121 lines
3.7 KiB
C
121 lines
3.7 KiB
C
/* Copyright (C) 2012-2020 Free Software Foundation, Inc.
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Contributed by Richard Henderson <rth@redhat.com>.
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This file is part of the GNU Atomic Library (libatomic).
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Libatomic is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#include "libatomic_i.h"
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/* If we natively support the cas, and if we're unconcerned with extra
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barriers (e.g. fully in-order cpu for which barriers are a nop), then
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go ahead and expand the operation inline. */
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#if !defined(WANT_SPECIALCASE_RELAXED) && !defined(__OPTIMIZE_SIZE__)
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# define EXACT_INLINE(N) \
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if (C2(HAVE_ATOMIC_CAS_,N)) \
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return __atomic_compare_exchange_n \
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(PTR(N,mptr), PTR(N,eptr), *PTR(N,dptr), false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)
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#else
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# define EXACT_INLINE(N)
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#endif
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/* ... and if all that fails, invoke the function we generated elsewhere.
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Worst case, this will *also* use locks. */
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#define EXACT(N) \
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do { \
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if (!C2(HAVE_INT,N)) break; \
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if ((uintptr_t)mptr & (N - 1)) break; \
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EXACT_INLINE (N); \
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return C3(local_,compare_exchange_,N) \
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(PTR(N,mptr), PTR(N,eptr), *PTR(N,dptr), smodel, fmodel); \
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} while (0)
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#define LARGER(N) \
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do { \
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if (!C2(HAVE_INT,N)) break; \
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if (!C2(HAVE_ATOMIC_LDST_,N)) break; \
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if (!C2(MAYBE_HAVE_ATOMIC_CAS_,N)) break; \
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r = (uintptr_t)mptr & (N - 1); \
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a = (uintptr_t)mptr & -N; \
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if (r + n <= N) \
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{ \
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pre_barrier (smodel); \
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u.C2(i,N) = __atomic_load_n (PTR(N,a), __ATOMIC_RELAXED); \
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do { \
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if (memcmp (u.b + r, eptr, n) != 0) goto Lfail; \
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v = u; memcpy (v.b + r, dptr, n); \
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} while (!(C2(HAVE_ATOMIC_CAS_,N) \
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? __atomic_compare_exchange_n (PTR(N,a), \
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&u.C2(i,N), v.C2(i,N), true, \
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__ATOMIC_RELAXED, __ATOMIC_RELAXED) \
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: C3(local_,compare_exchange_,N) (PTR(N,a), \
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&u.C2(i,N), v.C2(i,N), \
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__ATOMIC_RELAXED, __ATOMIC_RELAXED))); \
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goto Lsucc; \
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} \
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} while (0)
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bool
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libat_compare_exchange (size_t n, void *mptr, void *eptr, void *dptr,
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int smodel, int fmodel)
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{
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union max_size_u u, v;
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uintptr_t r, a;
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bool ret;
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switch (n)
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{
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case 0: return true;
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case 1: EXACT(1); goto L4;
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case 2: EXACT(2); goto L4;
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case 4: EXACT(4); goto L8;
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case 8: EXACT(8); goto L16;
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case 16: EXACT(16); break;
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case 3: L4: LARGER(4); /* FALLTHRU */
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case 5 ... 7: L8: LARGER(8); /* FALLTHRU */
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case 9 ... 15: L16: LARGER(16); break;
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Lsucc:
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post_barrier (smodel);
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return true;
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Lfail:
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post_barrier (fmodel);
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memcpy (eptr, u.b + r, n);
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return false;
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}
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pre_seq_barrier (smodel);
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libat_lock_n (mptr, n);
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ret = memcmp (mptr, eptr, n) == 0;
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memcpy ((ret ? mptr : eptr), (ret ? dptr : mptr), n);
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libat_unlock_n (mptr, n);
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post_seq_barrier (ret ? smodel : fmodel);
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return ret;
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}
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EXPORT_ALIAS (compare_exchange);
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