1 /*-
2 * Copyright (c) 2011 Ed Schouten <ed@FreeBSD.org>
3 * David Chisnall <theraven@FreeBSD.org>
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 *
27 * $FreeBSD$
28 */
29
30 #ifndef _STDATOMIC_H_
31 #define _STDATOMIC_H_
32
33 #include <sys/cdefs.h>
34
35 #if defined(__cplusplus) && __cplusplus >= 201103L && defined(_USING_LIBCXX)
36 # ifdef __clang__
37 # if __has_feature(cxx_atomic)
38 # define _STDATOMIC_HAVE_ATOMIC
39 # endif
40 # else /* gcc */
41 # define _STDATOMIC_HAVE_ATOMIC
42 # endif
43 #endif
44
45 #ifdef _STDATOMIC_HAVE_ATOMIC
46
47 /* We have a usable C++ <atomic>; use it instead. */
48
49 #include <atomic>
50
51 #undef _Atomic
52 /* Also defined by <atomic> for gcc. But not used in macros. */
53 /* Also a clang intrinsic. */
54 /* Should not be used by client code before this file is */
55 /* included. The definitions in <atomic> themselves see */
56 /* the old definition, as they should. */
57 /* Client code sees the following definition. */
58
59 #define _Atomic(t) std::atomic<t>
60
61 using std::atomic_is_lock_free;
62 using std::atomic_init;
63 using std::atomic_store;
64 using std::atomic_store_explicit;
65 using std::atomic_load;
66 using std::atomic_load_explicit;
67 using std::atomic_exchange;
68 using std::atomic_exchange_explicit;
69 using std::atomic_compare_exchange_strong;
70 using std::atomic_compare_exchange_strong_explicit;
71 using std::atomic_compare_exchange_weak;
72 using std::atomic_compare_exchange_weak_explicit;
73 using std::atomic_fetch_add;
74 using std::atomic_fetch_add_explicit;
75 using std::atomic_fetch_sub;
76 using std::atomic_fetch_sub_explicit;
77 using std::atomic_fetch_or;
78 using std::atomic_fetch_or_explicit;
79 using std::atomic_fetch_xor;
80 using std::atomic_fetch_xor_explicit;
81 using std::atomic_fetch_and;
82 using std::atomic_fetch_and_explicit;
83 using std::atomic_thread_fence;
84 using std::atomic_signal_fence;
85
86 using std::memory_order;
87 using std::memory_order_relaxed;
88 using std::memory_order_consume;
89 using std::memory_order_acquire;
90 using std::memory_order_release;
91 using std::memory_order_acq_rel;
92 using std::memory_order_seq_cst;
93
94 using std::atomic_bool;
95 using std::atomic_char;
96 using std::atomic_schar;
97 using std::atomic_uchar;
98 using std::atomic_short;
99 using std::atomic_ushort;
100 using std::atomic_int;
101 using std::atomic_uint;
102 using std::atomic_long;
103 using std::atomic_ulong;
104 using std::atomic_llong;
105 using std::atomic_ullong;
106 using std::atomic_char16_t;
107 using std::atomic_char32_t;
108 using std::atomic_wchar_t;
109 using std::atomic_int_least8_t;
110 using std::atomic_uint_least8_t;
111 using std::atomic_int_least16_t;
112 using std::atomic_uint_least16_t;
113 using std::atomic_int_least32_t;
114 using std::atomic_uint_least32_t;
115 using std::atomic_int_least64_t;
116 using std::atomic_uint_least64_t;
117 using std::atomic_int_fast8_t;
118 using std::atomic_uint_fast8_t;
119 using std::atomic_int_fast16_t;
120 using std::atomic_uint_fast16_t;
121 using std::atomic_int_fast32_t;
122 using std::atomic_uint_fast32_t;
123 using std::atomic_int_fast64_t;
124 using std::atomic_uint_fast64_t;
125 using std::atomic_intptr_t;
126 using std::atomic_uintptr_t;
127 using std::atomic_size_t;
128 using std::atomic_ptrdiff_t;
129 using std::atomic_intmax_t;
130 using std::atomic_uintmax_t;
131
132 #else /* <atomic> unavailable, possibly because this is C, not C++ */
133
134 #include <sys/types.h>
135 #include <stdbool.h>
136
137 /*
138 * C: Do it ourselves.
