[libc][tsearch] add tsearch functions #172625
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SchrodingerZhu
commented
Dec 17, 2025
SchrodingerZhu
commented
- [libc][tsearch] scaffold WAVL header
- stage
- stage
- stage the work
- stage the work
- update ref
- update
- update
- update
- update
- add fuzzing
- reduce size for hermetic test
- improve doc
- add tree walk API
- reduce test size further for hermetic tests
- add doc
- separate flag and parent pointer
- stage
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@llvm/pr-subscribers-libc Author: Schrodinger ZHU Yifan (SchrodingerZhu) Changes
Patch is 66.65 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/172625.diff 33 Files Affected:
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index 970c825bbfc96..f2a634ea4afa1 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -1116,6 +1116,12 @@ if(LLVM_LIBC_FULL_BUILD)
libc.src.search.lfind
libc.src.search.lsearch
libc.src.search.remque
+ libc.src.search.tdelete
+ libc.src.search.tdestroy
+ libc.src.search.tfind
+ libc.src.search.tsearch
+ libc.src.search.twalk
+ libc.src.search.twalk_r
# threads.h entrypoints
libc.src.threads.call_once
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 9399b284fa2da..a6ce8a3715d51 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -1298,6 +1298,12 @@ if(LLVM_LIBC_FULL_BUILD)
libc.src.search.lfind
libc.src.search.lsearch
libc.src.search.remque
+ libc.src.search.tdelete
+ libc.src.search.tdestroy
+ libc.src.search.tfind
+ libc.src.search.tsearch
+ libc.src.search.twalk
+ libc.src.search.twalk_r
# threads.h entrypoints
libc.src.threads.call_once
diff --git a/libc/fuzzing/__support/CMakeLists.txt b/libc/fuzzing/__support/CMakeLists.txt
index 9c674d2fb0d65..f9b49cc1b0a4b 100644
--- a/libc/fuzzing/__support/CMakeLists.txt
+++ b/libc/fuzzing/__support/CMakeLists.txt
@@ -25,6 +25,14 @@ add_libc_fuzzer(
-D__LIBC_EXPLICIT_SIMD_OPT
)
+add_libc_fuzzer(
+ weak_avl_fuzz
+ SRCS
+ weak_avl_fuzz.cpp
+ DEPENDS
+ libc.src.__support.weak_avl
+)
+
# TODO: FreeListHeap uses the _end symbol which conflicts with the _end symbol
# defined by GPU start.cpp files so for now we exclude this fuzzer on GPU.
if(LLVM_LIBC_FULL_BUILD AND NOT LIBC_TARGET_OS_IS_GPU)
diff --git a/libc/fuzzing/__support/weak_avl_fuzz.cpp b/libc/fuzzing/__support/weak_avl_fuzz.cpp
new file mode 100644
index 0000000000000..7c6e50d1fa252
--- /dev/null
+++ b/libc/fuzzing/__support/weak_avl_fuzz.cpp
@@ -0,0 +1,94 @@
+//===-- weak_avl_fuzz.cpp -------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// Fuzzing test for llvm-libc weak AVL implementations.
+///
+//===----------------------------------------------------------------------===//
+#include "hdr/types/ENTRY.h"
+#include "src/__support/CPP/bit.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/weak_avl.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+// A sequence of actions:
+// - Erase: a single byte valued (5, 6 mod 7) followed by an int
+// - Find: a single byte valued (4 mod 7) followed by an int
+// - FindOrInsert: a single byte valued (0,1,2,3 mod 7) followed by an int
+extern "C" size_t LLVMFuzzerMutate(uint8_t *data, size_t size, size_t max_size);
+extern "C" size_t LLVMFuzzerCustomMutator(uint8_t *data, size_t size,
+ size_t max_size, unsigned int seed) {
+ size = LLVMFuzzerMutate(data, size, max_size);
