, a_field, a_cmp, a_tree, (a_node), (r_node));      \
+    if ((r_node) == &(a_tree)->rbt_nil) {                              \
+               (r_node) = NULL;                                                \
+    }                                                                  \
+} while (0)
+
+#define        rb_prev(a_type, a_field, a_cmp, a_tree, a_node, r_node) do {    \
+    rbp_prev(a_type, a_field, a_cmp, a_tree, (a_node), (r_node));      \
+    if ((r_node) == &(a_tree)->rbt_nil) {                              \
+               (r_node) = NULL;                                                \
+    }                                                                  \
+} while (0)
+
+#define        rb_search(a_type, a_field, a_cmp, a_tree, a_key, r_node) do {   \
+    int rbp_se_cmp;                                                    \
+    (r_node) = (a_tree)->rbt_root;                                     \
+    while ((r_node) != &(a_tree)->rbt_nil && (rbp_se_cmp = (a_cmp)((a_key), (r_node))) != 0) {         \
+               if (rbp_se_cmp < 0) {                                           \
+                       (r_node) = rbp_left_get(a_type, a_field, (r_node));             \
+               } else {                                                        \
+                       (r_node) = rbp_right_get(a_type, a_field, (r_node));    \
+               }                                                               \
+    }                                                                  \
+    if ((r_node) == &(a_tree)->rbt_nil) {                              \
+               (r_node) = NULL;                                                \
+    }                                                                  \
+} while (0)
+
+/*
+ * Find a match if it exists.  Otherwise, find the next greater node, if one
+ * exists.
+ */
+#define        rb_nsearch(a_type, a_field, a_cmp, a_tree, a_key, r_node) do {  \
+    a_type *rbp_ns_t = (a_tree)->rbt_root;                             \
+    (r_node) = NULL;                                                   \
+    while (rbp_ns_t != &(a_tree)->rbt_nil) {                           \
+               int rbp_ns_cmp = (a_cmp)((a_key), rbp_ns_t);                    \
+               if (rbp_ns_cmp < 0) {                                           \
+                       (r_node) = rbp_ns_t;                                    \
+                       rbp_ns_t = rbp_left_get(a_type, a_field, rbp_ns_t);             \
+               } else if (rbp_ns_cmp > 0) {                                    \
+                       rbp_ns_t = rbp_right_get(a_type, a_field, rbp_ns_t);    \
+               } else {                                                        \
+                       (r_node) = rbp_ns_t;                                    \
+                       break;                                                  \
+               }                                                               \
+    }                                                                  \
+} while (0)
+
+/*
+ * Find a match if it exists.  Otherwise, find the previous lesser node, if one
+ * exists.
+ */
+#define        rb_psearch(a_type, a_field, a_cmp, a_tree, a_key, r_node) do {  \
+    a_type *rbp_ps_t = (a_tree)->rbt_root;                             \
+    (r_node) = NULL;                                                   \
+    while (rbp_ps_t != &(a_tree)->rbt_nil) {                           \
+               int rbp_ps_cmp = (a_cmp)((a_key), rbp_ps_t);                    \
+               if (rbp_ps_cmp < 0) {                                           \
+                       rbp_ps_t = rbp_left_get(a_type, a_field, rbp_ps_t);             \
+               } else if (rbp_ps_cmp > 0) {                                    \
+                       (r_node) = rbp_ps_t;                                    \
+                       rbp_ps_t = rbp_right_get(a_type, a_field, rbp_ps_t);    \
+               } else {                                                        \
+                       (r_node) = rbp_ps_t;                                    \
+                       break;                                                  \
+               }                                                               \
+    }                                                                  \
+} while (0)
+
+#define        rbp_rotate_left(a_type, a_field, a_node, r_node) do {           \
+    (r_node) = rbp_right_get(a_type, a_field, (a_node));               \
+    rbp_right_set(a_type, a_field, (a_node), rbp_left_get(a_type, a_field, (r_node))); \
+    rbp_left_set(a_type, a_field, (r_node), (a_node));                 \
+} while (0)
+
+#define        rbp_rotate_right(a_type, a_field, a_node, r_node) do {          \
+    (r_node) = rbp_left_get(a_type, a_field, (a_node));                        \
+    rbp_left_set(a_type, a_field, (a_node),    rbp_right_get(a_type, a_field, (r_node)));      \
+    rbp_right_set(a_type, a_field, (r_node), (a_node));                        \
+} while (0)
+
+#define        rbp_lean_left(a_type, a_field, a_node, r_node) do {             \
+    bool rbp_ll_red;                                                   \
+    rbp_rotate_left(a_type, a_field, (a_node), (r_node));              \
+    rbp_ll_red = rbp_red_get(a_type, a_field, (a_node));               \
+    rbp_color_set(a_type, a_field, (r_node), rbp_ll_red);              \
+    rbp_red_set(a_type, a_field, (a_node));                            \
+} while (0)
+
+#define        rbp_lean_right(a_type, a_field, a_node, r_node) do {            \
+    bool rbp_lr_red;                                                   \
+    rbp_rotate_right(a_type, a_field, (a_node), (r_node));             \
+    rbp_lr_red = rbp_red_get(a_type, a_field, (a_node));               \
+    rbp_color_set(a_type, a_field, (r_node), rbp_lr_red);              \
+    rbp_red_set(a_type, a_field, (a_node));                            \
+} while (0)
+
+#define        rbp_move_red_left(a_type, a_field, a_node, r_node) do {         \
+    a_type *rbp_mrl_t, *rbp_mrl_u;                                     \
+    rbp_mrl_t = rbp_left_get(a_type, a_field, (a_node));               \
+    rbp_red_set(a_type, a_field, rbp_mrl_t);                           \
+    rbp_mrl_t = rbp_right_get(a_type, a_field, (a_node));              \
+    rbp_mrl_u = rbp_left_get(a_type, a_field, rbp_mrl_t);              \