139 * Note that the runtime representation defined here should be compatible
140 * with the C++ one, i.e. an _Atomic(T) needs to contain the same
141 * bits as a T.
142 */
143
144 #include <stddef.h> /* For ptrdiff_t. */
145 #include <stdint.h> /* TODO: don't drag in all the macros, just the types. */
146 // Include uchar.h only when needed. Bionic's stdatomic.h is also used for the
147 // host (via a copy in prebuilts/clang) and uchar.h is not available in the
148 // glibc used for the host.
149 #if __STDC_VERSION__ >= 201112L
150 # include <uchar.h> /* For char16_t and char32_t. */
151 #endif
152
153
154 #ifdef __clang__
155 # if __has_extension(c_atomic) || __has_extension(cxx_atomic)
156 # define __CLANG_ATOMICS
157 # else
158 # error "stdatomic.h does not support your compiler"
159 # endif
160 # if __has_builtin(__sync_swap)
161 # define __HAS_BUILTIN_SYNC_SWAP
162 # endif
163 #else
164 # define __GNUC_ATOMICS
165 #endif
166
167 /*
168 * 7.17.1 Atomic lock-free macros.
169 */
170
171 #ifdef __GCC_ATOMIC_BOOL_LOCK_FREE
172 #define ATOMIC_BOOL_LOCK_FREE __GCC_ATOMIC_BOOL_LOCK_FREE
173 #endif
174 #ifdef __GCC_ATOMIC_CHAR_LOCK_FREE
175 #define ATOMIC_CHAR_LOCK_FREE __GCC_ATOMIC_CHAR_LOCK_FREE
176 #endif
177 #ifdef __GCC_ATOMIC_CHAR16_T_LOCK_FREE
178 #define ATOMIC_CHAR16_T_LOCK_FREE __GCC_ATOMIC_CHAR16_T_LOCK_FREE
179 #endif
180 #ifdef __GCC_ATOMIC_CHAR32_T_LOCK_FREE
181 #define ATOMIC_CHAR32_T_LOCK_FREE __GCC_ATOMIC_CHAR32_T_LOCK_FREE
182 #endif
183 #ifdef __GCC_ATOMIC_WCHAR_T_LOCK_FREE
184 #define ATOMIC_WCHAR_T_LOCK_FREE __GCC_ATOMIC_WCHAR_T_LOCK_FREE
185 #endif
186 #ifdef __GCC_ATOMIC_SHORT_LOCK_FREE
187 #define ATOMIC_SHORT_LOCK_FREE __GCC_ATOMIC_SHORT_LOCK_FREE
188 #endif
189 #ifdef __GCC_ATOMIC_INT_LOCK_FREE
190 #define ATOMIC_INT_LOCK_FREE __GCC_ATOMIC_INT_LOCK_FREE
191 #endif
192 #ifdef __GCC_ATOMIC_LONG_LOCK_FREE
193 #define ATOMIC_LONG_LOCK_FREE __GCC_ATOMIC_LONG_LOCK_FREE
194 #endif
195 #ifdef __GCC_ATOMIC_LLONG_LOCK_FREE
196 #define ATOMIC_LLONG_LOCK_FREE __GCC_ATOMIC_LLONG_LOCK_FREE
197 #endif
198 #ifdef __GCC_ATOMIC_POINTER_LOCK_FREE
199 #define ATOMIC_POINTER_LOCK_FREE __GCC_ATOMIC_POINTER_LOCK_FREE
200 #endif
201
202 /*
203 * 7.17.2 Initialization.
