text: /*-
   * Copyright (c) 2011 Ed Schouten <ed@FreeBSD.org>
   *                    David Chisnall <theraven@FreeBSD.org>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   * $FreeBSD$
   */
  
  #ifndef _STDATOMIC_H_
  #define	_STDATOMIC_H_
  
  #include <sys/cdefs.h>
  
  #if defined(__GNUC__) && !defined(__GNUC_PREREQ)
  /* Duplicate definition here, since the mingw sys/cdefs.h omits the  */
  /* definition, and this needs to be usable there.                    */
  #define	__GNUC_PREREQ(x, y)    \
  	((__GNUC__ == (x) && __GNUC_MINOR__ >= (y)) || (__GNUC__ > (x)))
  #endif /* __GNUC__ && ... */
  
  #if defined(__cplusplus) && __cplusplus >= 201103L && defined(_USING_LIBCXX)
  # ifdef __clang__
  #  if __has_feature(cxx_atomic)
  #   define _STDATOMIC_HAVE_ATOMIC
  #  endif
  # else /* gcc */
  #  if __GNUC_PREREQ(4, 7)
  #   define _STDATOMIC_HAVE_ATOMIC
  #  endif
  # endif
  #endif
  
  #ifdef _STDATOMIC_HAVE_ATOMIC
  
  /* We have a usable C++ <atomic>; use it instead.  */
  
  #include <atomic>
  
  #undef _Atomic
          /* Also defined by <atomic> for gcc.  But not used in macros. */
          /* Also a clang intrinsic.                                    */
          /* Should not be used by client code before this file is      */
          /* included.  The definitions in <atomic> themselves see      */
          /* the old definition, as they should.                        */
          /* Client code sees the following definition.                 */
  
  #define _Atomic(t) std::atomic<t>
  
  using std::atomic_is_lock_free;
  using std::atomic_init;
  using std::atomic_store;
  using std::atomic_store_explicit;
  using std::atomic_load;
  using std::atomic_load_explicit;
  using std::atomic_exchange;
  using std::atomic_exchange_explicit;
  using std::atomic_compare_exchange_strong;
  using std::atomic_compare_exchange_strong_explicit;
  using std::atomic_compare_exchange_weak;
  using std::atomic_compare_exchange_weak_explicit;
  using std::atomic_fetch_add;
  using std::atomic_fetch_add_explicit;
  using std::atomic_fetch_sub;
  using std::atomic_fetch_sub_explicit;
  using std::atomic_fetch_or;
  using std::atomic_fetch_or_explicit;
  using std::atomic_fetch_xor;
  using std::atomic_fetch_xor_explicit;
  using std::atomic_fetch_and;
  using std::atomic_fetch_and_explicit;
  using std::atomic_thread_fence;
  using std::atomic_signal_fence;
  
  using std::memory_order;
  using std::memory_order_relaxed;
  using std::memory_order_consume;
  using std::memory_order_acquire;
  using std::memory_order_release;
  using std::memory_order_acq_rel;
  using std::memory_order_seq_cst;
  
  using std::atomic_bool;
  using std::atomic_char;
  using std::atomic_schar;
  using std::atomic_uchar;
  using std::atomic_short;
  using std::atomic_ushort;
  using std::atomic_int;
  using std::atomic_uint;
  using std::atomic_long;
  using std::atomic_ulong;
  using std::atomic_llong;
  using std::atomic_ullong;
  using std::atomic_char16_t;
  using std::atomic_char32_t;
  using std::atomic_wchar_t;
  using std::atomic_int_least8_t;
  using std::atomic_uint_least8_t;
  using std::atomic_int_least16_t;
  using std::atomic_uint_least16_t;
  using std::atomic_int_least32_t;
  using std::atomic_uint_least32_t;
  using std::atomic_int_least64_t;
  using std::atomic_uint_least64_t;
  using std::atomic_int_fast8_t;
  using std::atomic_uint_fast8_t;
  using std::atomic_int_fast16_t;
  using std::atomic_uint_fast16_t;
  using std::atomic_int_fast32_t;
  using std::atomic_uint_fast32_t;
  using std::atomic_int_fast64_t;
  using std::atomic_uint_fast64_t;
  using std::atomic_intptr_t;
  using std::atomic_uintptr_t;
  using std::atomic_size_t;
  using std::atomic_ptrdiff_t;
  using std::atomic_intmax_t;
  using std::atomic_uintmax_t;
  
