libatomic/gexch.c

   1 /* Copyright (C) 2012-2023 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 exchange, 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_EXCHANGE_,N))                              \
  34     {                                                           \
  35       *PTR(N,rptr) = __atomic_exchange_n                        \
  36         (PTR(N,mptr), *PTR(N,vptr), __ATOMIC_SEQ_CST);          \
  37       return;                                                   \
  38     }
  39 #else
  40 # define EXACT_INLINE(N)
  41 #endif
  42
  43
  44 #define EXACT(N)                                                \
  45   do {                                                          \
  46     if (!C2(HAVE_INT,N)) break;                                 \
  47     if ((uintptr_t)mptr & (N - 1)) break;                       \
  48     EXACT_INLINE (N);                                           \
  49     *PTR(N,rptr) = C3(local_,exchange_,N)                       \
  50       (PTR(N,mptr), *PTR(N,vptr), smodel);                      \
  51     return;                                                     \
  52   } while (0)
  53
  54
  55 #define LARGER(N)                                               \
  56   do {                                                          \
  57     if (!C2(HAVE_INT,N)) break;                                 \
  58     if (!C2(MAYBE_HAVE_ATOMIC_CAS_,N)) break;                   \
  59     r = (uintptr_t)mptr & (N - 1);                              \
  60     a = (uintptr_t)mptr & -N;                                   \
  61     if (r + n <= N)                                             \
  62       {                                                         \
  63         pre_barrier (smodel);                                   \
  64         u.C2(i,N) = *PTR(N,a);                                  \
  65         do {                                                    \
  66           v = u;                                                \
  67           memcpy (v.b + r, vptr, n);                            \
  68         } while (!(C2(HAVE_ATOMIC_CAS_,N)                       \
  69                    ? __atomic_compare_exchange_n (PTR(N,a),     \
  70                         &u.C2(i,N), v.C2(i,N), true,            \
  71                         __ATOMIC_RELAXED, __ATOMIC_RELAXED)     \
  72                    : C3(local_,compare_exchange_,N) (PTR(N,a),  \
  73                         &u.C2(i,N), v.C2(i,N),                  \
  74                         __ATOMIC_RELAXED, __ATOMIC_RELAXED)));  \
  75         goto Lfinish;                                           \
  76       }                                                         \
  77   } while (0)
  78
  79
  80 static void __attribute__((noinline))
  81 libat_exchange_large_inplace (size_t n, void *mptr, void *vptr)
  82 {
  83 #define BUF     1024
  84
  85   char temp[BUF];
  86   size_t i = 0;
  87
  88   for (i = 0; n >= BUF; i += BUF, n -= BUF)
  89     {
  90       memcpy (temp, mptr + i, BUF);
  91       memcpy (mptr + i, vptr + i, BUF);
  92       memcpy (vptr + i, temp, BUF);
  93     }
  94   if (n > 0)
  95     {
  96       memcpy (temp, mptr + i, n);
  97       memcpy (mptr + i, vptr + i, n);
  98       memcpy (vptr + i, temp, n);
  99     }
 100
 101 #undef BUF
 102 }
 103
 104 void
 105 libat_exchange (size_t n, void *mptr, void *vptr, void *rptr, int smodel)
 106 {
 107   union max_size_u u, v;
 108   uintptr_t r, a;
 109
 110   switch (n)
 111     {
 112     case 0:                             return;
 113     case 1:             EXACT(1);       goto L4;
 114     case 2:             EXACT(2);       goto L4;
 115     case 4:             EXACT(4);       goto L8;
 116     case 8:             EXACT(8);       goto L16;
 117     case 16:            EXACT(16);      break;
 118
 119     case 3: L4:         LARGER(4);      /* FALLTHRU */
 120     case 5 ... 7: L8:   LARGER(8);      /* FALLTHRU */
 121     case 9 ... 15: L16: LARGER(16);     break;
 122
 123     Lfinish:
 124       post_barrier (smodel);
 125       memcpy (rptr, u.b + r, n);
 126       return;
 127     }
 128
 129   pre_seq_barrier (smodel);
 130   libat_lock_n (mptr, n);
 131
 132   if (vptr != rptr)
 133     {
 134       memcpy (rptr, mptr, n);
 135       memcpy (mptr, vptr, n);
 136     }
 137   else
 138     libat_exchange_large_inplace (n, mptr, vptr);
 139
 140   libat_unlock_n (mptr, n);
 141   post_seq_barrier (smodel);
 142 }
 143
 144 EXPORT_ALIAS (exchange);