+    if (rbp_red_get(a_type, a_field, rbp_mrl_u)) {                     \
+               rbp_rotate_right(a_type, a_field, rbp_mrl_t, rbp_mrl_u);        \
+               rbp_right_set(a_type, a_field, (a_node), rbp_mrl_u);            \
+               rbp_rotate_left(a_type, a_field, (a_node), (r_node));           \
+               rbp_mrl_t = rbp_right_get(a_type, a_field, (a_node));           \
+               if (rbp_red_get(a_type, a_field, rbp_mrl_t)) {                  \
+                       rbp_black_set(a_type, a_field, rbp_mrl_t);                      \
+                       rbp_red_set(a_type, a_field, (a_node));                 \
+                       rbp_rotate_left(a_type, a_field, (a_node), rbp_mrl_t);  \
+                       rbp_left_set(a_type, a_field, (r_node), rbp_mrl_t);             \
+               } else {                                                        \
+                       rbp_black_set(a_type, a_field, (a_node));                       \
+               }                                                               \
+    } else {                                                           \
+               rbp_red_set(a_type, a_field, (a_node));                         \
+               rbp_rotate_left(a_type, a_field, (a_node), (r_node));           \
+    }                                                                  \
+} while (0)
+
+#define        rbp_move_red_right(a_type, a_field, a_node, r_node) do {        \
+    a_type *rbp_mrr_t;                                                 \
+    rbp_mrr_t = rbp_left_get(a_type, a_field, (a_node));               \
+    if (rbp_red_get(a_type, a_field, rbp_mrr_t)) {                     \
+               a_type *rbp_mrr_u, *rbp_mrr_v;                                  \
+               rbp_mrr_u = rbp_right_get(a_type, a_field, rbp_mrr_t);          \
+               rbp_mrr_v = rbp_left_get(a_type, a_field, rbp_mrr_u);           \
+               if (rbp_red_get(a_type, a_field, rbp_mrr_v)) {                  \
+                       rbp_color_set(a_type, a_field, rbp_mrr_u, rbp_red_get(a_type, a_field, (a_node))); \
+                       rbp_black_set(a_type, a_field, rbp_mrr_v);                      \
+                       rbp_rotate_left(a_type, a_field, rbp_mrr_t, rbp_mrr_u); \
+                       rbp_left_set(a_type, a_field, (a_node), rbp_mrr_u);             \
+                       rbp_rotate_right(a_type, a_field, (a_node), (r_node));  \
+                       rbp_rotate_left(a_type, a_field, (a_node), rbp_mrr_t);  \
+                       rbp_right_set(a_type, a_field, (r_node), rbp_mrr_t);    \
+               } else {                                                        \
+                       rbp_color_set(a_type, a_field, rbp_mrr_t, rbp_red_get(a_type, a_field, (a_node))); \
+                       rbp_red_set(a_type, a_field, rbp_mrr_u);                        \
+                       rbp_rotate_right(a_type, a_field, (a_node), (r_node));  \
+                       rbp_rotate_left(a_type, a_field, (a_node), rbp_mrr_t);  \
+                       rbp_right_set(a_type, a_field, (r_node), rbp_mrr_t);    \
+               }                                                               \
+               rbp_red_set(a_type, a_field, (a_node));                         \
+    } else {                                                           \
+               rbp_red_set(a_type, a_field, rbp_mrr_t);                        \
+               rbp_mrr_t = rbp_left_get(a_type, a_field, rbp_mrr_t);           \
+               if (rbp_red_get(a_type, a_field, rbp_mrr_t)) {                  \
+                       rbp_black_set(a_type, a_field, rbp_mrr_t);                      \
+                       rbp_rotate_right(a_type, a_field, (a_node), (r_node));  \
+                       rbp_rotate_left(a_type, a_field, (a_node), rbp_mrr_t);  \
+                       rbp_right_set(a_type, a_field, (r_node), rbp_mrr_t);    \
+               } else {                                                        \
+                       rbp_rotate_left(a_type, a_field, (a_node), (r_node));   \
+               }                                                               \
+    }                                                                  \
+} while (0)
+
+#define        rb_insert(a_type, a_field, a_cmp, a_tree, a_node) do {          \
+    a_type rbp_i_s;                                                    \
+    a_type *rbp_i_g, *rbp_i_p, *rbp_i_c, *rbp_i_t, *rbp_i_u;           \
+    int rbp_i_cmp = 0;                                                 \
+    rbp_i_g = &(a_tree)->rbt_nil;                                      \
+    rbp_left_set(a_type, a_field, &rbp_i_s, (a_tree)->rbt_root);       \
+    rbp_right_set(a_type, a_field, &rbp_i_s, &(a_tree)->rbt_nil);      \
+    rbp_black_set(a_type, a_field, &rbp_i_s);                          \
+    rbp_i_p = &rbp_i_s;                                                        \
+    rbp_i_c = (a_tree)->rbt_root;                                      \
+    /* Iteratively search down the tree for the insertion point,      */\
+    /* splitting 4-nodes as they are encountered.  At the end of each */\
+    /* iteration, rbp_i_g->rbp_i_p->rbp_i_c is a 3-level path down    */\
+    /* the tree, assuming a sufficiently deep tree.                   */\
+    while (rbp_i_c != &(a_tree)->rbt_nil) {                            \
+               rbp_i_t = rbp_left_get(a_type, a_field, rbp_i_c);               \
+               rbp_i_u = rbp_left_get(a_type, a_field, rbp_i_t);               \
+               if (rbp_red_get(a_type, a_field, rbp_i_t)                       \
+                       && rbp_red_get(a_type, a_field, rbp_i_u)) {                     \
+                       /* rbp_i_c is the top of a logical 4-node, so split it.   */\
+                       /* This iteration does not move down the tree, due to the */\
+                       /* disruptiveness of node splitting.                      */\
+                       /*                                                        */\
+                       /* Rotate right.                                          */\
+                       rbp_rotate_right(a_type, a_field, rbp_i_c, rbp_i_t);    \
+                       /* Pass red links up one level.                           */\
+                       rbp_i_u = rbp_left_get(a_type, a_field, rbp_i_t);               \