204 */
205
206 #if defined(__CLANG_ATOMICS)
207 #define ATOMIC_VAR_INIT(value) (value)
208 #define atomic_init(obj, value) __c11_atomic_init(obj, value)
209 #else
210 #define ATOMIC_VAR_INIT(value) { .__val = (value) }
211 #define atomic_init(obj, value) ((void)((obj)->__val = (value)))
212 #endif
213
214 /*
215 * Clang and recent GCC both provide predefined macros for the memory
216 * orderings. If we are using a compiler that doesn't define them, use the
217 * clang values - these will be ignored in the fallback path.
218 */
219
220 #ifndef __ATOMIC_RELAXED
221 #define __ATOMIC_RELAXED 0
222 #endif
223 #ifndef __ATOMIC_CONSUME
224 #define __ATOMIC_CONSUME 1
225 #endif
226 #ifndef __ATOMIC_ACQUIRE
227 #define __ATOMIC_ACQUIRE 2
228 #endif
229 #ifndef __ATOMIC_RELEASE
230 #define __ATOMIC_RELEASE 3
231 #endif
232 #ifndef __ATOMIC_ACQ_REL
233 #define __ATOMIC_ACQ_REL 4
234 #endif
235 #ifndef __ATOMIC_SEQ_CST
236 #define __ATOMIC_SEQ_CST 5
237 #endif
238
239 /*
240 * 7.17.3 Order and consistency.
241 *
242 * The memory_order_* constants that denote the barrier behaviour of the
243 * atomic operations.
244 * The enum values must be identical to those used by the
245 * C++ <atomic> header.
246 */
247
248 typedef enum {
249 memory_order_relaxed = __ATOMIC_RELAXED,
250 memory_order_consume = __ATOMIC_CONSUME,
251 memory_order_acquire = __ATOMIC_ACQUIRE,
252 memory_order_release = __ATOMIC_RELEASE,
253 memory_order_acq_rel = __ATOMIC_ACQ_REL,
254 memory_order_seq_cst = __ATOMIC_SEQ_CST
255 } memory_order;
256
257 /*
258 * 7.17.4 Fences.
259 */
260
261 static __inline void
atomic_thread_fence(memory_order __order)262 atomic_thread_fence(memory_order __order __attribute__((unused)))
263 {
264
265 #ifdef __CLANG_ATOMICS
266 __c11_atomic_thread_fence(__order);
267 #elif defined(__GNUC_ATOMICS)
268 __atomic_thread_fence(__order);
269 #else
270 __sync_synchronize();
271 #endif
272 }
273
274 static __inline void
atomic_signal_fence(memory_order __order)275 atomic_signal_fence(memory_order __order __attribute__((unused)))
276 {
277
278 #ifdef __CLANG_ATOMICS
279 __c11_atomic_signal_fence(__order);
280 #elif defined(__GNUC_ATOMICS)
281 __atomic_signal_fence(__order);
282 #else
283 __asm volatile ("" ::: "memory");
284 #endif
285 }
286
287 /*
288 * 7.17.5 Lock-free property.
289 */
290
291 #if defined(_KERNEL)
292 /* Atomics in kernelspace are always lock-free. */
293 #define atomic_is_lock_free(obj) \
294 ((void)(obj), (_Bool)1)
295 #elif defined(__CLANG_ATOMICS)
296 #define atomic_is_lock_free(obj) \
297 __c11_atomic_is_lock_free(sizeof(*(obj)))
298 #elif defined(__GNUC_ATOMICS)
299 #define atomic_is_lock_free(obj) \
300 __atomic_is_lock_free(sizeof((obj)->__val), &(obj)->__val)
301 #else
302 #define atomic_is_lock_free(obj) \
303 ((void)(obj), sizeof((obj)->__val) <= sizeof(void *))
304 #endif
305
306 /*
307 * 7.17.6 Atomic integer types.
308 */
309
310 #ifndef __CLANG_ATOMICS
311 /*
312 * No native support for _Atomic(). Place object in structure to prevent
313 * most forms of direct non-atomic access.
