base/internal/hide_ptr.h

0001 // Copyright 2018 The Abseil Authors.
0002 //
0003 // Licensed under the Apache License, Version 2.0 (the "License");
0004 // you may not use this file except in compliance with the License.
0005 // You may obtain a copy of the License at
0006 //
0007 //      https://www.apache.org/licenses/LICENSE-2.0
0008 //
0009 // Unless required by applicable law or agreed to in writing, software
0010 // distributed under the License is distributed on an "AS IS" BASIS,
0011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
0012 // See the License for the specific language governing permissions and
0013 // limitations under the License.
0014
0015 #ifndef ABSL_BASE_INTERNAL_HIDE_PTR_H_
0016 #define ABSL_BASE_INTERNAL_HIDE_PTR_H_
0017
0018 #include <cstdint>
0019
0020 #include "absl/base/config.h"
0021
0022 namespace absl {
0023 ABSL_NAMESPACE_BEGIN
0024 namespace base_internal {
0025
0026 // Arbitrary value with high bits set. Xor'ing with it is unlikely
0027 // to map one valid pointer to another valid pointer.
0028 constexpr uintptr_t HideMask() {
0029   return (uintptr_t{0xF03A5F7BU} << (sizeof(uintptr_t) - 4) * 8) | 0xF03A5F7BU;
0030 }
0031
0032 // Hide a pointer from the leak checker. For internal use only.
0033 // Differs from absl::IgnoreLeak(ptr) in that absl::IgnoreLeak(ptr) causes ptr
0034 // and all objects reachable from ptr to be ignored by the leak checker.
0035 template <class T>
0036 inline uintptr_t HidePtr(T* ptr) {
0037   return reinterpret_cast<uintptr_t>(ptr) ^ HideMask();
0038 }
0039
0040 // Return a pointer that has been hidden from the leak checker.
0041 // For internal use only.
0042 template <class T>
0043 inline T* UnhidePtr(uintptr_t hidden) {
0044   return reinterpret_cast<T*>(hidden ^ HideMask());
0045 }
0046
0047 }  // namespace base_internal
0048 ABSL_NAMESPACE_END
0049 }  // namespace absl
0050
0051 #endif  // ABSL_BASE_INTERNAL_HIDE_PTR_H_