libatomic/store_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_STORE_N
  26 #include "libatomic_i.h"
  27
  28
  29 /* If we support the builtin, just use it.  */
  30 #if !DONE && SIZE(HAVE_ATOMIC_LDST)
  31 void
  32 SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
  33 {
  34   if (maybe_specialcase_relaxed(smodel))
  35     __atomic_store_n (mptr, newval, __ATOMIC_RELAXED);
  36   else if (maybe_specialcase_acqrel(smodel))
  37     /* Note that ACQ and ACQ_REL are not valid for store.  */
  38     __atomic_store_n (mptr, newval, __ATOMIC_RELEASE);
  39   else
  40     __atomic_store_n (mptr, newval, __ATOMIC_SEQ_CST);
  41 }
  42
  43 #define DONE 1
  44 #endif /* HAVE_ATOMIC_STORE */
  45
  46 /* If we have compare-and-swap, use it perform the store.  */
  47 #if !DONE && defined(atomic_compare_exchange_n)
  48 void
  49 SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
  50 {
  51   UTYPE oldval;
  52
  53   pre_barrier (smodel);
  54
  55   oldval = *mptr;
  56   while (!atomic_compare_exchange_n (mptr, &oldval, newval, true,
  57                                      __ATOMIC_RELAXED, __ATOMIC_RELAXED))
  58     continue;
  59
  60   post_barrier (smodel);
  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 void
  71 SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
  72 {
  73   UWORD mask, shift, woldval, wnewval, t, *wptr;
  74
  75   pre_barrier (smodel);
  76
  77   wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
  78   shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
  79   mask = SIZE(MASK) << shift;
  80
  81   wnewval = (UWORD)newval << shift;
  82   woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
  83   do
  84     {
  85       t = (woldval & ~mask) | wnewval;
  86     }
  87   while (!atomic_compare_exchange_w (wptr, &woldval, t));
  88
  89   post_barrier (smodel);
  90 }
  91
  92 #define DONE 1
  93 #endif /* N < WORDSIZE && atomic_compare_exchange_w */
  94
  95
  96 /* Otherwise, fall back to some sort of protection mechanism.  */
  97 #if !DONE
  98 void
  99 SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
 100 {
 101   UWORD magic;
 102
 103   pre_seq_barrier (smodel);
 104   magic = protect_start (mptr);
 105
 106   *mptr = newval;
 107
 108   protect_end (mptr, magic);
 109   post_seq_barrier (smodel);
 110 }
 111 #endif
 112
 113 EXPORT_ALIAS (SIZE(store));
 114 #undef LAT_STORE_N