314 */
315 #define _Atomic(T) struct { T volatile __val; }
316 #endif
317
318 typedef _Atomic(bool) atomic_bool;
319 typedef _Atomic(char) atomic_char;
320 typedef _Atomic(signed char) atomic_schar;
321 typedef _Atomic(unsigned char) atomic_uchar;
322 typedef _Atomic(short) atomic_short;
323 typedef _Atomic(unsigned short) atomic_ushort;
324 typedef _Atomic(int) atomic_int;
325 typedef _Atomic(unsigned int) atomic_uint;
326 typedef _Atomic(long) atomic_long;
327 typedef _Atomic(unsigned long) atomic_ulong;
328 typedef _Atomic(long long) atomic_llong;
329 typedef _Atomic(unsigned long long) atomic_ullong;
330 #if __STDC_VERSION__ >= 201112L || __cplusplus >= 201103L
331 typedef _Atomic(char16_t) atomic_char16_t;
332 typedef _Atomic(char32_t) atomic_char32_t;
333 #endif
334 typedef _Atomic(wchar_t) atomic_wchar_t;
335 typedef _Atomic(int_least8_t) atomic_int_least8_t;
336 typedef _Atomic(uint_least8_t) atomic_uint_least8_t;
337 typedef _Atomic(int_least16_t) atomic_int_least16_t;
338 typedef _Atomic(uint_least16_t) atomic_uint_least16_t;
339 typedef _Atomic(int_least32_t) atomic_int_least32_t;
340 typedef _Atomic(uint_least32_t) atomic_uint_least32_t;
341 typedef _Atomic(int_least64_t) atomic_int_least64_t;
342 typedef _Atomic(uint_least64_t) atomic_uint_least64_t;
343 typedef _Atomic(int_fast8_t) atomic_int_fast8_t;
344 typedef _Atomic(uint_fast8_t) atomic_uint_fast8_t;
345 typedef _Atomic(int_fast16_t) atomic_int_fast16_t;
346 typedef _Atomic(uint_fast16_t) atomic_uint_fast16_t;
347 typedef _Atomic(int_fast32_t) atomic_int_fast32_t;
348 typedef _Atomic(uint_fast32_t) atomic_uint_fast32_t;
349 typedef _Atomic(int_fast64_t) atomic_int_fast64_t;
350 typedef _Atomic(uint_fast64_t) atomic_uint_fast64_t;
351 typedef _Atomic(intptr_t) atomic_intptr_t;
352 typedef _Atomic(uintptr_t) atomic_uintptr_t;
353 typedef _Atomic(size_t) atomic_size_t;
354 typedef _Atomic(ptrdiff_t) atomic_ptrdiff_t;
355 typedef _Atomic(intmax_t) atomic_intmax_t;
356 typedef _Atomic(uintmax_t) atomic_uintmax_t;
357
358 /*
359 * 7.17.7 Operations on atomic types.
360 */
361
362 /*
363 * Compiler-specific operations.