+ return size / (1 + sizeof(int)) * (1 + sizeof(int));
+}
+
+class AVLTree {
+ using Node = WeakAVLNode<int>;
+ Node *root = nullptr;
+ bool reversed = false;
+ static int compare(int a, int b) { return (a > b) - (a < b); }
+ static int reverse_compare(int a, int b) { return (b > a) - (b < a); }
+
+public:
+ AVLTree(bool reversed = false) : reversed(reversed) {}
+ bool find(int key) {
+ return Node::find(root, key, reversed ? reverse_compare : compare);
+ }
+ bool find_or_insert(int key) {
+ return Node::find_or_insert(root, key,
+ reversed ? reverse_compare : compare);
+ }
+ bool erase(int key) {
+ Node *node = Node::find(root, key, reversed ? reverse_compare : compare);
+ if (node)
+ Node::erase(root, node);
+ return node;
+ }
+ ~AVLTree() { Node::destroy(root); }
+};
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+ AVLTree tree1;
+ AVLTree tree2(true);
+ for (size_t i = 0; i + (1 + sizeof(int)) <= size; i += 1 + sizeof(int)) {
+ uint8_t action = data[i];
+ int key;
+ __builtin_memcpy(&key, data + i + 1, sizeof(int));
+ if (action % 7 == 4) {
+ // Find
+ bool res1 = tree1.find(key);
+ bool res2 = tree2.find(key);
+ if (res1 != res2)
+ __builtin_trap();
+
+ } else if (action % 7 == 5 || action % 7 == 6) {
+ // Erase
+ bool res1 = tree1.erase(key);
+ bool res2 = tree2.erase(key);
+ if (res1 != res2)
+ __builtin_trap();
+ if (tree1.find(key))
+ __builtin_trap();
+ if (tree2.find(key))
+ __builtin_trap();
+ } else {
+ // FindOrInsert
+ bool res1 = tree1.find_or_insert(key);
+ bool res2 = tree2.find_or_insert(key);
+ if (res1 != res2)
+ __builtin_trap();
+ if (!tree1.find(key))
+ __builtin_trap();
+ if (!tree2.find(key))
+ __builtin_trap();
+ }
+ }
+ return 0;
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/hdr/types/CMakeLists.txt b/libc/hdr/types/CMakeLists.txt
index 433c47b174766..aed50e64aa2df 100644
--- a/libc/hdr/types/CMakeLists.txt
+++ b/libc/hdr/types/CMakeLists.txt
@@ -487,3 +487,21 @@ add_proxy_header_library(
FULL_BUILD_DEPENDS
libc.include.llvm-libc-types.gid_t
)
+
+add_proxy_header_library(
+ posix_tnode
+ HDRS
+ posix_tnode.h
+ FULL_BUILD_DEPENDS
+ libc.include.llvm-libc-types.posix_tnode
+ libc.include.search
+)
+
+add_proxy_header_library(
+ VISIT
+ HDRS
+ VISIT.h
+ FULL_BUILD_DEPENDS
+ libc.include.llvm-libc-types.VISIT
+ libc.include.search
+)
diff --git a/libc/hdr/types/VISIT.h b/libc/hdr/types/VISIT.h
new file mode 100644
index 0000000000000..e8377c233267c
--- /dev/null
+++ b/libc/hdr/types/VISIT.h
@@ -0,0 +1,22 @@
+//===-- Definition of macros from VISIT -----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_HDR_TYPES_VISIT_H
+#define LLVM_LIBC_HDR_TYPES_VISIT_H
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-types/VISIT.h"
+
+#else // Overlay mode
+
+#include <search.h>
+
+#endif // LLVM_LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_TYPES_VISIT_H
diff --git a/libc/hdr/types/posix_tnode.h b/libc/hdr/types/posix_tnode.h
new file mode 100644
index 0000000000000..0b2ecfd488217
--- /dev/null
+++ b/libc/hdr/types/posix_tnode.h
@@ -0,0 +1,28 @@
+//===-- Definition of macros from posix_tnode -----------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_HDR_TYPES_POSIX_TNODE_H
+#define LLVM_LIBC_HDR_TYPES_POSIX_TNODE_H
+
+// posix_tnode is introduced in POSIX.1-2024.
+// this may result in problems when overlaying on older systems.
+// internal code should use __llvm_libc_tnode.
