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/* Copyright (C) 2022 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef PACKED_H
#define PACKED_H
/* Each instantiation and full specialization of the packed template
defines a type that behaves like a given scalar type, but that has
byte alignment, and, may optionally have a smaller size than the
given scalar type. This is typically used as alternative to
bit-fields (and ENUM_BITFIELD), when the fields must have separate
memory locations to avoid data races. */
template<typename T, size_t Bytes = sizeof (T)>
struct packed
{
public:
packed (T val)
{
m_val = val;
/* Ensure size and aligment are what we expect. */
gdb_static_assert (sizeof (packed) == Bytes);
gdb_static_assert (alignof (packed) == 1);
/* Make sure packed can be wrapped with std::atomic. */
gdb_static_assert (std::is_trivially_copyable<packed>::value);
gdb_static_assert (std::is_copy_constructible<packed>::value);
gdb_static_assert (std::is_move_constructible<packed>::value);
gdb_static_assert (std::is_copy_assignable<packed>::value);
gdb_static_assert (std::is_move_assignable<packed>::value);
}
operator T () const noexcept
{
return m_val;
}
private:
T m_val : (Bytes * HOST_CHAR_BIT) ATTRIBUTE_PACKED;
};
/* Add some comparisons between std::atomic<packed<T>> and T. We need
this because the regular comparisons would require two implicit
conversions to go from T to std::atomic<packed<T>>:
T -> packed<T>
packed<T> -> std::atomic<packed<T>>
and C++ only does one. */
template<typename T, size_t Bytes>
bool operator== (T lhs, const std::atomic<packed<T, Bytes>> &rhs)
{
return lhs == rhs.load ();
}
template<typename T, size_t Bytes>
bool operator== (const std::atomic<packed<T, Bytes>> &lhs, T rhs)
{
return lhs.load () == rhs;
}
template<typename T, size_t Bytes>
bool operator!= (T lhs, const std::atomic<packed<T, Bytes>> &rhs)
{
return !(lhs == rhs);
}
template<typename T, size_t Bytes>
bool operator!= (const std::atomic<packed<T, Bytes>> &lhs, T rhs)
{
return !(lhs == rhs);
}
#endif
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