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 && defined(atomic_compare_exchange_n) 30bool 31SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, 32 int smodel, int fmodel UNUSED) 33{ 34 if (maybe_specialcase_relaxed(smodel)) 35 return atomic_compare_exchange_n (mptr, eptr, newval, false, 36 __ATOMIC_RELAXED, __ATOMIC_RELAXED); 37 else if (maybe_specialcase_acqrel(smodel)) 38 return atomic_compare_exchange_n (mptr, eptr, newval, false, 39 __ATOMIC_ACQ_REL, __ATOMIC_RELAXED); 40 else 41 return atomic_compare_exchange_n (mptr, eptr, newval, false, 42 __ATOMIC_SEQ_CST, __ATOMIC_RELAXED); 43} 44 45#define DONE 1 46#endif /* HAVE_ATOMIC_CAS */ 47 48 49/* If this type is not larger than word-sized, fall back to a word-sized 50 compare-and-swap loop, possibly assisted by the OS. */ 51#if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w) 52bool 53SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, 54 int smodel, int fmodel) 55{ 56 UWORD mask, shift, weval, woldval, wnewval, t, *wptr; 57 58 pre_barrier (smodel); 59 60 if (N < WORDSIZE) 61 { 62 wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE); 63 shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK); 64 mask = SIZE(MASK) << shift; 65 } 66 else 67 { 68 wptr = (UWORD *)mptr; 69 shift = 0; 70 mask = -1; 71 } 72 73 weval = (UWORD)*eptr << shift; 74 wnewval = (UWORD)newval << shift; 75 woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED); 76 do 77 { 78 if ((woldval & mask) != weval) 79 goto failure; 80 t = (woldval & ~mask) | wnewval; 81 } 82 while (!atomic_compare_exchange_w (wptr, &woldval, t, true, 83 __ATOMIC_RELAXED, __ATOMIC_RELAXED)); 84 post_barrier (smodel); 85 return true; 86 87 failure: 88 *eptr = woldval >> shift; 89 post_barrier (fmodel); 90 return false; 91} 92 93#define DONE 1 94#endif /* HAVE_ATOMIC_CAS && N <= WORDSIZE */ 95 96 97/* Otherwise, fall back to some sort of protection mechanism. */ 98#if !DONE 99bool 100SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, 101 int smodel, int fmodel UNUSED) 102{ 103 UTYPE oldval; 104 UWORD magic; 105 bool ret; 106 107 pre_seq_barrier (smodel); 108 magic = protect_start (mptr); 109 110 oldval = *mptr; 111 ret = (oldval == *eptr); 112 if (ret) 113 *mptr = newval; 114 else 115 *eptr = oldval; 116 117 protect_end (mptr, magic); 118 post_seq_barrier (smodel); 119 120 return ret; 121} 122#endif 123 124EXPORT_ALIAS (SIZE(compare_exchange)); 125