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