libatomic/store_n.c

   1 /* Copyright (C) 2012-2013 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_LDST)
  30 void
  31 SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
  32 {
  33   if (maybe_specialcase_relaxed(smodel))
  34     __atomic_store_n (mptr, newval, __ATOMIC_RELAXED);
  35   else if (maybe_specialcase_acqrel(smodel))
  36     /* Note that ACQ and ACQ_REL are not valid for store.  */
  37     __atomic_store_n (mptr, newval, __ATOMIC_RELEASE);
  38   else
  39     __atomic_store_n (mptr, newval, __ATOMIC_SEQ_CST);
  40 }
  41
  42 #define DONE 1
  43 #endif /* HAVE_ATOMIC_STORE */
  44
  45 /* If we have compare-and-swap, use it perform the store.  */
  46 #if !DONE && defined(atomic_compare_exchange_n)
  47 void
  48 SIZE(libat_store) (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
  62 #define DONE 1
  63 #endif /* atomic_compare_exchange_n */
  64
  65
  66 /* If this type is smaller than word-sized, fall back to a word-sized
  67    compare-and-swap loop.  */
  68 #if !DONE && N < WORDSIZE && defined(atomic_compare_exchange_w)
  69 void
  70 SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
  71 {
  72   UWORD mask, shift, woldval, wnewval, t, *wptr;
  73
  74   pre_barrier (smodel);
  75
  76   wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
  77   shift = (((uintptr_t)mptr % WORDSIZE) * CHAR_BIT) ^ SIZE(INVERT_MASK);
  78   mask = SIZE(MASK) << shift;
  79
  80   wnewval = (UWORD)newval << shift;
  81   woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
  82   do
  83     {
  84       t = (woldval & ~mask) | wnewval;
  85     }
  86   while (!atomic_compare_exchange_w (wptr, &woldval, t));
  87
  88   post_barrier (smodel);
  89 }
  90
  91 #define DONE 1
  92 #endif /* N < WORDSIZE && atomic_compare_exchange_w */
  93
  94
  95 /* Otherwise, fall back to some sort of protection mechanism.  */
  96 #if !DONE
  97 void
  98 SIZE(libat_store) (UTYPE *mptr, UTYPE newval, int smodel)
  99 {
 100   UWORD magic;
 101
 102   pre_seq_barrier (smodel);
 103   magic = protect_start (mptr);
 104
 105   *mptr = newval;
 106
 107   protect_end (mptr, magic);
 108   post_seq_barrier (smodel);
 109 }
 110 #endif
 111
 112 EXPORT_ALIAS (SIZE(store));