364 */
365
366 #if defined(__CLANG_ATOMICS)
367 #define atomic_compare_exchange_strong_explicit(object, expected, \
368 desired, success, failure) \
369 __c11_atomic_compare_exchange_strong(object, expected, desired, \
370 success, failure)
371 #define atomic_compare_exchange_weak_explicit(object, expected, \
372 desired, success, failure) \
373 __c11_atomic_compare_exchange_weak(object, expected, desired, \
374 success, failure)
375 #define atomic_exchange_explicit(object, desired, order) \
376 __c11_atomic_exchange(object, desired, order)
377 #define atomic_fetch_add_explicit(object, operand, order) \
378 __c11_atomic_fetch_add(object, operand, order)
379 #define atomic_fetch_and_explicit(object, operand, order) \
380 __c11_atomic_fetch_and(object, operand, order)
381 #define atomic_fetch_or_explicit(object, operand, order) \
382 __c11_atomic_fetch_or(object, operand, order)
383 #define atomic_fetch_sub_explicit(object, operand, order) \
384 __c11_atomic_fetch_sub(object, operand, order)
385 #define atomic_fetch_xor_explicit(object, operand, order) \
386 __c11_atomic_fetch_xor(object, operand, order)
387 #define atomic_load_explicit(object, order) \
388 __c11_atomic_load(object, order)
389 #define atomic_store_explicit(object, desired, order) \
390 __c11_atomic_store(object, desired, order)
391 #elif defined(__GNUC_ATOMICS)
392 #define atomic_compare_exchange_strong_explicit(object, expected, \
393 desired, success, failure) \
394 __atomic_compare_exchange_n(&(object)->__val, expected, \
395 desired, 0, success, failure)
396 #define atomic_compare_exchange_weak_explicit(object, expected, \
397 desired, success, failure) \
398 __atomic_compare_exchange_n(&(object)->__val, expected, \
399 desired, 1, success, failure)
400 #define atomic_exchange_explicit(object, desired, order) \
401 __atomic_exchange_n(&(object)->__val, desired, order)
402 #define atomic_fetch_add_explicit(object, operand, order) \
403 __atomic_fetch_add(&(object)->__val, operand, order)
404 #define atomic_fetch_and_explicit(object, operand, order) \
405 __atomic_fetch_and(&(object)->__val, operand, order)
406 #define atomic_fetch_or_explicit(object, operand, order) \
407 __atomic_fetch_or(&(object)->__val, operand, order)
408 #define atomic_fetch_sub_explicit(object, operand, order) \
409 __atomic_fetch_sub(&(object)->__val, operand, order)
410 #define atomic_fetch_xor_explicit(object, operand, order) \
411 __atomic_fetch_xor(&(object)->__val, operand, order)
412 #define atomic_load_explicit(object, order) \
413 __atomic_load_n(&(object)->__val, order)
414 #define atomic_store_explicit(object, desired, order) \
415 __atomic_store_n(&(object)->__val, desired, order)
416 #else
417 #define __atomic_apply_stride(object, operand) \
418 (((__typeof__((object)->__val))0) + (operand))
419 #define atomic_compare_exchange_strong_explicit(object, expected, \
420 desired, success, failure) __extension__ ({ \
421 __typeof__(expected) __ep = (expected); \
422 __typeof__(*__ep) __e = *__ep; \
423 (void)(success); (void)(failure); \
424 (bool)((*__ep = __sync_val_compare_and_swap(&(object)->__val, \
425 __e, desired)) == __e); \
426 })
427 #define atomic_compare_exchange_weak_explicit(object, expected, \
428 desired, success, failure) \
429 atomic_compare_exchange_strong_explicit(object, expected, \
430 desired, success, failure)
431 #ifdef __HAS_BUILTIN_SYNC_SWAP
432 /* Clang provides a full-barrier atomic exchange - use it if available. */
433 #define atomic_exchange_explicit(object, desired, order) \
434 ((void)(order), __sync_swap(&(object)->__val, desired))
435 #else
436 /*
437 * __sync_lock_test_and_set() is only an acquire barrier in theory (although in
438 * practice it is usually a full barrier) so we need an explicit barrier before
439 * it.
440 */
441 #define atomic_exchange_explicit(object, desired, order) \
442 __extension__ ({ \
443 __typeof__(object) __o = (object); \
444 __typeof__(desired) __d = (desired); \
445 (void)(order); \
446 __sync_synchronize(); \
447 __sync_lock_test_and_set(&(__o)->__val, __d); \
448 })
449 #endif
450 #define atomic_fetch_add_explicit(object, operand, order) \
451 ((void)(order), __sync_fetch_and_add(&(object)->__val, \
452 __atomic_apply_stride(object, operand)))
453 #define atomic_fetch_and_explicit(object, operand, order) \
454 ((void)(order), __sync_fetch_and_and(&(object)->__val, operand))
455 #define atomic_fetch_or_explicit(object, operand, order) \
456 ((void)(order), __sync_fetch_and_or(&(object)->__val, operand))
457 #define atomic_fetch_sub_explicit(object, operand, order) \
458 ((void)(order), __sync_fetch_and_sub(&(object)->__val, \
459 __atomic_apply_stride(object, operand)))
460 #define atomic_fetch_xor_explicit(object, operand, order) \
461 ((void)(order), __sync_fetch_and_xor(&(object)->__val, operand))
462 #define atomic_load_explicit(object, order) \
463 ((void)(order), __sync_fetch_and_add(&(object)->__val, 0))
464 #define atomic_store_explicit(object, desired, order) \
465 ((void)atomic_exchange_explicit(object, desired, order))
466 #endif
467
468 /*
469 * Convenience functions.
