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8d9254fc | 1 | /* Copyright (C) 2012-2020 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 support the builtin, just use it. */ | |
29 | #if !DONE && defined(atomic_compare_exchange_n) | |
30 | bool | |
31 | SIZE(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) | |
52 | bool | |
53 | SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, | |
672ce939 | 54 | int smodel, int fmodel) |
48310492 RH |
55 | { |
56 | UWORD mask, shift, weval, woldval, wnewval, t, *wptr; | |
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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 | ||
ca3d99a6 | 73 | weval = (UWORD)*eptr << shift; |
48310492 RH |
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)); | |
672ce939 RH |
84 | post_barrier (smodel); |
85 | return true; | |
86 | ||
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87 | failure: |
88 | *eptr = woldval >> shift; | |
672ce939 RH |
89 | post_barrier (fmodel); |
90 | return false; | |
48310492 RH |
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 | |
99 | bool | |
100 | SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, | |
101 | int smodel, int fmodel UNUSED) | |
102 | { | |
103 | UTYPE oldval; | |
104 | UWORD magic; | |
672ce939 | 105 | bool ret; |
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106 | |
107 | pre_seq_barrier (smodel); | |
108 | magic = protect_start (mptr); | |
109 | ||
110 | oldval = *mptr; | |
672ce939 RH |
111 | ret = (oldval == *eptr); |
112 | if (ret) | |
113 | *mptr = newval; | |
114 | else | |
115 | *eptr = oldval; | |
48310492 RH |
116 | |
117 | protect_end (mptr, magic); | |
118 | post_seq_barrier (smodel); | |
119 | ||
120 | return ret; | |
121 | } | |
122 | #endif | |
123 | ||
124 | EXPORT_ALIAS (SIZE(compare_exchange)); |