Import C++ Standard Template Library

You can now use the hardest fastest and most dangerous language there is
with Cosmopolitan. So far about 75% of LLVM libcxx has been added. A few
breaking changes needed to be made to help this go smoothly.

- Rename nothrow to dontthrow
- Rename nodiscard to dontdiscard
- Add some libm functions, e.g. lgamma, nan, etc.
- Change intmax_t from int128 to int64 like everything else
- Introduce %jjd formatting directive for int128_t
- Introduce strtoi128(), strtou128(), etc.
- Rename bsrmax() to bsr128()

Some of the templates that should be working currently are std::vector,
std::string, std::map, std::set, std::deque, etc.

third_party/libcxx/refstring.hh

@@ -0,0 +1,114 @@
+//===------------------------ __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 "third_party/libcxx/__config"
+#include "third_party/libcxx/stdexcept"
+#include "third_party/libcxx/cstddef"
+#include "third_party/libcxx/cstring"
+#include "third_party/libcxx/atomic_support.hh"
+
+_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
+} // 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