1 /* Copyright (C) 2012-2020 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))
libat_exchange_large_inplace(size_t n,void * mptr,void * vptr)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
libat_exchange(size_t n,void * mptr,void * vptr,void * rptr,int smodel)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);
145