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/* Copyright (C) 2012-2022 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 natively support the cas, and if we're unconcerned with extra
barriers (e.g. fully in-order cpu for which barriers are a nop), then
go ahead and expand the operation inline. */
#if !defined(WANT_SPECIALCASE_RELAXED) && !defined(__OPTIMIZE_SIZE__)
# define EXACT_INLINE(N) \
if (C2(HAVE_ATOMIC_CAS_,N)) \
return __atomic_compare_exchange_n \
(PTR(N,mptr), PTR(N,eptr), *PTR(N,dptr), false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)
#else
# define EXACT_INLINE(N)
#endif
/* ... and if all that fails, invoke the function we generated elsewhere.
Worst case, this will *also* use locks. */
#define EXACT(N) \
do { \
if (!C2(HAVE_INT,N)) break; \
if ((uintptr_t)mptr & (N - 1)) break; \
EXACT_INLINE (N); \
return C3(local_,compare_exchange_,N) \
(PTR(N,mptr), PTR(N,eptr), *PTR(N,dptr), smodel, fmodel); \
} while (0)
#define LARGER(N) \
do { \
if (!C2(HAVE_INT,N)) break; \
if (!C2(HAVE_ATOMIC_LDST_,N)) break; \
if (!C2(MAYBE_HAVE_ATOMIC_CAS_,N)) break; \
r = (uintptr_t)mptr & (N - 1); \
a = (uintptr_t)mptr & -N; \
if (r + n <= N) \
{ \
pre_barrier (smodel); \
u.C2(i,N) = __atomic_load_n (PTR(N,a), __ATOMIC_RELAXED); \
do { \
if (memcmp (u.b + r, eptr, n) != 0) goto Lfail; \
v = u; memcpy (v.b + r, dptr, n); \
} while (!(C2(HAVE_ATOMIC_CAS_,N) \
? __atomic_compare_exchange_n (PTR(N,a), \
&u.C2(i,N), v.C2(i,N), true, \
__ATOMIC_RELAXED, __ATOMIC_RELAXED) \
: C3(local_,compare_exchange_,N) (PTR(N,a), \
&u.C2(i,N), v.C2(i,N), \
__ATOMIC_RELAXED, __ATOMIC_RELAXED))); \
goto Lsucc; \
} \
} while (0)
bool
libat_compare_exchange (size_t n, void *mptr, void *eptr, void *dptr,
int smodel, int fmodel)
{
union max_size_u u, v;
uintptr_t r, a;
bool ret;
switch (n)
{
case 0: return true;
case 1: EXACT(1); goto L4;
case 2: EXACT(2); goto L4;
case 4: EXACT(4); goto L8;
case 8: EXACT(8); goto L16;
case 16: EXACT(16); break;
case 3: L4: LARGER(4); /* FALLTHRU */
case 5 ... 7: L8: LARGER(8); /* FALLTHRU */
case 9 ... 15: L16: LARGER(16); break;
Lsucc:
post_barrier (smodel);
return true;
Lfail:
post_barrier (fmodel);
memcpy (eptr, u.b + r, n);
return false;
}
pre_seq_barrier (smodel);
libat_lock_n (mptr, n);
ret = memcmp (mptr, eptr, n) == 0;
memcpy ((ret ? mptr : eptr), (ret ? dptr : mptr), n);
libat_unlock_n (mptr, n);
post_seq_barrier (ret ? smodel : fmodel);
return ret;
}
EXPORT_ALIAS (compare_exchange);
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