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/* Copyright (C) 2012-2021 Free Software Foundation, Inc.
Contributed by Richard Henderson <rth@redhat.com>.
This file is part of the GNU Atomic Library (libatomic).
Libatomic 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.
Libatomic 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.
Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.
You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
<http://www.gnu.org/licenses/>. */
#include "libatomic_i.h"
/* If we support the builtin, just use it. */
#if !DONE && SIZE(HAVE_ATOMIC_LDST)
UTYPE
SIZE(libat_load) (UTYPE *mptr, int smodel)
{
if (maybe_specialcase_relaxed(smodel))
return __atomic_load_n (mptr, __ATOMIC_RELAXED);
else if (maybe_specialcase_acqrel(smodel))
/* Note that REL and ACQ_REL are not valid for loads. */
return __atomic_load_n (mptr, __ATOMIC_ACQUIRE);
else
return __atomic_load_n (mptr, __ATOMIC_SEQ_CST);
}
#define DONE 1
#endif /* HAVE_ATOMIC_LOAD */
/* If we have compare-and-swap, use it to swap 0 with 0 and as a side
effect load the original value. */
#if !DONE && defined(atomic_compare_exchange_n)
UTYPE
SIZE(libat_load) (UTYPE *mptr, int smodel)
{
UTYPE t = 0;
if (maybe_specialcase_relaxed(smodel))
atomic_compare_exchange_n (mptr, &t, 0, true,
__ATOMIC_RELAXED, __ATOMIC_RELAXED);
else if (maybe_specialcase_acqrel(smodel))
atomic_compare_exchange_n (mptr, &t, 0, true,
__ATOMIC_ACQ_REL, __ATOMIC_ACQ_REL);
else
atomic_compare_exchange_n (mptr, &t, 0, true,
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
return t;
}
#define DONE 1
#endif /* atomic_compare_exchange_n */
/* Similar, but only assume a word-sized compare-and-swap. */
#if !DONE && N < WORDSIZE && defined(atomic_compare_exchange_w)
UTYPE
SIZE(libat_load) (UTYPE *mptr, int smodel)
{
UWORD shift, t, *wptr;
pre_barrier (smodel);
wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
/* Exchange 0 with 0, placing the old value of *WPTR in T. */
t = 0;
atomic_compare_exchange_w (wptr, &t, 0);
post_barrier (smodel);
return t >> shift;
}
#define DONE 1
#endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */
/* Otherwise, fall back to some sort of protection mechanism. */
#if !DONE
UTYPE
SIZE(libat_load) (UTYPE *mptr, int smodel)
{
UTYPE ret;
UWORD magic;
pre_seq_barrier (smodel);
magic = protect_start (mptr);
ret = *mptr;
protect_end (mptr, magic);
post_seq_barrier (smodel);
return ret;
}
#endif
EXPORT_ALIAS (SIZE(load));
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