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authorChris Palmer <palmer@chromium.org>2017-03-16 11:39:48 -0700
committerChromium commit bot <commit-bot@chromium.org>2017-03-16 19:59:52 +0000
commit79e548eb98caefd3ea0f0e4806a7abca6654e7dc (patch)
treeb72d07ae05f7fa06da7ad8ef0b733d403457903f /third_party/base/template_util.h
parent5e67ce37b4df8127a28644d312f194ca8fc63585 (diff)
downloadpdfium-79e548eb98caefd3ea0f0e4806a7abca6654e7dc.tar.xz
Import PartitionAlloc from Chromium.
We'll add callers in a later CL. BUG=pdfium:678 Change-Id: I98c8b2832c4750df326218e24ee8c1bd33b89b50 Reviewed-on: https://pdfium-review.googlesource.com/3066 Commit-Queue: Tom Sepez <tsepez@chromium.org> Reviewed-by: Tom Sepez <tsepez@chromium.org>
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+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_TEMPLATE_UTIL_H_
+#define BASE_TEMPLATE_UTIL_H_
+
+#include <stddef.h>
+#include <iosfwd>
+#include <type_traits>
+#include <utility>
+
+#include "third_party/build/build_config.h"
+
+// This hacks around libstdc++ 4.6 missing stuff in type_traits, while we need
+// to support it.
+#define CR_GLIBCXX_4_7_0 20120322
+#define CR_GLIBCXX_4_5_4 20120702
+#define CR_GLIBCXX_4_6_4 20121127
+#if defined(__GLIBCXX__) && \
+ (__GLIBCXX__ < CR_GLIBCXX_4_7_0 || __GLIBCXX__ == CR_GLIBCXX_4_5_4 || \
+ __GLIBCXX__ == CR_GLIBCXX_4_6_4)
+#define CR_USE_FALLBACKS_FOR_OLD_GLIBCXX
+#endif
+
+// Some versions of libstdc++ have partial support for type_traits, but misses
+// a smaller subset while removing some of the older non-standard stuff. Assume
+// that all versions below 5.0 fall in this category, along with one 5.0
+// experimental release. Test for this by consulting compiler major version,
+// the only reliable option available, so theoretically this could fail should
+// you attempt to mix an earlier version of libstdc++ with >= GCC5. But
+// that's unlikely to work out, especially as GCC5 changed ABI.
+#define CR_GLIBCXX_5_0_0 20150123
+#if (defined(__GNUC__) && __GNUC__ < 5) || \
+ (defined(__GLIBCXX__) && __GLIBCXX__ == CR_GLIBCXX_5_0_0)
+#define CR_USE_FALLBACKS_FOR_OLD_EXPERIMENTAL_GLIBCXX
+#endif
+
+// This hacks around using gcc with libc++ which has some incompatibilies.
+// - is_trivially_* doesn't work: https://llvm.org/bugs/show_bug.cgi?id=27538
+// TODO(danakj): Remove this when android builders are all using a newer version
+// of gcc, or the android ndk is updated to a newer libc++ that works with older
+// gcc versions.
+#if !defined(__clang__) && defined(_LIBCPP_VERSION)
+#define CR_USE_FALLBACKS_FOR_GCC_WITH_LIBCXX
+#endif
+
+namespace base {
+
+template <class T>
+struct is_non_const_reference : std::false_type {};
+template <class T>
+struct is_non_const_reference<T&> : std::true_type {};
+template <class T>
+struct is_non_const_reference<const T&> : std::false_type {};
+
+// is_assignable
+
+namespace internal {
+
+template <typename First, typename Second>
+struct SelectSecond {
+ using type = Second;
+};
+
+struct Any {
+ Any(...);
+};
+
+// True case: If |Lvalue| can be assigned to from |Rvalue|, then the return
+// value is a true_type.
+template <class Lvalue, class Rvalue>
+typename internal::SelectSecond<
+ decltype((std::declval<Lvalue>() = std::declval<Rvalue>())),
+ std::true_type>::type
+IsAssignableTest(Lvalue&&, Rvalue&&);
+
+// False case: Otherwise the return value is a false_type.
+template <class Rvalue>
+std::false_type IsAssignableTest(internal::Any, Rvalue&&);
+
+// Default case: Neither Lvalue nor Rvalue is void. Uses IsAssignableTest to
+// determine the type of IsAssignableImpl.
+template <class Lvalue,
+ class Rvalue,
+ bool = std::is_void<Lvalue>::value || std::is_void<Rvalue>::value>
+struct IsAssignableImpl
+ : public std::common_type<decltype(
+ internal::IsAssignableTest(std::declval<Lvalue>(),
+ std::declval<Rvalue>()))>::type {};
+
+// Void case: Either Lvalue or Rvalue is void. Then the type of IsAssignableTest
+// is false_type.
+template <class Lvalue, class Rvalue>
+struct IsAssignableImpl<Lvalue, Rvalue, true> : public std::false_type {};
+
+// Uses expression SFINAE to detect whether using operator<< would work.