+                       rbp_black_set(a_type, a_field, rbp_i_u);                        \
+                       if (rbp_left_get(a_type, a_field, rbp_i_p) == rbp_i_c) {        \
+                               rbp_left_set(a_type, a_field, rbp_i_p, rbp_i_t);        \
+                               rbp_i_c = rbp_i_t;                                      \
+                       } else {                                                        \
+                               /* rbp_i_c was the right child of rbp_i_p, so rotate  */\
+                               /* left in order to maintain the left-leaning         */\
+                               /* invariant.                                         */\
+                               assert(rbp_right_get(a_type, a_field, rbp_i_p) == rbp_i_c);     \
+                               rbp_right_set(a_type, a_field, rbp_i_p, rbp_i_t);       \
+                               rbp_lean_left(a_type, a_field, rbp_i_p, rbp_i_u);       \
+                               if (rbp_left_get(a_type, a_field, rbp_i_g) == rbp_i_p) {\
+                                       rbp_left_set(a_type, a_field, rbp_i_g, rbp_i_u);        \
+                               } else {                                                \
+                                       assert(rbp_right_get(a_type, a_field, rbp_i_g) == rbp_i_p);     \
+                                       rbp_right_set(a_type, a_field, rbp_i_g, rbp_i_u);       \
+                               }                                                       \
+                               rbp_i_p = rbp_i_u;                                      \
+                               rbp_i_cmp = (a_cmp)((a_node), rbp_i_p);                 \
+                               if (rbp_i_cmp < 0) {                                    \
+                                       rbp_i_c = rbp_left_get(a_type, a_field, rbp_i_p);       \
+                               } else {                                                \
+                                       assert(rbp_i_cmp > 0);                          \
+                                       rbp_i_c = rbp_right_get(a_type, a_field, rbp_i_p);      \
+                               }                                                       \
+                               continue;                                               \
+                       }                                                               \
+               }                                                               \
+               rbp_i_g = rbp_i_p;                                              \
+               rbp_i_p = rbp_i_c;                                              \
+               rbp_i_cmp = (a_cmp)((a_node), rbp_i_c);                         \
+               if (rbp_i_cmp < 0) {                                            \
+                       rbp_i_c = rbp_left_get(a_type, a_field, rbp_i_c);               \
+               } else {                                                        \
+                       assert(rbp_i_cmp > 0);                                  \
+                       rbp_i_c = rbp_right_get(a_type, a_field, rbp_i_c);              \
+               }                                                               \
+    }                                                                  \
+    /* rbp_i_p now refers to the node under which to insert.          */\
+    rbp_node_new(a_type, a_field, a_tree, (a_node));                   \
+    if (rbp_i_cmp > 0) {                                               \
+               rbp_right_set(a_type, a_field, rbp_i_p, (a_node));              \
+               rbp_lean_left(a_type, a_field, rbp_i_p, rbp_i_t);               \
+               if (rbp_left_get(a_type, a_field, rbp_i_g) == rbp_i_p) {        \
+                       rbp_left_set(a_type, a_field, rbp_i_g, rbp_i_t);                \
+               } else if (rbp_right_get(a_type, a_field, rbp_i_g) == rbp_i_p) {\
+                       rbp_right_set(a_type, a_field, rbp_i_g, rbp_i_t);               \
+               }                                                               \
+    } else {                                                           \
+               rbp_left_set(a_type, a_field, rbp_i_p, (a_node));               \
+    }                                                                  \
+    /* Update the root and make sure that it is black.                */\
+    (a_tree)->rbt_root = rbp_left_get(a_type, a_field, &rbp_i_s);      \
+    rbp_black_set(a_type, a_field, (a_tree)->rbt_root);                        \
+} while (0)
+
+#define        rb_remove(a_type, a_field, a_cmp, a_tree, a_node) do {          \
+    a_type rbp_r_s;                                                    \
+    a_type *rbp_r_p, *rbp_r_c, *rbp_r_xp, *rbp_r_t, *rbp_r_u;          \
+    int rbp_r_cmp;                                                     \
+    rbp_left_set(a_type, a_field, &rbp_r_s, (a_tree)->rbt_root);       \
+    rbp_right_set(a_type, a_field, &rbp_r_s, &(a_tree)->rbt_nil);      \
+    rbp_black_set(a_type, a_field, &rbp_r_s);                          \
+    rbp_r_p = &rbp_r_s;                                                        \
+    rbp_r_c = (a_tree)->rbt_root;                                      \
+    rbp_r_xp = &(a_tree)->rbt_nil;                                     \
+    /* Iterate down the tree, but always transform 2-nodes to 3- or   */\
+    /* 4-nodes in order to maintain the invariant that the current    */\
+    /* node is not a 2-node.  This allows simple deletion once a leaf */\
+    /* is reached.  Handle the root specially though, since there may */\
+    /* be no way to convert it from a 2-node to a 3-node.             */\
+    rbp_r_cmp = (a_cmp)((a_node), rbp_r_c);                            \
+    if (rbp_r_cmp < 0) {                                               \
+               rbp_r_t = rbp_left_get(a_type, a_field, rbp_r_c);               \
+               rbp_r_u = rbp_left_get(a_type, a_field, rbp_r_t);               \
+               if (rbp_red_get(a_type, a_field, rbp_r_t) == false              \
+                       && rbp_red_get(a_type, a_field, rbp_r_u) == false) {            \
+                       /* Apply standard transform to prepare for left move.     */\
+                       rbp_move_red_left(a_type, a_field, rbp_r_c, rbp_r_t);   \
+                       rbp_black_set(a_type, a_field, rbp_r_t);                        \
