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 natively support the exchange, and if we're unconcerned with extra
      29     barriers (e.g. fully in-order cpu for which barriers are a nop), then
      30     go ahead and expand the operation inline.  */
      31  #if !defined(WANT_SPECIALCASE_RELAXED) && !defined(__OPTIMIZE_SIZE__)
      32  # define EXACT_INLINE(N)					\
      33    if (C2(HAVE_ATOMIC_EXCHANGE_,N))				\
      34      {								\
      35        *PTR(N,rptr) = __atomic_exchange_n			\
      36  	(PTR(N,mptr), *PTR(N,vptr), __ATOMIC_SEQ_CST);		\
      37        return;							\
      38      }
      39  #else
      40  # define EXACT_INLINE(N)
      41  #endif
      42  
      43  
      44  #define EXACT(N)						\
      45    do {								\
      46      if (!C2(HAVE_INT,N)) break;					\
      47      if ((uintptr_t)mptr & (N - 1)) break;			\
      48      EXACT_INLINE (N);						\
      49      *PTR(N,rptr) = C3(local_,exchange_,N)			\
      50        (PTR(N,mptr), *PTR(N,vptr), smodel);			\
      51      return;							\
      52    } while (0)
      53  
      54  
      55  #define LARGER(N)						\
      56    do {								\
      57      if (!C2(HAVE_INT,N)) break;					\
      58      if (!C2(MAYBE_HAVE_ATOMIC_CAS_,N)) break;			\
      59      r = (uintptr_t)mptr & (N - 1);				\
      60      a = (uintptr_t)mptr & -N;					\
      61      if (r + n <= N)						\
      62        {								\
      63  	pre_barrier (smodel);					\
      64  	u.C2(i,N) = *PTR(N,a);					\
      65  	do {							\
      66  	  v = u;						\
      67  	  memcpy (v.b + r, vptr, n);				\
      68  	} while (!(C2(HAVE_ATOMIC_CAS_,N)			\
      69  		   ? __atomic_compare_exchange_n (PTR(N,a),	\
      70  			&u.C2(i,N), v.C2(i,N), true,		\
      71  			__ATOMIC_RELAXED, __ATOMIC_RELAXED)	\
      72  		   : C3(local_,compare_exchange_,N) (PTR(N,a),	\
      73  			&u.C2(i,N), v.C2(i,N),			\
      74  			__ATOMIC_RELAXED, __ATOMIC_RELAXED)));	\
      75  	goto Lfinish;						\
      76        }								\
      77    } while (0)
      78  
      79  
      80  static void __attribute__((noinline))
      81  libat_exchange_large_inplace (size_t n, void *mptr, void *vptr)
      82  {
      83  #define BUF	1024
      84  
      85    char temp[BUF];
      86    size_t i = 0;
      87  
      88    for (i = 0; n >= BUF; i += BUF, n -= BUF)
      89      {
      90        memcpy (temp, mptr + i, BUF);
      91        memcpy (mptr + i, vptr + i, BUF);
      92        memcpy (vptr + i, temp, BUF);
      93      }
      94    if (n > 0)
      95      {
      96        memcpy (temp, mptr + i, n);
      97        memcpy (mptr + i, vptr + i, n);
      98        memcpy (vptr + i, temp, n);
      99      }
     100  
     101  #undef BUF
     102  }
     103  
     104  void
     105  libat_exchange (size_t n, void *mptr, void *vptr, void *rptr, int smodel)
     106  {
     107    union max_size_u u, v;
     108    uintptr_t r, a;
     109  
     110    switch (n)
     111      {
     112      case 0:				return;
     113      case 1:		EXACT(1);	goto L4;
     114      case 2:		EXACT(2);	goto L4;
     115      case 4:		EXACT(4);	goto L8;
     116      case 8:		EXACT(8);	goto L16;
     117      case 16:		EXACT(16);	break;
     118  
     119      case 3: L4:		LARGER(4);	/* FALLTHRU */
     120      case 5 ... 7: L8:	LARGER(8);	/* FALLTHRU */
     121      case 9 ... 15: L16:	LARGER(16);	break;
     122  
     123      Lfinish:
     124        post_barrier (smodel);
     125        memcpy (rptr, u.b + r, n);
     126        return;
     127      }
     128  
     129    pre_seq_barrier (smodel);
     130    libat_lock_n (mptr, n);
     131  
     132    if (vptr != rptr)
     133      {
     134        memcpy (rptr, mptr, n);
     135        memcpy (mptr, vptr, n);
     136      }
     137    else
     138      libat_exchange_large_inplace (n, mptr, vptr);
     139  
     140    libat_unlock_n (mptr, n);
     141    post_seq_barrier (smodel);
     142  }
     143  
     144  EXPORT_ALIAS (exchange);