libatomic/exch_n.c

   1 /* Copyright (C) 2012-2021 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 support the builtin, just use it.  */
  29 #if !DONE && SIZE(HAVE_ATOMIC_EXCHANGE)
  30 UTYPE
  31 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
  32 {
  33   if (maybe_specialcase_relaxed(smodel))
  34     return __atomic_exchange_n (mptr, newval, __ATOMIC_RELAXED);
  35   else if (maybe_specialcase_acqrel(smodel))
  36     return __atomic_exchange_n (mptr, newval, __ATOMIC_ACQ_REL);
  37   else
  38     return __atomic_exchange_n (mptr, newval, __ATOMIC_SEQ_CST);
  39 }
  40
  41 #define DONE 1
  42 #endif /* HAVE_ATOMIC_EXCHANGE */
  43
  44
  45 #if !DONE && defined(atomic_compare_exchange_n)
  46 UTYPE
  47 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
  48 {
  49   UTYPE oldval;
  50
  51   pre_barrier (smodel);
  52
  53   oldval = *mptr;
  54   while (!atomic_compare_exchange_n (mptr, &oldval, newval, true,
  55                                      __ATOMIC_RELAXED, __ATOMIC_RELAXED))
  56     continue;
  57
  58   post_barrier (smodel);
  59
  60   return oldval;
  61 }
  62
  63 #define DONE 1
  64 #endif /* atomic_compare_exchange_n */
  65
  66
  67 /* If this type is smaller than word-sized, fall back to a word-sized
  68    compare-and-swap loop.  */
  69 #if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w)
  70 UTYPE
  71 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel)
  72 {
  73   UWORD mask, shift, woldval, wnewval, t, *wptr;
  74
  75   pre_barrier (smodel);
  76
  77   if (N < WORDSIZE)
  78     {
  79       wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
  80       shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
  81       mask = SIZE(MASK) << shift;
  82     }
  83   else
  84     {
  85       wptr = (UWORD *)mptr;
  86       shift = 0;
  87       mask = -1;
  88     }
  89
  90   wnewval = (UWORD)newval << shift;
  91   woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
  92   do
  93     {
  94       t = (woldval & ~mask) | wnewval;
  95     }
  96   while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
  97                                      __ATOMIC_RELAXED, __ATOMIC_RELAXED));
  98
  99   post_barrier (smodel);
 100   return woldval >> shift;
 101 }
 102
 103 #define DONE 1
 104 #endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */
 105
 106
 107 /* Otherwise, fall back to some sort of protection mechanism.  */
 108 #if !DONE
 109 UTYPE
 110 SIZE(libat_exchange) (UTYPE *mptr, UTYPE newval, int smodel UNUSED)
 111 {
 112   UTYPE oldval;
 113   UWORD magic;
 114
 115   pre_seq_barrier (smodel);
 116   magic = protect_start (mptr);
 117
 118   oldval = *mptr;
 119   *mptr = newval;
 120
 121   protect_end (mptr, magic);
 122   post_seq_barrier (smodel);
 123
 124   return oldval;
 125 }
 126 #endif
 127
 128 EXPORT_ALIAS (SIZE(exchange));