+template <typename T, typename = void>
+struct SupportsOstreamOperator : std::false_type {};
+template <typename T>
+struct SupportsOstreamOperator<T,
+ decltype(void(std::declval<std::ostream&>()
+ << std::declval<T>()))>
+ : std::true_type {};
+
+} // namespace internal
+
+// TODO(crbug.com/554293): Remove this when all platforms have this in the std
+// namespace.
+template <class Lvalue, class Rvalue>
+struct is_assignable : public internal::IsAssignableImpl<Lvalue, Rvalue> {};
+
+// is_copy_assignable is true if a T const& is assignable to a T&.
+// TODO(crbug.com/554293): Remove this when all platforms have this in the std
+// namespace.
+template <class T>
+struct is_copy_assignable
+ : public is_assignable<typename std::add_lvalue_reference<T>::type,
+ typename std::add_lvalue_reference<
+ typename std::add_const<T>::type>::type> {};
+
+// is_move_assignable is true if a T&& is assignable to a T&.
+// TODO(crbug.com/554293): Remove this when all platforms have this in the std
+// namespace.
+template <class T>
+struct is_move_assignable
+ : public is_assignable<typename std::add_lvalue_reference<T>::type,
+ const typename std::add_rvalue_reference<T>::type> {
+};
+
+// underlying_type produces the integer type backing an enum type.
+// TODO(crbug.com/554293): Remove this when all platforms have this in the std
+// namespace.
+#if defined(CR_USE_FALLBACKS_FOR_OLD_GLIBCXX)
+template <typename T>
+struct underlying_type {
+ using type = __underlying_type(T);
+};
+#else
+template <typename T>
+using underlying_type = std::underlying_type<T>;
+#endif
+
+// TODO(crbug.com/554293): Remove this when all platforms have this in the std
+// namespace.
+#if defined(CR_USE_FALLBACKS_FOR_OLD_GLIBCXX)
+template <class T>
+using is_trivially_destructible = std::has_trivial_destructor<T>;
+#else
+template <class T>
+using is_trivially_destructible = std::is_trivially_destructible<T>;
+#endif
+
+// is_trivially_copyable is especially hard to get right.
+// - Older versions of libstdc++ will fail to have it like they do for other
+// type traits. In this case we should provide it based on compiler
+// intrinsics. This is covered by the CR_USE_FALLBACKS_FOR_OLD_GLIBCXX define.
+// - An experimental release of gcc includes most of type_traits but misses
+// is_trivially_copyable, so we still have to avoid using libstdc++ in this
+// case, which is covered by CR_USE_FALLBACKS_FOR_OLD_EXPERIMENTAL_GLIBCXX.
+// - When compiling libc++ from before r239653, with a gcc compiler, the
+// std::is_trivially_copyable can fail. So we need to work around that by not
+// using the one in libc++ in this case. This is covered by the
+// CR_USE_FALLBACKS_FOR_GCC_WITH_LIBCXX define, and is discussed in
+// https://llvm.org/bugs/show_bug.cgi?id=27538#c1 where they point out that
+// in libc++'s commit r239653 this is fixed by libc++ checking for gcc 5.1.
+// - In both of the above cases we are using the gcc compiler. When defining
+// this ourselves on compiler intrinsics, the __is_trivially_copyable()
+// intrinsic is not available on gcc before version 5.1 (see the discussion in
+// https://llvm.org/bugs/show_bug.cgi?id=27538#c1 again), so we must check for
+// that version.
+// - When __is_trivially_copyable() is not available because we are on gcc older
+// than 5.1, we need to fall back to something, so we use __has_trivial_copy()
+// instead based on what was done one-off in bit_cast() previously.
+
+// TODO(crbug.com/554293): Remove this when all platforms have this in the std
+// namespace and it works with gcc as needed.
+#if defined(CR_USE_FALLBACKS_FOR_OLD_GLIBCXX) || \
+ defined(CR_USE_FALLBACKS_FOR_OLD_EXPERIMENTAL_GLIBCXX) || \
+ defined(CR_USE_FALLBACKS_FOR_GCC_WITH_LIBCXX)
+template <typename T>
+struct is_trivially_copyable {
+// TODO(danakj): Remove this when android builders are all using a newer version
+// of gcc, or the android ndk is updated to a newer libc++ that does this for
+// us.
+#if _GNUC_VER >= 501
+ static constexpr bool value = __is_trivially_copyable(T);
+#else
+ static constexpr bool value = __has_trivial_copy(T);
+#endif
+};
+#else
+template <class T>
+using is_trivially_copyable = std::is_trivially_copyable<T>;
+#endif
+
+} // namespace base
+
+#undef CR_USE_FALLBACKS_FOR_OLD_GLIBCXX
+#undef CR_USE_FALLBACKS_FOR_GCC_WITH_LIBCXX
+#undef CR_USE_FALLBACKS_FOR_OLD_EXPERIMENTAL_GLIBCXX
+
+#endif // BASE_TEMPLATE_UTIL_H_