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7adcbafe | 1 | /* Copyright (C) 2012-2022 Free Software Foundation, Inc. |
48310492 RH |
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 \ | |
94f3ccc8 | 35 | (PTR(N,mptr), PTR(N,eptr), *PTR(N,dptr), false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) |
48310492 RH |
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 | ||
78 | bool | |
79 | libat_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 | ||
120 | EXPORT_ALIAS (compare_exchange); |