+
+#ifdef LIBC_FULL_BUILD
+
+#include "include/llvm-libc-types/posix_tnode.h"
+#define __llvm_libc_tnode posix_tnode
+
+#else // Overlay mode
+
+#include <search.h>
+typedef void __llvm_libc_tnode;
+
+#endif // LLVM_LIBC_FULL_BUILD
+
+#endif // LLVM_LIBC_HDR_TYPES_POSIX_TNODE_H
diff --git a/libc/include/CMakeLists.txt b/libc/include/CMakeLists.txt
index 96c3a88f3fcc8..c72bb5a6eb280 100644
--- a/libc/include/CMakeLists.txt
+++ b/libc/include/CMakeLists.txt
@@ -273,9 +273,13 @@ add_header_macro(
.llvm-libc-types.ACTION
.llvm-libc-types.ENTRY
.llvm-libc-types.VISIT
+ .llvm-libc-types.posix_tnode
.llvm-libc-types.__search_compare_t
.llvm-libc-types.size_t
.llvm-libc-types.struct_hsearch_data
+ .llvm-libc-types.__action_closure_fn_t
+ .llvm-libc-types.__action_fn_t
+ .llvm-libc-types.__free_fn_t
.llvm_libc_common_h
)
diff --git a/libc/include/llvm-libc-types/CMakeLists.txt b/libc/include/llvm-libc-types/CMakeLists.txt
index fcd0e1245a4a8..0c6d4d8e870d3 100644
--- a/libc/include/llvm-libc-types/CMakeLists.txt
+++ b/libc/include/llvm-libc-types/CMakeLists.txt
@@ -52,6 +52,7 @@ add_header(off_t HDR off_t.h)
add_header(once_flag HDR once_flag.h DEPENDS .__futex_word)
add_header(posix_spawn_file_actions_t HDR posix_spawn_file_actions_t.h)
add_header(posix_spawnattr_t HDR posix_spawnattr_t.h)
+add_header(posix_tnode HDR posix_tnode.h)
add_header(pthread_attr_t HDR pthread_attr_t.h DEPENDS .size_t)
add_header(pthread_condattr_t HDR pthread_condattr_t.h DEPENDS .clockid_t)
add_header(pthread_key_t HDR pthread_key_t.h)
@@ -310,3 +311,18 @@ add_header(EFI_SYSTEM_TABLE
.EFI_TABLE_HEADER
.char16_t
)
+add_header(__action_closure_fn_t
+ HDR
+ __action_closure_fn_t.h
+ DEPENDS
+ .posix_tnode
+ .VISIT
+)
+add_header(__action_fn_t
+ HDR
+ __action_fn_t.h
+ DEPENDS
+ .posix_tnode
+ .VISIT
+)
+add_header(__free_fn_t HDR __free_fn_t.h)
diff --git a/libc/include/llvm-libc-types/__action_closure_fn_t.h b/libc/include/llvm-libc-types/__action_closure_fn_t.h
new file mode 100644
index 0000000000000..18d91a3f53925
--- /dev/null
+++ b/libc/include/llvm-libc-types/__action_closure_fn_t.h
@@ -0,0 +1,17 @@
+//===-- Definition of type __action_closure_fn_t --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TYPES___ACTION_CLOSURE_FN_T_H
+#define LLVM_LIBC_TYPES___ACTION_CLOSURE_FN_T_H
+
+#include "VISIT.h"
+#include "posix_tnode.h"
+
+typedef void (*__action_closure_fn_t)(const posix_tnode *, VISIT, void *);
+
+#endif // LLVM_LIBC_TYPES___ACTION_CLOSURE_FN_T_H
diff --git a/libc/include/llvm-libc-types/__action_fn_t.h b/libc/include/llvm-libc-types/__action_fn_t.h
new file mode 100644
index 0000000000000..de3dc02e4eacd
--- /dev/null
+++ b/libc/include/llvm-libc-types/__action_fn_t.h
@@ -0,0 +1,17 @@
+//===-- Definition of type __action_fn_t ----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TYPES___ACTION_FN_T_H
+#define LLVM_LIBC_TYPES___ACTION_FN_T_H
+
+#include "VISIT.h"
+#include "posix_tnode.h"
+
+typedef void (*__action_fn_t)(const posix_tnode *, VISIT, int);
+
+#endif // LLVM_LIBC_TYPES___ACTION_FN_T_H
diff --git a/libc/include/llvm-libc-types/__free_fn_t.h b/libc/include/llvm-libc-types/__free_fn_t.h
new file mode 100644
index 0000000000000..72f00f3df5796
--- /dev/null
+++ b/libc/include/llvm-libc-types/__free_fn_t.h
@@ -0,0 +1,14 @@
+//===-- Definition of type __free_fn_t ------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TYPES___FREE_FN_T_H
+#define LLVM_LIBC_TYPES___FREE_FN_T_H
+
+typedef void (*__free_fn_t)(void *);
+
+#endif // LLVM_LIBC_TYPES___FREE_FN_T_H
diff --git a/libc/include/llvm-libc-types/posix_tnode.h b/libc/include/llvm-libc-types/posix_tnode.h
new file mode 100644
index 0000000000000..0f7336ac2ad89
--- /dev/null
+++ b/libc/include/llvm-libc-types/posix_tnode.h
@@ -0,0 +1,17 @@
+//===-- Definition of type posix_tnode--------------- ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_TYPES_POSIX_TNODE_H
+#define LLVM_LIBC_TYPES_POSIX_TNODE_H
+
+// Following POSIX.1-2024 and Austin Group Defect Report 1011:
+// https://austingroupbugs.net/view.php?id=1011
+// Define posix_tnode as void to provide both type safety and compatibility.
