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1//===------------------------ __refstring ---------------------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is dual licensed under the MIT and the University of Illinois Open
6// Source Licenses. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10#ifndef _LIBCPP___REFSTRING
11#define _LIBCPP___REFSTRING
12
13#include <__config>
14#include <cstddef>
15#include <cstring>
16#if __APPLE__
17#include <dlfcn.h>
18#include <mach-o/dyld.h>
19#endif
20
21_LIBCPP_BEGIN_NAMESPACE_STD
22
23class _LIBCPP_HIDDEN __libcpp_refstring
24{
25private:
26    const char* str_;
27
28    typedef int count_t;
29
30    struct _Rep_base
31    {
32        std::size_t len;
33        std::size_t cap;
34        count_t     count;
35    };
36
37    static
38    _Rep_base*
39    rep_from_data(const char *data_) _NOEXCEPT
40    {
41        char *data = const_cast<char *>(data_);
42        return reinterpret_cast<_Rep_base *>(data - sizeof(_Rep_base));
43    }
44    static
45    char *
46    data_from_rep(_Rep_base *rep) _NOEXCEPT
47    {
48        char *data = reinterpret_cast<char *>(rep);
49        return data + sizeof(*rep);
50    }
51
52#if __APPLE__
53    static
54    const char*
55    compute_gcc_empty_string_storage() _NOEXCEPT
56    {
57        void* handle = dlopen("/usr/lib/libstdc++.6.dylib", RTLD_NOLOAD);
58        if (handle == nullptr)
59            return nullptr;
60        void* sym = dlsym(handle, "_ZNSs4_Rep20_S_empty_rep_storageE");
61        if (sym == nullptr)
62            return nullptr;
63        return data_from_rep(reinterpret_cast<_Rep_base *>(sym));
64    }
65
66    static
67    const char*
68    get_gcc_empty_string_storage() _NOEXCEPT
69    {
70        static const char* p = compute_gcc_empty_string_storage();
71        return p;
72    }
73
74    bool
75    uses_refcount() const
76    {
77        return str_ != get_gcc_empty_string_storage();
78    }
79#else
80    bool
81    uses_refcount() const
82    {
83        return true;
84    }
85#endif
86
87public:
88    explicit __libcpp_refstring(const char* msg) {
89        std::size_t len = strlen(msg);
90        _Rep_base* rep = static_cast<_Rep_base *>(::operator new(sizeof(*rep) + len + 1));
91        rep->len = len;
92        rep->cap = len;
93        rep->count = 0;
94        char *data = data_from_rep(rep);
95        std::memcpy(data, msg, len + 1);
96        str_ = data;
97    }
98
99    __libcpp_refstring(const __libcpp_refstring& s) _NOEXCEPT : str_(s.str_)
100    {
101        if (uses_refcount())
102            __sync_add_and_fetch(&rep_from_data(str_)->count, 1);
103    }
104
105    __libcpp_refstring& operator=(const __libcpp_refstring& s) _NOEXCEPT
106    {
107        bool adjust_old_count = uses_refcount();
108        struct _Rep_base *old_rep = rep_from_data(str_);
109        str_ = s.str_;
110        if (uses_refcount())
111            __sync_add_and_fetch(&rep_from_data(str_)->count, 1);
112        if (adjust_old_count)
113        {
114            if (__sync_add_and_fetch(&old_rep->count, count_t(-1)) < 0)
115            {
116                ::operator delete(old_rep);
117            }
118        }
119        return *this;
120    }
121
122    ~__libcpp_refstring()
123    {
124        if (uses_refcount())
125        {
126            _Rep_base* rep = rep_from_data(str_);
127            if (__sync_add_and_fetch(&rep->count, count_t(-1)) < 0)
128            {
129                ::operator delete(rep);
130            }
131        }
132    }
133
134    const char* c_str() const _NOEXCEPT {return str_;}
135};
136
137_LIBCPP_END_NAMESPACE_STD
138
139#endif //_LIBCPP___REFSTRING
140