--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libatomic/gexch.c	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,144 @@
+/* Copyright (C) 2012-2017 Free Software Foundation, Inc.
+   Contributed by Richard Henderson <rth@redhat.com>.
+
+   This file is part of the GNU Atomic Library (libatomic).
+
+   Libatomic is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   Libatomic is distributed in the hope that it will be useful, but WITHOUT ANY
+   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+   FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+   more details.
+
+   Under Section 7 of GPL version 3, you are granted additional
+   permissions described in the GCC Runtime Library Exception, version
+   3.1, as published by the Free Software Foundation.
+
+   You should have received a copy of the GNU General Public License and
+   a copy of the GCC Runtime Library Exception along with this program;
+   see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include "libatomic_i.h"
+
+
+/* If we natively support the exchange, and if we're unconcerned with extra
+   barriers (e.g. fully in-order cpu for which barriers are a nop), then
+   go ahead and expand the operation inline.  */
+#if !defined(WANT_SPECIALCASE_RELAXED) && !defined(__OPTIMIZE_SIZE__)
+# define EXACT_INLINE(N)					\
+  if (C2(HAVE_ATOMIC_EXCHANGE_,N))				\
+    {								\
+      *PTR(N,rptr) = __atomic_exchange_n			\
+	(PTR(N,mptr), *PTR(N,vptr), __ATOMIC_SEQ_CST);		\
+      return;							\
+    }
+#else
+# define EXACT_INLINE(N)
+#endif
+
+
+#define EXACT(N)						\
+  do {								\
+    if (!C2(HAVE_INT,N)) break;					\
+    if ((uintptr_t)mptr & (N - 1)) break;			\
+    EXACT_INLINE (N);						\
+    *PTR(N,rptr) = C3(local_,exchange_,N)			\
+      (PTR(N,mptr), *PTR(N,vptr), smodel);			\
+    return;							\
+  } while (0)
+
+
+#define LARGER(N)						\
+  do {								\
+    if (!C2(HAVE_INT,N)) break;					\
+    if (!C2(MAYBE_HAVE_ATOMIC_CAS_,N)) break;			\
+    r = (uintptr_t)mptr & (N - 1);				\
+    a = (uintptr_t)mptr & -N;					\
+    if (r + n <= N)						\
+      {								\
+	pre_barrier (smodel);					\
+	u.C2(i,N) = *PTR(N,a);					\
+	do {							\
+	  v = u;						\
+	  memcpy (v.b + r, vptr, n);				\
+	} while (!(C2(HAVE_ATOMIC_CAS_,N)			\
+		   ? __atomic_compare_exchange_n (PTR(N,a),	\
+			&u.C2(i,N), v.C2(i,N), true,		\
+			__ATOMIC_RELAXED, __ATOMIC_RELAXED)	\
+		   : C3(local_,compare_exchange_,N) (PTR(N,a),	\
+			&u.C2(i,N), v.C2(i,N),			\
+			__ATOMIC_RELAXED, __ATOMIC_RELAXED)));	\
+	goto Lfinish;						\
+      }								\
+  } while (0)
+
+
+static void __attribute__((noinline))
+libat_exchange_large_inplace (size_t n, void *mptr, void *vptr)
+{
+#define BUF	1024
+
+  char temp[BUF];
+  size_t i = 0;
+
+  for (i = 0; n >= BUF; i += BUF, n -= BUF)
+    {
+      memcpy (temp, mptr + i, BUF);
+      memcpy (mptr + i, vptr + i, BUF);
+      memcpy (vptr + i, temp, BUF);
+    }
+  if (n > 0)
+    {
+      memcpy (temp, mptr + i, n);
+      memcpy (mptr + i, vptr + i, n);
+      memcpy (vptr + i, temp, n);
+    }
+
+#undef BUF
+}
+
+void
+libat_exchange (size_t n, void *mptr, void *vptr, void *rptr, int smodel)
+{
+  union max_size_u u, v;
+  uintptr_t r, a;
+
+  switch (n)
+    {
+    case 0:				return;
+    case 1:		EXACT(1);	goto L4;
+    case 2:		EXACT(2);	goto L4;
+    case 4:		EXACT(4);	goto L8;
+    case 8:		EXACT(8);	goto L16;
+    case 16:		EXACT(16);	break;
+
+    case 3: L4:		LARGER(4);	/* FALLTHRU */
+    case 5 ... 7: L8:	LARGER(8);	/* FALLTHRU */
+    case 9 ... 15: L16:	LARGER(16);	break;
+
+    Lfinish:
+      post_barrier (smodel);
+      memcpy (rptr, u.b + r, n);
+      return;
+    }
+
+  pre_seq_barrier (smodel);
+  libat_lock_n (mptr, n);
+
+  if (vptr != rptr)
+    {
+      memcpy (rptr, mptr, n);
+      memcpy (mptr, vptr, n);
+    }
+  else
+    libat_exchange_large_inplace (n, mptr, vptr);
+
+  libat_unlock_n (mptr, n);
+  post_seq_barrier (smodel);
+}
+
+EXPORT_ALIAS (exchange);