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1 /* Copyright (C) 2012-2020 Free Software Foundation, Inc.
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111
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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 natively support the cas, and if we're unconcerned with extra
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29 barriers (e.g. fully in-order cpu for which barriers are a nop), then
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30 go ahead and expand the operation inline. */
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31 #if !defined(WANT_SPECIALCASE_RELAXED) && !defined(__OPTIMIZE_SIZE__)
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32 # define EXACT_INLINE(N) \
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33 if (C2(HAVE_ATOMIC_CAS_,N)) \
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34 return __atomic_compare_exchange_n \
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35 (PTR(N,mptr), PTR(N,eptr), *PTR(N,dptr), false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)
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36 #else
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37 # define EXACT_INLINE(N)
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38 #endif
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39
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40 /* ... and if all that fails, invoke the function we generated elsewhere.
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41 Worst case, this will *also* use locks. */
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42 #define EXACT(N) \
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43 do { \
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44 if (!C2(HAVE_INT,N)) break; \
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45 if ((uintptr_t)mptr & (N - 1)) break; \
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46 EXACT_INLINE (N); \
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47 return C3(local_,compare_exchange_,N) \
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48 (PTR(N,mptr), PTR(N,eptr), *PTR(N,dptr), smodel, fmodel); \
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49 } while (0)
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50
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51 #define LARGER(N) \
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52 do { \
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53 if (!C2(HAVE_INT,N)) break; \
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54 if (!C2(HAVE_ATOMIC_LDST_,N)) break; \
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55 if (!C2(MAYBE_HAVE_ATOMIC_CAS_,N)) break; \
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56 r = (uintptr_t)mptr & (N - 1); \
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57 a = (uintptr_t)mptr & -N; \
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58 if (r + n <= N) \
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59 { \
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60 pre_barrier (smodel); \
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61 u.C2(i,N) = __atomic_load_n (PTR(N,a), __ATOMIC_RELAXED); \
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62 do { \
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63 if (memcmp (u.b + r, eptr, n) != 0) goto Lfail; \
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64 v = u; memcpy (v.b + r, dptr, n); \
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65 } while (!(C2(HAVE_ATOMIC_CAS_,N) \
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66 ? __atomic_compare_exchange_n (PTR(N,a), \
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67 &u.C2(i,N), v.C2(i,N), true, \
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68 __ATOMIC_RELAXED, __ATOMIC_RELAXED) \
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69 : C3(local_,compare_exchange_,N) (PTR(N,a), \
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70 &u.C2(i,N), v.C2(i,N), \
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71 __ATOMIC_RELAXED, __ATOMIC_RELAXED))); \
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72 goto Lsucc; \
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73 } \
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74 } while (0)
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75
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76
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77
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78 bool
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79 libat_compare_exchange (size_t n, void *mptr, void *eptr, void *dptr,
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80 int smodel, int fmodel)
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81 {
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82 union max_size_u u, v;
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83 uintptr_t r, a;
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84 bool ret;
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85
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86 switch (n)
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87 {
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88 case 0: return true;
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89 case 1: EXACT(1); goto L4;
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90 case 2: EXACT(2); goto L4;
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91 case 4: EXACT(4); goto L8;
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92 case 8: EXACT(8); goto L16;
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93 case 16: EXACT(16); break;
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94
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95 case 3: L4: LARGER(4); /* FALLTHRU */
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96 case 5 ... 7: L8: LARGER(8); /* FALLTHRU */
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97 case 9 ... 15: L16: LARGER(16); break;
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98
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99 Lsucc:
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100 post_barrier (smodel);
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101 return true;
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102 Lfail:
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103 post_barrier (fmodel);
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104 memcpy (eptr, u.b + r, n);
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105 return false;
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106 }
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107
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108 pre_seq_barrier (smodel);
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109 libat_lock_n (mptr, n);
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110
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111 ret = memcmp (mptr, eptr, n) == 0;
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112 memcpy ((ret ? mptr : eptr), (ret ? dptr : mptr), n);
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113
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114 libat_unlock_n (mptr, n);
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115 post_seq_barrier (ret ? smodel : fmodel);
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116
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117 return ret;
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118 }
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119
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120 EXPORT_ALIAS (compare_exchange);
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