libatomic/exch_n.c

   1 /* Copyright (C) 2012-2024 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 #define LAT_EXCH_N
  26 #include "libatomic_i.h"
  27
  28
  29 /* If we support the builtin, just use it.  */
  30 #if !DONE && SIZE(HAVE_ATOMIC_EXCHANGE)
  31 UTYPE
  32 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
  33 {
  34   if (maybe_specialcase_relaxed(smodel))
  35     return __atomic_exchange_n (mptr, newval, __ATOMIC_RELAXED);
  36   else if (maybe_specialcase_acqrel(smodel))
  37     return __atomic_exchange_n (mptr, newval, __ATOMIC_ACQ_REL);
  38   else
  39     return __atomic_exchange_n (mptr, newval, __ATOMIC_SEQ_CST);
  40 }
  41
  42 #define DONE 1
  43 #endif /* HAVE_ATOMIC_EXCHANGE */
  44
  45
  46 #if !DONE && defined(atomic_compare_exchange_n)
  47 UTYPE
  48 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
  49 {
  50   UTYPE oldval;
  51
  52   pre_barrier (smodel);
  53
  54   oldval = *mptr;
  55   while (!atomic_compare_exchange_n (mptr, &oldval, newval, true,
  56                                      __ATOMIC_RELAXED, __ATOMIC_RELAXED))
  57     continue;
  58
  59   post_barrier (smodel);
  60
  61   return oldval;
  62 }
  63
  64 #define DONE 1
  65 #endif /* atomic_compare_exchange_n */
  66
  67
  68 /* If this type is smaller than word-sized, fall back to a word-sized
  69    compare-and-swap loop.  */
  70 #if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w)
  71 UTYPE
  72 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
  73 {
  74   UWORD mask, shift, woldval, wnewval, t, *wptr;
  75
  76   pre_barrier (smodel);
  77
  78   if (N < WORDSIZE)
  79     {
  80       wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
  81       shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
  82       mask = SIZE(MASK) << shift;
  83     }
  84   else
  85     {
  86       wptr = (UWORD *)mptr;
  87       shift = 0;
  88       mask = -1;
  89     }
  90
  91   wnewval = (UWORD)newval << shift;
  92   woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
  93   do
  94     {
  95       t = (woldval & ~mask) | wnewval;
  96     }
  97   while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
  98                                      __ATOMIC_RELAXED, __ATOMIC_RELAXED));
  99
 100   post_barrier (smodel);
 101   return woldval >> shift;
 102 }
 103
 104 #define DONE 1
 105 #endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */
 106
 107
 108 /* Otherwise, fall back to some sort of protection mechanism.  */
 109 #if !DONE
 110 UTYPE
 111 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel UNUSED)
 112 {
 113   UTYPE oldval;
 114   UWORD magic;
 115
 116   pre_seq_barrier (smodel);
 117   magic = protect_start (mptr);
 118
 119   oldval = *mptr;
 120   *mptr = newval;
 121
 122   protect_end (mptr, magic);
 123   post_seq_barrier (smodel);
 124
 125   return oldval;
 126 }
 127 #endif
 128
 129 EXPORT_ALIAS (SIZE(exchange));
 130 #undef LAT_EXCH_N