  #else /* <atomic> unavailable, possibly because this is C, not C++ */
  
  #include <sys/types.h>
  #include <stdbool.h>
  
  /*
   * C: Do it ourselves.
   * Note that the runtime representation defined here should be compatible
   * with the C++ one, i.e. an _Atomic(T) needs to contain the same
   * bits as a T.
   */
  
  #include <stddef.h>  /* For ptrdiff_t.                          */
  #include <stdint.h>  /* TODO: Should pollute namespace less.    */
  #if __STDC_VERSION__ >= 201112L
  # include <uchar.h>  /* For char16_t and char32_t.              */
  #endif
  
  #ifdef __clang__
  # if __has_extension(c_atomic) || __has_extension(cxx_atomic)
  #  define       __CLANG_ATOMICS
  # else
  #  error "stdatomic.h does not support your compiler"
  # endif
  # if __has_builtin(__sync_swap)
  #  define __HAS_BUILTIN_SYNC_SWAP
  # endif
  #else
  # if __GNUC_PREREQ(4, 7)
  #  define	__GNUC_ATOMICS
  # else
  #  define	__SYNC_ATOMICS
  #  ifdef __cplusplus
  #   define       __ATOMICS_AVOID_DOT_INIT
  #  endif
  # endif
  #endif
  
  /*
   * 7.17.1 Atomic lock-free macros.
   */
  
  #ifdef __GCC_ATOMIC_BOOL_LOCK_FREE
  #define	ATOMIC_BOOL_LOCK_FREE		__GCC_ATOMIC_BOOL_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_BOOL_LOCK_FREE           2 /* For all modern platforms */
  #endif
  #ifdef __GCC_ATOMIC_CHAR_LOCK_FREE
  #define	ATOMIC_CHAR_LOCK_FREE		__GCC_ATOMIC_CHAR_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_CHAR_LOCK_FREE           2
  #endif
  #ifdef __GCC_ATOMIC_CHAR16_T_LOCK_FREE
  #define	ATOMIC_CHAR16_T_LOCK_FREE	__GCC_ATOMIC_CHAR16_T_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_CHAR16_T_LOCK_FREE       2
  #endif
  #ifdef __GCC_ATOMIC_CHAR32_T_LOCK_FREE
  #define	ATOMIC_CHAR32_T_LOCK_FREE	__GCC_ATOMIC_CHAR32_T_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_CHAR32_T_LOCK_FREE       2
  #endif
  #ifdef __GCC_ATOMIC_WCHAR_T_LOCK_FREE
  #define	ATOMIC_WCHAR_T_LOCK_FREE	__GCC_ATOMIC_WCHAR_T_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_WCHAR_T_LOCK_FREE        2
  #endif
  #ifdef __GCC_ATOMIC_SHORT_LOCK_FREE
  #define	ATOMIC_SHORT_LOCK_FREE		__GCC_ATOMIC_SHORT_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_SHORT_LOCK_FREE          2
  #endif
  #ifdef __GCC_ATOMIC_INT_LOCK_FREE
  #define	ATOMIC_INT_LOCK_FREE		__GCC_ATOMIC_INT_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_INT_LOCK_FREE            2
  #endif
  #ifdef __GCC_ATOMIC_LONG_LOCK_FREE
  #define	ATOMIC_LONG_LOCK_FREE		__GCC_ATOMIC_LONG_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_LONG_LOCK_FREE           2
  #endif
  #ifdef __GCC_ATOMIC_LLONG_LOCK_FREE
  #define	ATOMIC_LLONG_LOCK_FREE		__GCC_ATOMIC_LLONG_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_LLONG_LOCK_FREE          1 /* maybe */
  #endif
  #ifdef __GCC_ATOMIC_POINTER_LOCK_FREE
  #define	ATOMIC_POINTER_LOCK_FREE	__GCC_ATOMIC_POINTER_LOCK_FREE
  #elif defined(__SYNC_ATOMICS)
  #define	ATOMIC_POINTER_LOCK_FREE        2
  #endif
  
  /*
   * 7.17.2 Initialization.
   */
  
  #if defined(__CLANG_ATOMICS)
  #define	ATOMIC_VAR_INIT(value)		(value)
  #define	atomic_init(obj, value)		__c11_atomic_init(obj, value)
  #else
  #ifdef __ATOMICS_AVOID_DOT_INIT
  #define	ATOMIC_VAR_INIT(value)		{ value }
  #else
  #define	ATOMIC_VAR_INIT(value)		{ .__val = (value) }
  #endif
  #define	atomic_init(obj, value)		((void)((obj)->__val = (value)))
  #endif
  
