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 support the builtin, just use it. */ 29#if !DONE && SIZE(HAVE_ATOMIC_EXCHANGE) 30UTYPE 31SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel) 32{ 33 if (maybe_specialcase_relaxed(smodel)) 34 return __atomic_exchange_n (mptr, newval, __ATOMIC_RELAXED); 35 else if (maybe_specialcase_acqrel(smodel)) 36 return __atomic_exchange_n (mptr, newval, __ATOMIC_ACQ_REL); 37 else 38 return __atomic_exchange_n (mptr, newval, __ATOMIC_SEQ_CST); 39} 40 41#define DONE 1 42#endif /* HAVE_ATOMIC_EXCHANGE */ 43 44 45#if !DONE && defined(atomic_compare_exchange_n) 46UTYPE 47SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel) 48{ 49 UTYPE oldval; 50 51 pre_barrier (smodel); 52 53 oldval = *mptr; 54 while (!atomic_compare_exchange_n (mptr, &oldval, newval, true, 55 __ATOMIC_RELAXED, __ATOMIC_RELAXED)) 56 continue; 57 58 post_barrier (smodel); 59 60 return oldval; 61} 62 63#define DONE 1 64#endif /* atomic_compare_exchange_n */ 65 66 67/* If this type is smaller than word-sized, fall back to a word-sized 68 compare-and-swap loop. */ 69#if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w) 70UTYPE 71SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel) 72{ 73 UWORD mask, shift, woldval, wnewval, t, *wptr; 74 75 pre_barrier (smodel); 76 77 if (N < WORDSIZE) 78 { 79 wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE); 80 shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK); 81 mask = SIZE(MASK) << shift; 82 } 83 else 84 { 85 wptr = (UWORD *)mptr; 86 shift = 0; 87 mask = -1; 88 } 89 90 wnewval = (UWORD)newval << shift; 91 woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED); 92 do 93 { 94 t = (woldval & ~mask) | wnewval; 95 } 96 while (!atomic_compare_exchange_w (wptr, &woldval, t, true, 97 __ATOMIC_RELAXED, __ATOMIC_RELAXED)); 98 99 post_barrier (smodel); 100 return woldval >> shift; 101} 102 103#define DONE 1 104#endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */ 105 106 107/* Otherwise, fall back to some sort of protection mechanism. */ 108#if !DONE 109UTYPE 110SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel UNUSED) 111{ 112 UTYPE oldval; 113 UWORD magic; 114 115 pre_seq_barrier (smodel); 116 magic = protect_start (mptr); 117 118 oldval = *mptr; 119 *mptr = newval; 120 121 protect_end (mptr, magic); 122 post_seq_barrier (smodel); 123 124 return oldval; 125} 126#endif 127 128EXPORT_ALIAS (SIZE(exchange)); 129