+typedef void posix_tnode;
+
+#endif // LLVM_LIBC_TYPES_POSIX_TNODE_H
diff --git a/libc/include/search.yaml b/libc/include/search.yaml
index 8a3a0c50af60f..50f317820e1b5 100644
--- a/libc/include/search.yaml
+++ b/libc/include/search.yaml
@@ -7,6 +7,10 @@ types:
- type_name: VISIT
- type_name: __search_compare_t
- type_name: struct_hsearch_data
+ - type_name: posix_tnode
+ - type_name: __action_closure_fn_t
+ - type_name: __action_fn_t
+ - type_name: __free_fn_t
enums: []
objects: []
functions:
@@ -80,3 +84,47 @@ functions:
- type: size_t *
- type: size_t
- type: __search_compare_t
+ - name: tdelete
+ standards:
+ - posix
+ return_type: void *
+ arguments:
+ - type: const void *__restrict
+ - type: posix_tnode **__restrict
+ - type: __search_compare_t
+ - name: tfind
+ standards:
+ - posix
+ return_type: posix_tnode *
+ arguments:
+ - type: const void *
+ - type: posix_tnode * const *
+ - type: __search_compare_t
+ - name: tsearch
+ standards:
+ - posix
+ return_type: posix_tnode *
+ arguments:
+ - type: const void *
+ - type: posix_tnode **
+ - type: __search_compare_t
+ - name: twalk
+ standards:
+ - posix
+ return_type: void
+ arguments:
+ - type: const posix_tnode *
+ - type: __action_fn_t
+ - name: twalk_r
+ standards: gnu
+ return_type: void
+ arguments:
+ - type: const posix_tnode *
+ - type: __action_closure_fn_t
+ - type: void *
+ - name: tdestroy
+ standards: gnu
+ return_type: void
+ arguments:
+ - type: posix_tnode *
+ - type: __free_fn_t
diff --git a/libc/src/__support/CMakeLists.txt b/libc/src/__support/CMakeLists.txt
index c7f127d6934a0..bde12abaa291e 100644
--- a/libc/src/__support/CMakeLists.txt
+++ b/libc/src/__support/CMakeLists.txt
@@ -391,6 +391,20 @@ add_header_library(
libc.src.__support.macros.attributes
)
+add_header_library(
+ weak_avl
+ HDRS
+ weak_avl.h
+ DEPENDS
+ libc.hdr.stdint_proxy
+ libc.src.__support.CPP.bit
+ libc.src.__support.CPP.new
+ libc.src.__support.CPP.utility
+ libc.src.__support.libc_assert
+ libc.src.__support.macros.attributes
+ libc.src.__support.macros.config
+)
+
add_subdirectory(FPUtil)
add_subdirectory(OSUtil)
add_subdirectory(StringUtil)
diff --git a/libc/src/__support/weak_avl.h b/libc/src/__support/weak_avl.h
new file mode 100644
index 0000000000000..6ad85ca4b9b8f
--- /dev/null
+++ b/libc/src/__support/weak_avl.h
@@ -0,0 +1,595 @@
+//===-- Implementation header for weak AVL tree -----------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_WEAK_AVL_H
+#define LLVM_LIBC_SRC___SUPPORT_WEAK_AVL_H
+
+#include "hdr/stdint_proxy.h"
+#include "src/__support/CPP/bit.h"
+#include "src/__support/CPP/new.h"
+#include "src/__support/CPP/utility/move.h"
+#include "src/__support/libc_assert.h"
+#include "src/__support/macros/attributes.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+// A general self-balancing binary search tree where the node pointer can
+// be used as stable handles to the stored values.
