| /* Copyright (C) 2012-2018 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); |