+                       rbp_left_set(a_type, a_field, rbp_r_p, rbp_r_t);                \
+                       rbp_r_c = rbp_r_t;                                              \
+               } else {                                                        \
+                       /* Move left.                                             */\
+                       rbp_r_p = rbp_r_c;                                              \
+                       rbp_r_c = rbp_left_get(a_type, a_field, rbp_r_c);               \
+               }                                                               \
+    } else {                                                           \
+               if (rbp_r_cmp == 0) {                                           \
+                       assert((a_node) == rbp_r_c);                            \
+                       if (rbp_right_get(a_type, a_field, rbp_r_c)     == &(a_tree)->rbt_nil) { \
+                               /* Delete root node (which is also a leaf node).      */\
+                               if (rbp_left_get(a_type, a_field, rbp_r_c) != &(a_tree)->rbt_nil) {     \
+                                       rbp_lean_right(a_type, a_field, rbp_r_c, rbp_r_t);      \
+                                       rbp_right_set(a_type, a_field, rbp_r_t, &(a_tree)->rbt_nil);    \
+                               } else {                                                \
+                                       rbp_r_t = &(a_tree)->rbt_nil;                   \
+                               }                                                       \
+                               rbp_left_set(a_type, a_field, rbp_r_p, rbp_r_t);        \
+                       } else {                                                        \
+                               /* This is the node we want to delete, but we will    */\
+                               /* instead swap it with its successor and delete the  */\
+                               /* successor.  Record enough information to do the    */\
+                               /* swap later.  rbp_r_xp is the a_node's parent.      */\
+                               rbp_r_xp = rbp_r_p;                                     \
+                               rbp_r_cmp = 1; /* Note that deletion is incomplete.   */\
+                       }                                                               \
+               }                                                               \
+               if (rbp_r_cmp == 1) {                                           \
+                       if (rbp_red_get(a_type, a_field, rbp_left_get(a_type,   \
+                                       a_field, rbp_right_get(a_type, a_field, rbp_r_c))) == false) { \
+                               rbp_r_t = rbp_left_get(a_type, a_field, rbp_r_c);       \
+                               if (rbp_red_get(a_type, a_field, rbp_r_t)) {            \
+                                       /* Standard transform.                            */\
+                                       rbp_move_red_right(a_type, a_field, rbp_r_c, rbp_r_t);  \
+                               } else {                                                \
+                                       /* Root-specific transform.                       */\
+                                       rbp_red_set(a_type, a_field, rbp_r_c);          \
+                                       rbp_r_u = rbp_left_get(a_type, a_field, rbp_r_t);       \
+                                       if (rbp_red_get(a_type, a_field, rbp_r_u)) {    \
+                                               rbp_black_set(a_type, a_field, rbp_r_u);        \
+                                               rbp_rotate_right(a_type, a_field, rbp_r_c, rbp_r_t);    \
+                                               rbp_rotate_left(a_type, a_field, rbp_r_c, rbp_r_u);             \
+                                               rbp_right_set(a_type, a_field, rbp_r_t, rbp_r_u);               \
+                                       } else {                                                \
+                                               rbp_red_set(a_type, a_field, rbp_r_t);          \
+                                               rbp_rotate_left(a_type, a_field, rbp_r_c, rbp_r_t);             \
+                                       }                                                       \
+                               }                                                       \
+                               rbp_left_set(a_type, a_field, rbp_r_p, rbp_r_t);        \
+                               rbp_r_c = rbp_r_t;                                      \
+                       } else {                                                        \
+                               /* Move right                                     */\
+                               rbp_r_p = rbp_r_c;                                      \
+                               rbp_r_c = rbp_right_get(a_type, a_field, rbp_r_c);      \
+                       }                                                               \
+               }                                                               \
+    }                                                                  \
+    if (rbp_r_cmp != 0) {                                              \
+               while (true) {                                                  \
+                       assert(rbp_r_p != &(a_tree)->rbt_nil);                  \
+                       rbp_r_cmp = (a_cmp)((a_node), rbp_r_c);                 \
+                       if (rbp_r_cmp < 0) {                                    \
+                               rbp_r_t = rbp_left_get(a_type, a_field, rbp_r_c);       \
+                               if (rbp_r_t == &(a_tree)->rbt_nil) {                    \
+                                       /* rbp_r_c now refers to the successor node to    */\
+                                       /* relocate, and rbp_r_xp/a_node refer to the     */\
+                                       /* context for the relocation.                    */\
+                                       if (rbp_left_get(a_type, a_field, rbp_r_xp)     == (a_node)) {                  \
+                                               rbp_left_set(a_type, a_field, rbp_r_xp, rbp_r_c);                               \
+                                       } else {                                                \
