1//===------------------------ __refstring ---------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP_REFSTRING_H
10#define _LIBCPP_REFSTRING_H
11
12#include <__config>
13#include <stdexcept>
14#include <cstddef>
15#include <cstring>
16#ifdef __APPLE__
17#include <dlfcn.h>
18#include <mach-o/dyld.h>
19#endif
20#include "atomic_support.h"
21
22_LIBCPP_BEGIN_NAMESPACE_STD
23
24namespace __refstring_imp { namespace {
25typedef int count_t;
26
27struct _Rep_base {
28 std::size_t len;
29 std::size_t cap;
30 count_t count;
31};
32
33inline _Rep_base* rep_from_data(const char *data_) noexcept {
34 char *data = const_cast<char *>(data_);
35 return reinterpret_cast<_Rep_base *>(data - sizeof(_Rep_base));
36}
37
38inline char * data_from_rep(_Rep_base *rep) noexcept {
39 char *data = reinterpret_cast<char *>(rep);
40 return data + sizeof(*rep);
41}
42
43#if defined(__APPLE__)
44inline
45const char* compute_gcc_empty_string_storage() _NOEXCEPT
46{
47 void* handle = dlopen("/usr/lib/libstdc++.6.dylib", RTLD_NOLOAD);
48 if (handle == nullptr)
49 return nullptr;
50 void* sym = dlsym(handle, "_ZNSs4_Rep20_S_empty_rep_storageE");
51 if (sym == nullptr)
52 return nullptr;
53 return data_from_rep(reinterpret_cast<_Rep_base *>(sym));
54}
55
56inline
57const char*
58get_gcc_empty_string_storage() _NOEXCEPT
59{
60 static const char* p = compute_gcc_empty_string_storage();
61 return p;
62}
63#endif
64
65}} // namespace __refstring_imp
66
67using namespace __refstring_imp;
68
69inline
70__libcpp_refstring::__libcpp_refstring(const char* msg) {
71 std::size_t len = strlen(msg);
72 _Rep_base* rep = static_cast<_Rep_base *>(::operator new(sizeof(*rep) + len + 1));
73 rep->len = len;
74 rep->cap = len;
75 rep->count = 0;
76 char *data = data_from_rep(rep);
77 std::memcpy(data, msg, len + 1);
78 __imp_ = data;
79}
80
81inline
82__libcpp_refstring::__libcpp_refstring(const __libcpp_refstring &s) _NOEXCEPT
83 : __imp_(s.__imp_)
84{
85 if (__uses_refcount())
86 __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
87}
88
89inline
90__libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring const& s) _NOEXCEPT {
91 bool adjust_old_count = __uses_refcount();
92 struct _Rep_base *old_rep = rep_from_data(__imp_);
93 __imp_ = s.__imp_;
94 if (__uses_refcount())
95 __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
96 if (adjust_old_count)
97 {
98 if (__libcpp_atomic_add(&old_rep->count, count_t(-1)) < 0)
99 {
100 ::operator delete(old_rep);
101 }
102 }
103 return *this;
104}
105
106inline
107__libcpp_refstring::~__libcpp_refstring() {
108 if (__uses_refcount()) {
109 _Rep_base* rep = rep_from_data(__imp_);
110 if (__libcpp_atomic_add(&rep->count, count_t(-1)) < 0) {
111 ::operator delete(rep);
112 }
113 }
114}
115
116inline
117bool __libcpp_refstring::__uses_refcount() const {
118#ifdef __APPLE__
119 return __imp_ != get_gcc_empty_string_storage();
120#else
121 return true;
122#endif
123}
124
125_LIBCPP_END_NAMESPACE_STD
126
127#endif //_LIBCPP_REFSTRING_H
128