+//
+// The self-balancing strategy is the Weak AVL (WAVL) tree, based on the
+// following foundational references:
+// 1. https://maskray.me/blog/2025-12-14-weak-avl-tree
+// 2. https://reviews.freebsd.org/D25480
+// 3. https://ics.uci.edu/~goodrich/teach/cs165/notes/WeakAVLTrees.pdf
+// 4. https://dl.acm.org/doi/10.1145/2689412 (Rank-Balanced Trees)
+//
+// WAVL trees belong to the rank-balanced binary search tree framework
+// (reference 4), alongside AVL and Red-Black trees.
+//
+// Key Properties of WAVL Trees:
+// 1. Relationship to Red-Black Trees: A WAVL tree can always be colored as a
+// Red-Black tree.
+// 2. Relationship to AVL Trees: An AVL tree meets all the requirements of a
+// WAVL tree. Insertion-only WAVL trees maintain the same structure as AVL
+// trees.
+//
+// Rank-Based Balancing:
+// In rank-balanced trees, each node is assigned a rank (conceptually similar
+// to height). The rank difference between a parent and its child is
+// strictly enforced to be either **1** or **2**.
+//
+// - **AVL Trees:** Rank is equivalent to height. The strict condition is that
+// there are no 2-2 nodes (a parent with rank difference 2 to both children).
+// - **WAVL Trees:** The no 2-2 node rule is relaxed for internal nodes during
+// the deletion fixup process, making WAVL trees less strictly balanced than
+// AVL trees but easier to maintain than Red-Black trees.
+//
+// Balancing Mechanics (Promotion/Demotion):
+// - **Null nodes** are considered to have rank -1.
+// - **External/leaf nodes** have rank 0.
+// - **Insertion:** Inserting a node may create a situation where a parent and
+// child have the same rank (difference 0). This is fixed by **promoting**
+// the rank of the parent and propagating the fix upwards using at most two
+// rotations (trinode fixup).
+// - **Deletion:** Deleting a node may result in a parent being 3 ranks higher
+// than a child (difference 3). This is fixed by **demoting** the parent's
+// rank and propagating the fix upwards.
+//
+// Implementation Detail:
+// The rank is **implicitly** maintained. We never store the full rank. Instead,
+// a 2-bit tag is used on each node to record the rank difference to each child:
+// - Bit cleared (0) -> Rank difference is **1**.
+// - Bit set (1) -> Rank difference is **2**.
+template <typename T> class WeakAVLNode {
+ // Data
+ T data;
+
+ // Parent pointer
+ WeakAVLNode *parent;
+
+ // Children pointers
+ WeakAVLNode *children[2];
+
+ // Flags
+ unsigned char left_rank_diff_2 : 1;
+ unsigned char right_rank_diff_2 : 1;
+
+ LIBC_INLINE bool is_leaf() const {
+ return (children[0] == nullptr) && (children[1] == nullptr);
+ }
+
+ LIBC_INLINE void toggle_rank_diff_2(bool is_right) {
+ if (is_right)
+ right_rank_diff_2 ^= 1;
+ else
+ left_rank_diff_2 ^= 1;
+ }
+
+ LIBC_INLINE bool both_flags_set() const {
+ return left_rank_diff_2 && right_rank_diff_2;
+ }
+
+ LIBC_INLINE bool any_flag_set() const {
+ return left_rank_diff_2 || right_rank_diff_2;
+ }
+
+ LIBC_INLINE void clear_flags() {
+ left_rank_diff_2 = 0;
+ right_rank_diff_2 = 0;
+ }
+
+ LIBC_INLINE void set_both_flags() {
+ left_rank_diff_2 = 1;
+ right_rank_diff_2 = 1;
+ }
+
+ LIBC_INLINE WeakAVLNode(T data)
+ : data(cpp::move(data)), parent(nullptr), children{nullptr, nullptr},
+ left_rank_diff_2(0), right_rank_diff_2(0) {}
+
+ LIBC_INLINE static WeakAVLNode *create(T value) {
+ AllocChecker ac;
+ WeakAVLNode *res = new (ac) WeakAVLNode(value);
+ if (ac)
+ return res;
+ return nullptr;
+ }
+
+ // Unlink a node from tree. The corresponding flag is not updated. The node is
+ // not deleted and its pointers are not cleared.
+ // FixupSite is the lowest surviving node from which rank/flag invariants may
+ // be violated.
+ // Our tree requires value to stay in their node to maintain stable addresses.
+ // This complicates the unlink operation as the successor transplanting needs
+ // to update all the pointers and flags.
+ struct FixupSite {
+ WeakAVLNode *parent;
+ ...
[truncated]
|
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