470 *
471 * Don't provide these in kernel space. In kernel space, we should be
472 * disciplined enough to always provide explicit barriers.
473 */
474
475 #ifndef _KERNEL
476 #define atomic_compare_exchange_strong(object, expected, desired) \
477 atomic_compare_exchange_strong_explicit(object, expected, \
478 desired, memory_order_seq_cst, memory_order_seq_cst)
479 #define atomic_compare_exchange_weak(object, expected, desired) \
480 atomic_compare_exchange_weak_explicit(object, expected, \
481 desired, memory_order_seq_cst, memory_order_seq_cst)
482 #define atomic_exchange(object, desired) \
483 atomic_exchange_explicit(object, desired, memory_order_seq_cst)
484 #define atomic_fetch_add(object, operand) \
485 atomic_fetch_add_explicit(object, operand, memory_order_seq_cst)
486 #define atomic_fetch_and(object, operand) \
487 atomic_fetch_and_explicit(object, operand, memory_order_seq_cst)
488 #define atomic_fetch_or(object, operand) \
489 atomic_fetch_or_explicit(object, operand, memory_order_seq_cst)
490 #define atomic_fetch_sub(object, operand) \
491 atomic_fetch_sub_explicit(object, operand, memory_order_seq_cst)
492 #define atomic_fetch_xor(object, operand) \
493 atomic_fetch_xor_explicit(object, operand, memory_order_seq_cst)
494 #define atomic_load(object) \
495 atomic_load_explicit(object, memory_order_seq_cst)
496 #define atomic_store(object, desired) \
497 atomic_store_explicit(object, desired, memory_order_seq_cst)
498 #endif /* !_KERNEL */
499
500 /*
501 * 7.17.8 Atomic flag type and operations.
502 *
503 * XXX: Assume atomic_bool can be used as an atomic_flag. Is there some
504 * kind of compiler built-in type we could use?
505 */
506
507 typedef struct {
508 atomic_bool __flag;
509 } atomic_flag;
510
511 #define ATOMIC_FLAG_INIT { ATOMIC_VAR_INIT(false) }
512
513 static __inline bool
atomic_flag_test_and_set_explicit(volatile atomic_flag * __object,memory_order __order)514 atomic_flag_test_and_set_explicit(volatile atomic_flag *__object,
515 memory_order __order)
516 {
517 return (atomic_exchange_explicit(&__object->__flag, 1, __order));
518 }
519
520 static __inline void
atomic_flag_clear_explicit(volatile atomic_flag * __object,memory_order __order)521 atomic_flag_clear_explicit(volatile atomic_flag *__object, memory_order __order)
522 {
523
524 atomic_store_explicit(&__object->__flag, 0, __order);
525 }
526
527 #ifndef _KERNEL
528 static __inline bool
atomic_flag_test_and_set(volatile atomic_flag * __object)529 atomic_flag_test_and_set(volatile atomic_flag *__object)
530 {
531
532 return (atomic_flag_test_and_set_explicit(__object,
533 memory_order_seq_cst));
534 }
535
536 static __inline void
atomic_flag_clear(volatile atomic_flag * __object)537 atomic_flag_clear(volatile atomic_flag *__object)
538 {
539
540 atomic_flag_clear_explicit(__object, memory_order_seq_cst);
541 }
542 #endif /* !_KERNEL */
543
544 #endif /* <atomic> unavailable */
545
546 #endif /* !_STDATOMIC_H_ */
547