+                                               assert(rbp_right_get(a_type, a_field, rbp_r_xp) == (a_node));   \
+                                               rbp_right_set(a_type, a_field, rbp_r_xp, rbp_r_c);                              \
+                                       }                                                       \
+                                       rbp_left_set(a_type, a_field, rbp_r_c, rbp_left_get(a_type, a_field, (a_node)));        \
+                                       rbp_right_set(a_type, a_field, rbp_r_c, rbp_right_get(a_type, a_field, (a_node)));      \
+                                       rbp_color_set(a_type, a_field, rbp_r_c, rbp_red_get(a_type, a_field, (a_node)));        \
+                                       if (rbp_left_get(a_type, a_field, rbp_r_p) == rbp_r_c) {                                        \
+                                               rbp_left_set(a_type, a_field, rbp_r_p, &(a_tree)->rbt_nil);                             \
+                                       } else {                                                \
+                                               assert(rbp_right_get(a_type, a_field, rbp_r_p) == rbp_r_c);                             \
+                                               rbp_right_set(a_type, a_field, rbp_r_p, &(a_tree)->rbt_nil);                    \
+                                       }                                                       \
+                                       break;                                          \
+                               }                                                       \
+                               rbp_r_u = rbp_left_get(a_type, a_field, rbp_r_t);       \
+                               if (rbp_red_get(a_type, a_field, rbp_r_t) == false \
+                                               && rbp_red_get(a_type, a_field, rbp_r_u) == false) {    \
+                                               rbp_move_red_left(a_type, a_field, rbp_r_c, rbp_r_t);   \
+                                       if (rbp_left_get(a_type, a_field, rbp_r_p) == rbp_r_c) {        \
+                                               rbp_left_set(a_type, a_field, rbp_r_p, rbp_r_t);\
+                                       } else {                                                \
+                                               rbp_right_set(a_type, a_field, rbp_r_p, rbp_r_t);               \
+                                       }                                                       \
+                                       rbp_r_c = rbp_r_t;                                      \
+                               } else {                                                \
+                                       rbp_r_p = rbp_r_c;                                      \
+                                       rbp_r_c = rbp_left_get(a_type, a_field, rbp_r_c);       \
+                               }                                                       \
+                       } else {                                                        \
+                               /* Check whether to delete this node (it has to be    */\
+                               /* the correct node and a leaf node).                 */\
+                               if (rbp_r_cmp == 0) {                                   \
+                                       assert((a_node) == rbp_r_c);                    \
+                                       if (rbp_right_get(a_type, a_field, rbp_r_c) == &(a_tree)->rbt_nil) {    \
+                                               /* Delete leaf node.                          */\
+                                               if (rbp_left_get(a_type, a_field, rbp_r_c) != &(a_tree)->rbt_nil) {     \
+                                                       rbp_lean_right(a_type, a_field, rbp_r_c, rbp_r_t);      \
+                                                       rbp_right_set(a_type, a_field, rbp_r_t, &(a_tree)->rbt_nil);    \
+                                               } else {                                        \
+                                                       rbp_r_t = &(a_tree)->rbt_nil;           \
+                                               }                                               \
+                                               if (rbp_left_get(a_type, a_field, rbp_r_p) == rbp_r_c) {                \
+                                                       rbp_left_set(a_type, a_field, rbp_r_p, rbp_r_t);                        \
+                                               } else {                                        \
+                                                       rbp_right_set(a_type, a_field, rbp_r_p, rbp_r_t);                       \
+                                               }                                               \
+                                               break;                                          \
+                                       } else {                                                \
+                                               /* This is the node we want to delete, but we */\
+                                               /* will instead swap it with its successor    */\
+                                               /* and delete the successor.  Record enough   */\
+                                               /* information to do the swap later.          */\
+                                               /* rbp_r_xp is a_node's parent.               */\
+                                               rbp_r_xp = rbp_r_p;                             \
+                                       }                                                       \
+                               }                                                       \
+                               rbp_r_t = rbp_right_get(a_type, a_field, rbp_r_c);      \
+                               rbp_r_u = rbp_left_get(a_type, a_field, rbp_r_t);       \
+                               if (rbp_red_get(a_type, a_field, rbp_r_u) == false) {   \
+                                       rbp_move_red_right(a_type, a_field, rbp_r_c,    \
+                                       rbp_r_t);                                               \
+                                       if (rbp_left_get(a_type, a_field, rbp_r_p) == rbp_r_c) {                \
