1/* Copyright (C) 2012-2015 Free Software Foundation, Inc. 2 Contributed by Richard Henderson <rth@redhat.com>. 3 4 This file is part of the GNU Atomic Library (libatomic). 5 6 Libatomic is free software; you can redistribute it and/or modify it 7 under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 3 of the License, or 9 (at your option) any later version. 10 11 Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY 12 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 13 FOR A PARTICULAR PURPOSE. See the GNU General Public License for 14 more details. 15 16 Under Section 7 of GPL version 3, you are granted additional 17 permissions described in the GCC Runtime Library Exception, version 18 3.1, as published by the Free Software Foundation. 19 20 You should have received a copy of the GNU General Public License and 21 a copy of the GCC Runtime Library Exception along with this program; 22 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23 <http://www.gnu.org/licenses/>. */ 24 25#include "libatomic_i.h" 26 27 28/* If we natively support the cas, and if we're unconcerned with extra 29 barriers (e.g. fully in-order cpu for which barriers are a nop), then 30 go ahead and expand the operation inline. */ 31#if !defined(WANT_SPECIALCASE_RELAXED) && !defined(__OPTIMIZE_SIZE__) 32# define EXACT_INLINE(N) \ 33 if (C2(HAVE_ATOMIC_CAS_,N)) \ 34 return __atomic_compare_exchange_n \ 35 (PTR(N,mptr), PTR(N,eptr), *PTR(N,dptr), false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) 36#else 37# define EXACT_INLINE(N) 38#endif 39 40/* ... and if all that fails, invoke the function we generated elsewhere. 41 Worst case, this will *also* use locks. */ 42#define EXACT(N) \ 43 do { \ 44 if (!C2(HAVE_INT,N)) break; \ 45 if ((uintptr_t)mptr & (N - 1)) break; \ 46 EXACT_INLINE (N); \ 47 return C3(local_,compare_exchange_,N) \ 48 (PTR(N,mptr), PTR(N,eptr), *PTR(N,dptr), smodel, fmodel); \ 49 } while (0) 50 51#define LARGER(N) \ 52 do { \ 53 if (!C2(HAVE_INT,N)) break; \ 54 if (!C2(HAVE_ATOMIC_LDST_,N)) break; \ 55 if (!C2(MAYBE_HAVE_ATOMIC_CAS_,N)) break; \ 56 r = (uintptr_t)mptr & (N - 1); \ 57 a = (uintptr_t)mptr & -N; \ 58 if (r + n <= N) \ 59 { \ 60 pre_barrier (smodel); \ 61 u.C2(i,N) = __atomic_load_n (PTR(N,a), __ATOMIC_RELAXED); \ 62 do { \ 63 if (memcmp (u.b + r, eptr, n) != 0) goto Lfail; \ 64 v = u; memcpy (v.b + r, dptr, n); \ 65 } while (!(C2(HAVE_ATOMIC_CAS_,N) \ 66 ? __atomic_compare_exchange_n (PTR(N,a), \ 67 &u.C2(i,N), v.C2(i,N), true, \ 68 __ATOMIC_RELAXED, __ATOMIC_RELAXED) \ 69 : C3(local_,compare_exchange_,N) (PTR(N,a), \ 70 &u.C2(i,N), v.C2(i,N), \ 71 __ATOMIC_RELAXED, __ATOMIC_RELAXED))); \ 72 goto Lsucc; \ 73 } \ 74 } while (0) 75 76 77 78bool 79libat_compare_exchange (size_t n, void *mptr, void *eptr, void *dptr, 80 int smodel, int fmodel) 81{ 82 union max_size_u u, v; 83 uintptr_t r, a; 84 bool ret; 85 86 switch (n) 87 { 88 case 0: return true; 89 case 1: EXACT(1); goto L4; 90 case 2: EXACT(2); goto L4; 91 case 4: EXACT(4); goto L8; 92 case 8: EXACT(8); goto L16; 93 case 16: EXACT(16); break; 94 95 case 3: L4: LARGER(4); /* FALLTHRU */ 96 case 5 ... 7: L8: LARGER(8); /* FALLTHRU */ 97 case 9 ... 15: L16: LARGER(16); break; 98 99 Lsucc: 100 post_barrier (smodel); 101 return true; 102 Lfail: 103 post_barrier (fmodel); 104 memcpy (eptr, u.b + r, n); 105 return false; 106 } 107 108 pre_seq_barrier (smodel); 109 libat_lock_n (mptr, n); 110 111 ret = memcmp (mptr, eptr, n) == 0; 112 memcpy ((ret ? mptr : eptr), (ret ? dptr : mptr), n); 113 114 libat_unlock_n (mptr, n); 115 post_seq_barrier (ret ? smodel : fmodel); 116 117 return ret; 118} 119 120EXPORT_ALIAS (compare_exchange); 121