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1 /* Copyright (C) 2012-2018 Free Software Foundation, Inc.
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2 Contributed by Richard Henderson <rth@redhat.com>.
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3
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4 This file is part of the GNU Atomic Library (libatomic).
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5
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6 Libatomic is free software; you can redistribute it and/or modify it
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7 under the terms of the GNU General Public License as published by
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8 the Free Software Foundation; either version 3 of the License, or
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9 (at your option) any later version.
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10
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11 Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
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12 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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13 FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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14 more details.
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15
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16 Under Section 7 of GPL version 3, you are granted additional
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17 permissions described in the GCC Runtime Library Exception, version
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18 3.1, as published by the Free Software Foundation.
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19
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20 You should have received a copy of the GNU General Public License and
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21 a copy of the GCC Runtime Library Exception along with this program;
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22 see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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23 <http://www.gnu.org/licenses/>. */
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24
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25 #include "libatomic_i.h"
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26
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27
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28 /* If we support the builtin, just use it. */
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29 #if !DONE && SIZE(HAVE_ATOMIC_EXCHANGE)
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30 UTYPE
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31 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
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32 {
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33 if (maybe_specialcase_relaxed(smodel))
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34 return __atomic_exchange_n (mptr, newval, __ATOMIC_RELAXED);
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35 else if (maybe_specialcase_acqrel(smodel))
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36 return __atomic_exchange_n (mptr, newval, __ATOMIC_ACQ_REL);
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37 else
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38 return __atomic_exchange_n (mptr, newval, __ATOMIC_SEQ_CST);
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39 }
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40
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41 #define DONE 1
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42 #endif /* HAVE_ATOMIC_EXCHANGE */
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43
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44
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45 #if !DONE && defined(atomic_compare_exchange_n)
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46 UTYPE
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47 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
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48 {
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49 UTYPE oldval;
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50
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51 pre_barrier (smodel);
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52
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53 oldval = *mptr;
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54 while (!atomic_compare_exchange_n (mptr, &oldval, newval, true,
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55 __ATOMIC_RELAXED, __ATOMIC_RELAXED))
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56 continue;
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57
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58 post_barrier (smodel);
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59
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60 return oldval;
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61 }
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62
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63 #define DONE 1
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64 #endif /* atomic_compare_exchange_n */
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65
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66
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67 /* If this type is smaller than word-sized, fall back to a word-sized
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68 compare-and-swap loop. */
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69 #if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w)
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70 UTYPE
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71 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
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72 {
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73 UWORD mask, shift, woldval, wnewval, t, *wptr;
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74
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75 pre_barrier (smodel);
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76
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77 if (N < WORDSIZE)
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78 {
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79 wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
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80 shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
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81 mask = SIZE(MASK) << shift;
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82 }
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83 else
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84 {
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85 wptr = (UWORD *)mptr;
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86 shift = 0;
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87 mask = -1;
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88 }
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89
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90 wnewval = (UWORD)newval << shift;
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91 woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
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92 do
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93 {
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94 t = (woldval & ~mask) | wnewval;
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95 }
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96 while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
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97 __ATOMIC_RELAXED, __ATOMIC_RELAXED));
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98
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99 post_barrier (smodel);
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100 return woldval >> shift;
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101 }
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102
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103 #define DONE 1
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104 #endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */
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105
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106
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107 /* Otherwise, fall back to some sort of protection mechanism. */
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108 #if !DONE
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109 UTYPE
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110 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel UNUSED)
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111 {
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112 UTYPE oldval;
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113 UWORD magic;
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114
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115 pre_seq_barrier (smodel);
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116 magic = protect_start (mptr);
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117
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118 oldval = *mptr;
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119 *mptr = newval;
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120
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121 protect_end (mptr, magic);
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122 post_seq_barrier (smodel);
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123
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124 return oldval;
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125 }
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126 #endif
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127
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128 EXPORT_ALIAS (SIZE(exchange));
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