+                                               rbp_left_set(a_type, a_field, rbp_r_p, rbp_r_t);\
+                                       } else {                                                \
+                                               rbp_right_set(a_type, a_field, rbp_r_p, rbp_r_t); \
+                                       }                                                       \
+                                       rbp_r_c = rbp_r_t;                                      \
+                               } else {                                                \
+                                       rbp_r_p = rbp_r_c;                                      \
+                                       rbp_r_c = rbp_right_get(a_type, a_field, rbp_r_c);      \
+                               }                                                       \
+                       }                                                               \
+               }                                                               \
+    }                                                                  \
+    /* Update root.                                                   */\
+    (a_tree)->rbt_root = rbp_left_get(a_type, a_field, &rbp_r_s);      \
+} while (0)
+
+/*
+ * The rb_wrap() macro provides a convenient way to wrap functions around the
+ * cpp macros.  The main benefits of wrapping are that 1) repeated macro
+ * expansion can cause code bloat, especially for rb_{insert,remove)(), and
+ * 2) type, linkage, comparison functions, etc. need not be specified at every
+ * call point.
+ */
+
+#define        rb_wrap(a_attr, a_prefix, a_tree_type, a_type, a_field, a_cmp)  \
+a_attr void                                                            \
+a_prefix##new(a_tree_type *tree) {                                     \
+    rb_new(a_type, a_field, tree);                                     \
+}                                                                      \
+a_attr a_type *                                                                \
+a_prefix##first(a_tree_type *tree) {                                   \
+    a_type *ret;                                                       \
+    rb_first(a_type, a_field, tree, ret);                              \
+    return (ret);                                                      \
+}                                                                      \
+a_attr a_type *                                                                \
+a_prefix##last(a_tree_type *tree) {                                    \
+    a_type *ret;                                                       \
+    rb_last(a_type, a_field, tree, ret);                               \
+    return (ret);                                                      \
+}                                                                      \
+a_attr a_type *                                                                \
+a_prefix##next(a_tree_type *tree, a_type *node) {                      \
+    a_type *ret;                                                       \
+    rb_next(a_type, a_field, a_cmp, tree, node, ret);                  \
+    return (ret);                                                      \
+}                                                                      \
+a_attr a_type *                                                                \
+a_prefix##prev(a_tree_type *tree, a_type *node) {                      \
+    a_type *ret;                                                       \
+    rb_prev(a_type, a_field, a_cmp, tree, node, ret);                  \
+    return (ret);                                                      \
+}                                                                      \
+a_attr a_type *                                                                \
+a_prefix##search(a_tree_type *tree, a_type *key) {                     \
+    a_type *ret;                                                       \
+    rb_search(a_type, a_field, a_cmp, tree, key, ret);                 \
+    return (ret);                                                      \
+}                                                                      \
+a_attr a_type *                                                                \
+a_prefix##nsearch(a_tree_type *tree, a_type *key) {                    \
+    a_type *ret;                                                       \
+    rb_nsearch(a_type, a_field, a_cmp, tree, key, ret);                        \
+    return (ret);                                                      \
+}                                                                      \
+a_attr a_type *                                                                \
+a_prefix##psearch(a_tree_type *tree, a_type *key) {                    \
+    a_type *ret;                                                       \
+    rb_psearch(a_type, a_field, a_cmp, tree, key, ret);                        \
+    return (ret);                                                      \
+}                                                                      \
+a_attr void                                                            \
+a_prefix##insert(a_tree_type *tree, a_type *node) {                    \
+    rb_insert(a_type, a_field, a_cmp, tree, node);                     \
+}                                                                      \
+a_attr void                                                            \
+a_prefix##remove(a_tree_type *tree, a_type *node) {                    \
+    rb_remove(a_type, a_field, a_cmp, tree, node);                     \
+}
+
+/*
+ * The iterators simulate recursion via an array of pointers that store the
+ * current path.  This is critical to performance, since a series of calls to
+ * rb_{next,prev}() would require time proportional to (n lg n), whereas this
+ * implementation only requires time proportional to (n).
+ *
+ * Since the iterators cache a path down the tree, any tree modification may
+ * cause the cached path to become invalid.  In order to continue iteration,
+ * use something like the following sequence:
+ *
+ *   {
+ *       a_type *node, *tnode;
+ *
+ *       rb_foreach_begin(a_type, a_field, a_tree, node) {
+ *           ...
+ *           rb_next(a_type, a_field, a_cmp, a_tree, node, tnode);
+ *           rb_remove(a_type, a_field, a_cmp, a_tree, node);
+ *           rb_foreach_next(a_type, a_field, a_cmp, a_tree, tnode);
+ *           ...
