1  /* Copyright (C) 2012-2023 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_TAS)
      30  bool
      31  SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
      32  {
      33    if (maybe_specialcase_relaxed(smodel))
      34      return __atomic_test_and_set (mptr, __ATOMIC_RELAXED);
      35    else if (maybe_specialcase_acqrel(smodel))
      36      return __atomic_test_and_set (mptr, __ATOMIC_ACQ_REL);
      37    else
      38      return __atomic_test_and_set (mptr, __ATOMIC_SEQ_CST);
      39  }
      40  
      41  #define DONE 1
      42  #endif /* HAVE_ATOMIC_TAS */
      43  
      44  
      45  /* If this type is smaller than word-sized, fall back to a word-sized
      46     compare-and-swap loop.  */
      47  #if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w)
      48  bool
      49  SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
      50  {
      51    UWORD wval, woldval, shift, *wptr, t;
      52  
      53    pre_barrier (smodel);
      54  
      55    if (N < WORDSIZE)
      56      {
      57        wptr = (UWORD *)((uintptr_t)mptr & -WORDSIZE);
      58        shift = SIZE(INVERT_MASK);
      59      }
      60    else
      61      {
      62        wptr = (UWORD *)mptr;
      63        shift = 0;
      64      }
      65  
      66    wval = (UWORD)__GCC_ATOMIC_TEST_AND_SET_TRUEVAL << shift;
      67    woldval = __atomic_load_n (wptr, __ATOMIC_RELAXED);
      68    do
      69      {
      70        t = woldval | wval;
      71      }
      72    while (!atomic_compare_exchange_w (wptr, &woldval, t, true,
      73  				     __ATOMIC_RELAXED, __ATOMIC_RELAXED));
      74  
      75    post_barrier (smodel);
      76    return (woldval & ((UTYPE) ~(UTYPE) 0 << shift)) != 0;
      77  }
      78  
      79  #define DONE 1
      80  #endif /* HAVE_ATOMIC_CAS && N < WORDSIZE */
      81  
      82  
      83  /* Otherwise, fall back to some sort of protection mechanism.  */
      84  #if !DONE && N == 1
      85  bool
      86  SIZE(libat_test_and_set) (UTYPE *mptr, int smodel)
      87  {
      88    UTYPE oldval;
      89    UWORD magic;
      90  
      91    pre_seq_barrier (smodel);
      92    magic = protect_start (mptr);
      93  
      94    oldval = *mptr;
      95    *mptr = __GCC_ATOMIC_TEST_AND_SET_TRUEVAL;
      96  
      97    protect_end (mptr, magic);
      98    post_seq_barrier (smodel);
      99  
     100    return oldval != 0;
     101  }
     102  
     103  #define DONE 1
     104  #endif /* N == 1 */
     105  
     106  
     107  #if !DONE
     108  bool
     109  SIZE(libat_test_and_set) (UTYPE *mptr, int smodel UNUSED)
     110  {
     111    return libat_test_and_set_1 ((U_1 *)mptr, smodel);
     112  }
     113  #endif
     114  
     115  EXPORT_ALIAS (SIZE(test_and_set));