/* Copyright (C) 2012-2016 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);