+ *       } rb_foreach_end(a_type, a_field, a_tree, node)
+ *   }
+ *
+ * Note that this idiom is not advised if every iteration modifies the tree,
+ * since in that case there is no algorithmic complexity improvement over a
+ * series of rb_{next,prev}() calls, thus making the setup overhead wasted
+ * effort.
+ */
+
+#define        rb_foreach_begin(a_type, a_field, a_tree, a_var) { /* brace A */        \
+    /* Compute the maximum possible tree depth (3X the black height). */\
+    unsigned rbp_f_height;                                             \
+    rbp_black_height(a_type, a_field, a_tree, rbp_f_height);           \
+    rbp_f_height *= 3;                                                 \
+    {          /* brace B */                                                   \
+               /* Initialize the path to contain the left spine.             */\
+               a_type *rbp_f_path[rbp_f_height];                               \
+               a_type *rbp_f_node;                                             \
+               bool rbp_f_synced = false;                                      \
+               unsigned rbp_f_depth = 0;                                       \
+               if ((a_tree)->rbt_root != &(a_tree)->rbt_nil) {                 \
+                       rbp_f_path[rbp_f_depth] = (a_tree)->rbt_root;           \
+                       rbp_f_depth++;                                          \
+                       while ((rbp_f_node = rbp_left_get(a_type, a_field,              \
+                                       rbp_f_path[rbp_f_depth-1])) != &(a_tree)->rbt_nil) {    \
+                               rbp_f_path[rbp_f_depth] = rbp_f_node;                   \
+                               rbp_f_depth++;                                          \
+                       }                                                               \
+               }                                                               \
+               /* While the path is non-empty, iterate.                      */\
+               while (rbp_f_depth > 0) {               /* brace C */                   \
+                       (a_var) = rbp_f_path[rbp_f_depth-1];    
+
+/* 
+ * Note that rb_foreach_begin omits closing }'s because
+ * it expects that it will be succeeded by a call to 
+ * rb_foreach_end which will have the closing }
+ */
+
+/* Only use if modifying the tree during iteration. */
+#define        rb_foreach_next(a_type, a_field, a_cmp, a_tree, a_node)         \
+           /* Re-initialize the path to contain the path to a_node.  */\
+           rbp_f_depth = 0;                                            \
+           if (a_node != NULL) {                                       \
+                       if ((a_tree)->rbt_root != &(a_tree)->rbt_nil) {         \
+                               rbp_f_path[rbp_f_depth] = (a_tree)->rbt_root;   \
+                               rbp_f_depth++;                                  \
+                               rbp_f_node = rbp_f_path[0];                             \
+                               while (true) {                                  \
+                                       int rbp_f_cmp = (a_cmp)((a_node),               \
+                                       rbp_f_path[rbp_f_depth-1]);                     \
+                                       if (rbp_f_cmp < 0) {                            \
+                                               rbp_f_node = rbp_left_get(a_type, a_field,      \
+                                               rbp_f_path[rbp_f_depth-1]);             \
+                                       } else if (rbp_f_cmp > 0) {                     \
+                                               rbp_f_node = rbp_right_get(a_type, a_field,     \
+                                                               rbp_f_path[rbp_f_depth-1]);             \
+                                       } else {                                        \
+                                               break;                                  \
+                                       }                                               \
+                                       assert(rbp_f_node != &(a_tree)->rbt_nil);       \
+                                       rbp_f_path[rbp_f_depth] = rbp_f_node;           \
+                                       rbp_f_depth++;                                  \
+                               }                                                       \
+                       }                                                       \
+           }                                                           \
+           rbp_f_synced = true;
+
+#define        rb_foreach_end(a_type, a_field, a_tree, a_var)                  \
+                       if (rbp_f_synced) {                                             \
+                               rbp_f_synced = false;                                   \
+                               continue;                                               \
+                       }                                                               \
+                       /* Find the successor.                                    */\
+                       if ((rbp_f_node = rbp_right_get(a_type, a_field,                \
+                                       rbp_f_path[rbp_f_depth-1])) != &(a_tree)->rbt_nil) {    \
+                               /* The successor is the left-most node in the right   */\
+                               /* subtree.                                           */\
+                               rbp_f_path[rbp_f_depth] = rbp_f_node;                   \
+                               rbp_f_depth++;                                          \
+                               while ((rbp_f_node = rbp_left_get(a_type, a_field,      \
+                                               rbp_f_path[rbp_f_depth-1])) != &(a_tree)->rbt_nil) {    \
+                                       rbp_f_path[rbp_f_depth] = rbp_f_node;           \
+                                       rbp_f_depth++;                                  \
+                               }                                                       \
+                       } else {                                                        \
+                               /* The successor is above the current node.  Unwind   */\
+                               /* until a left-leaning edge is removed from the      */\
+                               /* path, or the path is empty.                        */\
+                               for (rbp_f_depth--; rbp_f_depth > 0; rbp_f_depth--) {   \
+                                       if (rbp_left_get(a_type, a_field, rbp_f_path[rbp_f_depth-1]) \
+                                                       == rbp_f_path[rbp_f_depth]) {                   \
+                                               break;                                          \
+                                       }                                                       \
+                               }                                                       \
+                       }                                                               \
+               }       /* close brace C */                                                     \