  /*
   * Clang and recent GCC both provide predefined macros for the memory
   * orderings.  If we are using a compiler that doesn't define them, use the
   * clang values - these will be ignored in the fallback path.
   */
  
  #ifndef __ATOMIC_RELAXED
  #define __ATOMIC_RELAXED		0
  #endif
  #ifndef __ATOMIC_CONSUME
  #define __ATOMIC_CONSUME		1
  #endif
  #ifndef __ATOMIC_ACQUIRE
  #define __ATOMIC_ACQUIRE		2
  #endif
  #ifndef __ATOMIC_RELEASE
  #define __ATOMIC_RELEASE		3
  #endif
  #ifndef __ATOMIC_ACQ_REL
  #define __ATOMIC_ACQ_REL		4
  #endif
  #ifndef __ATOMIC_SEQ_CST
  #define __ATOMIC_SEQ_CST		5
  #endif
  
  /*
   * 7.17.3 Order and consistency.
   *
   * The memory_order_* constants that denote the barrier behaviour of the
   * atomic operations.
   * The enum values must be identical to those used by the
   * C++ <atomic> header.
   */
  
  typedef enum {
  	memory_order_relaxed = __ATOMIC_RELAXED,
  	memory_order_consume = __ATOMIC_CONSUME,
  	memory_order_acquire = __ATOMIC_ACQUIRE,
  	memory_order_release = __ATOMIC_RELEASE,
  	memory_order_acq_rel = __ATOMIC_ACQ_REL,
  	memory_order_seq_cst = __ATOMIC_SEQ_CST
  } memory_order;
  
  /*
   * 7.17.4 Fences.
   */
  
  static __inline void
  atomic_thread_fence(memory_order __order __attribute__((unused)))
  {
  
  #ifdef __CLANG_ATOMICS
  	__c11_atomic_thread_fence(__order);
  #elif defined(__GNUC_ATOMICS)
  	__atomic_thread_fence(__order);
  #else
  	__sync_synchronize();
  #endif
  }
  
  static __inline void
  atomic_signal_fence(memory_order __order __attribute__((unused)))
  {
  
  #ifdef __CLANG_ATOMICS
  	__c11_atomic_signal_fence(__order);
  #elif defined(__GNUC_ATOMICS)
  	__atomic_signal_fence(__order);
  #else
  	__asm volatile ("" ::: "memory");
  #endif
  }
  
  /*
   * 7.17.5 Lock-free property.
   */
  
  #if defined(_KERNEL)
  /* Atomics in kernelspace are always lock-free. */
  #define	atomic_is_lock_free(obj) \
  	((void)(obj), (_Bool)1)
  #elif defined(__CLANG_ATOMICS)
  #define	atomic_is_lock_free(obj) \
  	__c11_atomic_is_lock_free(sizeof(*(obj)))
  #elif defined(__GNUC_ATOMICS)
  #define	atomic_is_lock_free(obj) \
  	__atomic_is_lock_free(sizeof((obj)->__val), &(obj)->__val)
  #else
  #define	atomic_is_lock_free(obj) \
  	((void)(obj), sizeof((obj)->__val) <= sizeof(void *))
  #endif
  
  /*
   * 7.17.6 Atomic integer types.
   */
  
  #ifndef __CLANG_ATOMICS
  /*
   * No native support for _Atomic(). Place object in structure to prevent
   * most forms of direct non-atomic access.
   */
  #define _Atomic(T)              struct { T volatile __val; }
  #endif
  
