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