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133 lines
4.5 KiB
C++
133 lines
4.5 KiB
C++
#ifndef RBIMPL_STDALIGN_H /*-*-C++-*-vi:se ft=cpp:*/
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#define RBIMPL_STDALIGN_H
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/**
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* @file
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* @author Ruby developers <ruby-core@ruby-lang.org>
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* @copyright This file is a part of the programming language Ruby.
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* Permission is hereby granted, to either redistribute and/or
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* modify this file, provided that the conditions mentioned in the
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* file COPYING are met. Consult the file for details.
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* @warning Symbols prefixed with either `RBIMPL` or `rbimpl` are
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* implementation details. Don't take them as canon. They could
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* rapidly appear then vanish. The name (path) of this header file
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* is also an implementation detail. Do not expect it to persist
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* at the place it is now. Developers are free to move it anywhere
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* anytime at will.
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* @note To ruby-core: remember that this header can be possibly
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* recursively included from extension libraries written in C++.
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* Do not expect for instance `__VA_ARGS__` is always available.
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* We assume C99 for ruby itself but we don't assume languages of
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* extension libraries. They could be written in C++98.
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* @brief Defines #RBIMPL_ALIGNAS / #RBIMPL_ALIGNOF
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*/
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#include "ruby/internal/config.h"
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#ifdef STDC_HEADERS
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# include <stddef.h>
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#endif
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#include "ruby/internal/compiler_is.h"
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#include "ruby/internal/has/attribute.h"
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#include "ruby/internal/has/declspec_attribute.h"
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#include "ruby/internal/has/feature.h"
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/**
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* Wraps (or simulates) `alignas`. This is C++11's `alignas` and is _different_
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* from C11 `_Alignas`. For instance,
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*
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* ```CXX
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* typedef struct alignas(128) foo { int foo } foo;
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* ```
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*
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* is a valid C++ while
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*
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* ```C
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* typedef struct _Alignas(128) foo { int foo } foo;
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* ```
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*
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* is an invalid C because:
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*
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* - You cannot `struct _Alignas`.
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* - A `typedef` cannot have alignments.
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*/
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#if defined(__cplusplus) && RBIMPL_HAS_FEATURE(cxx_alignas)
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# define RBIMPL_ALIGNAS alignas
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#elif defined(__cplusplus) && (__cplusplus >= 201103L)
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# define RBIMPL_ALIGNAS alignas
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#elif defined(__INTEL_CXX11_MODE__)
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# define RBIMPL_ALIGNAS alignas
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#elif defined(__GXX_EXPERIMENTAL_CXX0X__)
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# define RBIMPL_ALIGNAS alignas
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#elif RBIMPL_HAS_DECLSPEC_ATTRIBUTE(align)
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# define RBIMPL_ALIGNAS(_) __declspec(align(_))
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#elif RBIMPL_HAS_ATTRIBUTE(aligned)
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# define RBIMPL_ALIGNAS(_) __attribute__((__aligned__(_)))
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#else
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# define RBIMPL_ALIGNAS(_) /* void */
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#endif
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/**
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* Wraps (or simulates) `alignof`.
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*
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* We want C11's `_Alignof`. However in spite of its clear language, compilers
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* (including GCC and clang) tend to have buggy implementations. We have to
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* avoid such things to resort to our own version.
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*
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* @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023
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* @see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560
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* @see https://bugs.llvm.org/show_bug.cgi?id=26547
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*/
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#if defined(__cplusplus)
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# /* C++11 `alignof()` can be buggy. */
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# /* see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69560 */
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# /* But don't worry, we can use templates. */
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# define RBIMPL_ALIGNOF(T) (static_cast<size_t>(ruby::rbimpl_alignof<T>::value))
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namespace ruby {
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template<typename T>
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struct rbimpl_alignof {
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typedef struct {
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char _;
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T t;
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} type;
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enum {
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value = offsetof(type, t)
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};
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};
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}
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#elif RBIMPL_COMPILER_IS(MSVC)
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# /* Windows have no alignment glitch.*/
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# define RBIMPL_ALIGNOF __alignof
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#elif defined(HAVE__ALIGNOF)
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# /* Autoconf detected availability of a sane `_Alignof()`. */
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# define RBIMPL_ALIGNOF(T) RB_GNUC_EXTENSION(_Alignof(T))
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#else
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# /* :BEWARE: This is the last resort. If your compiler somehow supports
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# * querying the alignment of a type, you definitely should use that instead.
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# * There are 2 known pitfalls for this fallback implementation:
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# *
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# * First, it is either an undefined behaviour (C) or an explicit error (C++)
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# * to define a struct inside of `offsetof`. C compilers tend to accept such
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# * things, but AFAIK C++ has no room to allow.
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# *
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# * Second, there exist T such that `struct { char _; T t; }` is invalid. A
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# * known example is when T is a struct with a flexible array member. Such
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# * struct cannot be enclosed into another one.
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# */
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# /* see: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2083.htm */
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# /* see: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm */
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# define RBIMPL_ALIGNOF(T) offsetof(struct { char _; T t; }, t)
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#endif
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#endif /* RBIMPL_STDALIGN_H */
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