include/__refstring

//===------------------------ __refstring ---------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___REFSTRING
#define _LIBCPP___REFSTRING

#include <__config>
#include <cstddef>
#include <cstring>
#ifdef __APPLE__
#include <dlfcn.h>
#include <mach-o/dyld.h>
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

class _LIBCPP_HIDDEN __libcpp_refstring
{
private:
 const char* str_;

 typedef int count_t;

 struct _Rep_base
 {
 std::size_t len;
 std::size_t cap;
 count_t count;
 };

 static
 _Rep_base*
 rep_from_data(const char *data_) _NOEXCEPT
 {
 char *data = const_cast<char *>(data_);
 return reinterpret_cast<_Rep_base *>(data - sizeof(_Rep_base));
 }
 static
 char *
 data_from_rep(_Rep_base *rep) _NOEXCEPT
 {
 char *data = reinterpret_cast<char *>(rep);
 return data + sizeof(*rep);
 }

#ifdef __APPLE__
 static
 const char*
 compute_gcc_empty_string_storage() _NOEXCEPT
 {
 void* handle = dlopen("/usr/lib/libstdc++.6.dylib", RTLD_NOLOAD);
 if (handle == nullptr)
 return nullptr;
 void* sym = dlsym(handle, "_ZNSs4_Rep20_S_empty_rep_storageE");
 if (sym == nullptr)
 return nullptr;
 return data_from_rep(reinterpret_cast<_Rep_base *>(sym));
 }

 static
 const char*
 get_gcc_empty_string_storage() _NOEXCEPT
 {
 static const char* p = compute_gcc_empty_string_storage();
 return p;
 }

 bool
 uses_refcount() const
 {
 return str_ != get_gcc_empty_string_storage();
 }
#else
 bool
 uses_refcount() const
 {
 return true;
 }
#endif

public:
 explicit __libcpp_refstring(const char* msg) {
 std::size_t len = strlen(msg);
 _Rep_base* rep = static_cast<_Rep_base *>(::operator new(sizeof(*rep) + len + 1));
 rep->len = len;
 rep->cap = len;
 rep->count = 0;
 char *data = data_from_rep(rep);
 std::memcpy(data, msg, len + 1);
 str_ = data;
 }

 __libcpp_refstring(const __libcpp_refstring& s) _NOEXCEPT : str_(s.str_)
 {
 if (uses_refcount())
 __sync_add_and_fetch(&rep_from_data(str_)->count, 1);
 }

 __libcpp_refstring& operator=(const __libcpp_refstring& s) _NOEXCEPT
 {
 bool adjust_old_count = uses_refcount();
 struct _Rep_base *old_rep = rep_from_data(str_);
 str_ = s.str_;
 if (uses_refcount())
 __sync_add_and_fetch(&rep_from_data(str_)->count, 1);
 if (adjust_old_count)
 {
 if (__sync_add_and_fetch(&old_rep->count, count_t(-1)) < 0)
 {
 ::operator delete(old_rep);
 }
 }
 return *this;
 }

 ~__libcpp_refstring()
 {
 if (uses_refcount())
 {
 _Rep_base* rep = rep_from_data(str_);
 if (__sync_add_and_fetch(&rep->count, count_t(-1)) < 0)
 {
 ::operator delete(rep);
 }
 }
 }

 const char* c_str() const _NOEXCEPT {return str_;}
};

_LIBCPP_END_NAMESPACE_STD

#endif //_LIBCPP___REFSTRING