libatomic/tas_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_TAS_N
  26 #include "libatomic_i.h"
  27
  28
  29 /* If we support the builtin, just use it.  */
  30 #if !DONE && SIZE(HAVE_ATOMIC_TAS)
  31 bool
  32 SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
  33 {
  34   if (maybe_specialcase_relaxed(smodel))
  35     return __atomic_test_and_set (mptr, __ATOMIC_RELAXED);
  36   else if (maybe_specialcase_acqrel(smodel))
  37     return __atomic_test_and_set (mptr, __ATOMIC_ACQ_REL);
  38   else
  39     return __atomic_test_and_set (mptr, __ATOMIC_SEQ_CST);
  40 }
  41
  42 #define DONE 1
  43 #endif /* HAVE_ATOMIC_TAS */
  44
  45
  46 /* If this type is smaller than word-sized, fall back to a word-sized
  47    compare-and-swap loop.  */
  48 #if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w)
  49 bool
  50 SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
  51 {
  52   UWORD wval, woldval, shift, *wptr, t;
  53
  54   pre_barrier (smodel);
  55
  56   if (N < WORDSIZE)
  57     {
  58       wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
  59       shift = SIZE(INVERT_MASK);
  60     }
  61   else
  62     {
  63       wptr = (UWORD *)mptr;
  64       shift = 0;
  65     }
  66
  67   wval = (UWORD)__GCC_ATOMIC_TEST_AND_SET_TRUEVAL << shift;
  68   woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
  69   do
  70     {
  71       t = woldval | wval;
  72     }
  73   while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
  74                                      __ATOMIC_RELAXED, __ATOMIC_RELAXED));
  75
  76   post_barrier (smodel);
  77   return (woldval & ((UTYPE) ~(UTYPE) 0 << shift)) != 0;
  78 }
  79
  80 #define DONE 1
  81 #endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */
  82
  83
  84 /* Otherwise, fall back to some sort of protection mechanism.  */
  85 #if !DONE && N == 1
  86 bool
  87 SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
  88 {
  89   UTYPE oldval;
  90   UWORD magic;
  91
  92   pre_seq_barrier (smodel);
  93   magic = protect_start (mptr);
  94
  95   oldval = *mptr;
  96   *mptr = __GCC_ATOMIC_TEST_AND_SET_TRUEVAL;
  97
  98   protect_end (mptr, magic);
  99   post_seq_barrier (smodel);
 100
 101   return oldval != 0;
 102 }
 103
 104 #define DONE 1
 105 #endif /* N == 1 */
 106
 107
 108 #if !DONE
 109 bool
 110 SIZE(libat_test_and_set) (UTYPE *mptr, int smodel UNUSED)
 111 {
 112   return libat_test_and_set_1 ((U_1 *)mptr, smodel);
 113 }
 114 #endif
 115
 116 EXPORT_ALIAS (SIZE(test_and_set));
 117 #undef LAT_TAS_N