+    }  /* close brace B */                                                     \
+} /* close brace A */
+
+
+
+#define        rb_foreach_reverse_begin(a_type, a_field, a_tree, a_var) {  /* brace A */ \
+    /* Compute the maximum possible tree depth (3X the black height). */\
+    unsigned rbp_fr_height;                                            \
+    rbp_black_height(a_type, a_field, a_tree, rbp_fr_height);          \
+    rbp_fr_height *= 3;                                                        \
+    {  /* brace B */                                                           \
+               /* Initialize the path to contain the right spine.            */\
+               a_type *rbp_fr_path[rbp_fr_height];                             \
+               a_type *rbp_fr_node;                                            \
+               bool rbp_fr_synced = false;                                     \
+               unsigned rbp_fr_depth = 0;                                      \
+               if ((a_tree)->rbt_root != &(a_tree)->rbt_nil) {                 \
+                       rbp_fr_path[rbp_fr_depth] = (a_tree)->rbt_root;         \
+                       rbp_fr_depth++;                                         \
+                       while ((rbp_fr_node = rbp_right_get(a_type, a_field,    \
+                                       rbp_fr_path[rbp_fr_depth-1])) != &(a_tree)->rbt_nil) {  \
+                               rbp_fr_path[rbp_fr_depth] = rbp_fr_node;                \
+                               rbp_fr_depth++;                                         \
+                       }                                                               \
+               }                                                               \
+               /* While the path is non-empty, iterate.                      */\
+               while (rbp_fr_depth > 0) {       /* brace C */                  \
+                       (a_var) = rbp_fr_path[rbp_fr_depth-1];
+
+
+/* Only use if modifying the tree during iteration. */
+#define        rb_foreach_reverse_prev(a_type, a_field, a_cmp, a_tree, a_node) \
+           /* Re-initialize the path to contain the path to a_node.  */\
+           rbp_fr_depth = 0;                                           \
+           if (a_node != NULL) {                                       \
+                       if ((a_tree)->rbt_root != &(a_tree)->rbt_nil) {         \
+                               rbp_fr_path[rbp_fr_depth] = (a_tree)->rbt_root; \
+                               rbp_fr_depth++;                                 \
+                               rbp_fr_node = rbp_fr_path[0];                   \
+                               while (true) {                                  \
+                                       int rbp_fr_cmp = (a_cmp)((a_node), rbp_fr_path[rbp_fr_depth-1]);        \
+                                       if (rbp_fr_cmp < 0) {                           \
+                                               rbp_fr_node = rbp_left_get(a_type, a_field,     \
+                                               rbp_fr_path[rbp_fr_depth-1]);           \
+                                       } else if (rbp_fr_cmp > 0) {                    \
+                                               rbp_fr_node = rbp_right_get(a_type, a_field, rbp_fr_path[rbp_fr_depth-1]);      \
+                                       } else {                                        \
+                                               break;                                  \
+                                       }                                               \
+                                       assert(rbp_fr_node != &(a_tree)->rbt_nil);      \
+                                       rbp_fr_path[rbp_fr_depth] = rbp_fr_node;        \
+                                       rbp_fr_depth++;                                 \
+                               }                                                       \
+                       }                                                       \
+               }                                                               \
+               rbp_fr_synced = true;
+
+#define        rb_foreach_reverse_end(a_type, a_field, a_tree, a_var)          \
+                       if (rbp_fr_synced) {                                    \
+                               rbp_fr_synced = false;                                  \
+                               continue;                                               \
+                       }                                                               \
+                       if (rbp_fr_depth == 0) {                                        \
+                               /* rb_foreach_reverse_sync() was called with a NULL   */\
+                               /* a_node.                                            */\
+                               break;                                                  \
+                       }                                                               \
+                       /* Find the predecessor.                                  */\
+                       if ((rbp_fr_node = rbp_left_get(a_type, a_field,                \
+                                       rbp_fr_path[rbp_fr_depth-1])) != &(a_tree)->rbt_nil) {  \
+                               /* The predecessor is the right-most node in the left */\
+                               /* subtree.                                           */\
+                               rbp_fr_path[rbp_fr_depth] = rbp_fr_node;                \
+                               rbp_fr_depth++;                                         \
+                               while ((rbp_fr_node = rbp_right_get(a_type, a_field,    \
+                                               rbp_fr_path[rbp_fr_depth-1])) != &(a_tree)->rbt_nil) {\
+                                       rbp_fr_path[rbp_fr_depth] = rbp_fr_node;                \
+                                       rbp_fr_depth++;                                 \
+                               }                                                       \
+                       } else {                                                        \
+                               /* The predecessor is above the current node.  Unwind */\
+                               /* until a right-leaning edge is removed from the     */\
+                               /* path, or the path is empty.                        */\
+                               for (rbp_fr_depth--; rbp_fr_depth > 0; rbp_fr_depth--) {\
+                                       if (rbp_right_get(a_type, a_field, rbp_fr_path[rbp_fr_depth-1]) \
+                                                       == rbp_fr_path[rbp_fr_depth]) {                 \
+                                               break;                                          \
+                                       }                                                       \
+                               }                                                       \
+                       }                                                               \
+               }       /* Close brace C */                                     \
+    } /* close brace B */                                              \
+} /* close brace A*/
+
+#endif /* RB_H_ */