refstring.h
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//===------------------------ __refstring ---------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCPP_REFSTRING_H
#define _LIBCPP_REFSTRING_H
#include <__config>
#include <stdexcept>
#include <cstddef>
#include <cstring>
#ifdef __APPLE__
#include <dlfcn.h>
#include <mach-o/dyld.h>
#endif
#include "atomic_support.h"
_LIBCPP_BEGIN_NAMESPACE_STD
namespace __refstring_imp { namespace {
typedef int count_t;
struct _Rep_base {
std::size_t len;
std::size_t cap;
count_t count;
};
inline _Rep_base* rep_from_data(const char *data_) noexcept {
char *data = const_cast<char *>(data_);
return reinterpret_cast<_Rep_base *>(data - sizeof(_Rep_base));
}
inline char * data_from_rep(_Rep_base *rep) noexcept {
char *data = reinterpret_cast<char *>(rep);
return data + sizeof(*rep);
}
#if defined(__APPLE__)
inline
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));
}
inline
const char*
get_gcc_empty_string_storage() _NOEXCEPT
{
static const char* p = compute_gcc_empty_string_storage();
return p;
}
#endif
}} // namespace __refstring_imp
using namespace __refstring_imp;
inline
__libcpp_refstring::__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);
__imp_ = data;
}
inline
__libcpp_refstring::__libcpp_refstring(const __libcpp_refstring &s) _NOEXCEPT
: __imp_(s.__imp_)
{
if (__uses_refcount())
__libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
}
inline
__libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring const& s) _NOEXCEPT {
bool adjust_old_count = __uses_refcount();
struct _Rep_base *old_rep = rep_from_data(__imp_);
__imp_ = s.__imp_;
if (__uses_refcount())
__libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
if (adjust_old_count)
{
if (__libcpp_atomic_add(&old_rep->count, count_t(-1)) < 0)
{
::operator delete(old_rep);
}
}
return *this;
}
inline
__libcpp_refstring::~__libcpp_refstring() {
if (__uses_refcount()) {
_Rep_base* rep = rep_from_data(__imp_);
if (__libcpp_atomic_add(&rep->count, count_t(-1)) < 0) {
::operator delete(rep);
}
}
}
inline
bool __libcpp_refstring::__uses_refcount() const {
#ifdef __APPLE__
return __imp_ != get_gcc_empty_string_storage();
#else
return true;
#endif
}
_LIBCPP_END_NAMESPACE_STD
#endif //_LIBCPP_REFSTRING_H