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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 #ifdef __APPLE__
     17 #include <dlfcn.h>
     18 #include <mach-o/dyld.h>
     19 #endif
     20 
     21 _LIBCPP_BEGIN_NAMESPACE_STD
     22 
     23 class _LIBCPP_HIDDEN __libcpp_refstring
     24 {
     25 private:
     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 #ifdef __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 
     87 public:
     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