  typedef _Atomic(bool)			atomic_bool;
  typedef _Atomic(char)			atomic_char;
  typedef _Atomic(signed char)		atomic_schar;
  typedef _Atomic(unsigned char)		atomic_uchar;
  typedef _Atomic(short)			atomic_short;
  typedef _Atomic(unsigned short)		atomic_ushort;
  typedef _Atomic(int)			atomic_int;
  typedef _Atomic(unsigned int)		atomic_uint;
  typedef _Atomic(long)			atomic_long;
  typedef _Atomic(unsigned long)		atomic_ulong;
  typedef _Atomic(long long)		atomic_llong;
  typedef _Atomic(unsigned long long)	atomic_ullong;
  #if __STDC_VERSION__ >= 201112L || __cplusplus >= 201103L
    typedef _Atomic(char16_t)		atomic_char16_t;
    typedef _Atomic(char32_t)		atomic_char32_t;
  #endif
  typedef _Atomic(wchar_t)		atomic_wchar_t;
  typedef _Atomic(int_least8_t)		atomic_int_least8_t;
  typedef _Atomic(uint_least8_t)	atomic_uint_least8_t;
  typedef _Atomic(int_least16_t)	atomic_int_least16_t;
  typedef _Atomic(uint_least16_t)	atomic_uint_least16_t;
  typedef _Atomic(int_least32_t)	atomic_int_least32_t;
  typedef _Atomic(uint_least32_t)	atomic_uint_least32_t;
  typedef _Atomic(int_least64_t)	atomic_int_least64_t;
  typedef _Atomic(uint_least64_t)	atomic_uint_least64_t;
  typedef _Atomic(int_fast8_t)		atomic_int_fast8_t;
  typedef _Atomic(uint_fast8_t)		atomic_uint_fast8_t;
  typedef _Atomic(int_fast16_t)		atomic_int_fast16_t;
  typedef _Atomic(uint_fast16_t)	atomic_uint_fast16_t;
  typedef _Atomic(int_fast32_t)		atomic_int_fast32_t;
  typedef _Atomic(uint_fast32_t)	atomic_uint_fast32_t;
  typedef _Atomic(int_fast64_t)		atomic_int_fast64_t;
  typedef _Atomic(uint_fast64_t)	atomic_uint_fast64_t;
  typedef _Atomic(intptr_t)		atomic_intptr_t;
  typedef _Atomic(uintptr_t)		atomic_uintptr_t;
  typedef _Atomic(size_t)		atomic_size_t;
  typedef _Atomic(ptrdiff_t)		atomic_ptrdiff_t;
  typedef _Atomic(intmax_t)		atomic_intmax_t;
  typedef _Atomic(uintmax_t)		atomic_uintmax_t;
  
  /*
   * 7.17.7 Operations on atomic types.
   */
  
  /*
   * Compiler-specific operations.
   */
  
  #if defined(__CLANG_ATOMICS)
  #define	atomic_compare_exchange_strong_explicit(object, expected,	\
      desired, success, failure)						\
  	__c11_atomic_compare_exchange_strong(object, expected, desired,	\
  	    success, failure)
  #define	atomic_compare_exchange_weak_explicit(object, expected,		\
      desired, success, failure)						\
  	__c11_atomic_compare_exchange_weak(object, expected, desired,	\
  	    success, failure)
  #define	atomic_exchange_explicit(object, desired, order)		\
  	__c11_atomic_exchange(object, desired, order)
  #define	atomic_fetch_add_explicit(object, operand, order)		\
  	__c11_atomic_fetch_add(object, operand, order)
  #define	atomic_fetch_and_explicit(object, operand, order)		\
  	__c11_atomic_fetch_and(object, operand, order)
  #define	atomic_fetch_or_explicit(object, operand, order)		\
  	__c11_atomic_fetch_or(object, operand, order)
  #define	atomic_fetch_sub_explicit(object, operand, order)		\
  	__c11_atomic_fetch_sub(object, operand, order)
  #define	atomic_fetch_xor_explicit(object, operand, order)		\
  	__c11_atomic_fetch_xor(object, operand, order)
  #define	atomic_load_explicit(object, order)				\
  	__c11_atomic_load(object, order)
  #define	atomic_store_explicit(object, desired, order)			\
  	__c11_atomic_store(object, desired, order)
  #elif defined(__GNUC_ATOMICS)
  #define	atomic_compare_exchange_strong_explicit(object, expected,	\
      desired, success, failure)						\
  	__atomic_compare_exchange_n(&(object)->__val, expected,		\
  	    desired, 0, success, failure)
  #define	atomic_compare_exchange_weak_explicit(object, expected,		\
      desired, success, failure)						\
  	__atomic_compare_exchange_n(&(object)->__val, expected,		\
  	    desired, 1, success, failure)
  #define	atomic_exchange_explicit(object, desired, order)		\
  	__atomic_exchange_n(&(object)->__val, desired, order)
  #define	atomic_fetch_add_explicit(object, operand, order)		\
  	__atomic_fetch_add(&(object)->__val, operand, order)
  #define	atomic_fetch_and_explicit(object, operand, order)		\
  	__atomic_fetch_and(&(object)->__val, operand, order)
  #define	atomic_fetch_or_explicit(object, operand, order)		\
  	__atomic_fetch_or(&(object)->__val, operand, order)
  #define	atomic_fetch_sub_explicit(object, operand, order)		\
  	__atomic_fetch_sub(&(object)->__val, operand, order)
  #define	atomic_fetch_xor_explicit(object, operand, order)		\
  	__atomic_fetch_xor(&(object)->__val, operand, order)
  #define	atomic_load_explicit(object, order)				\
  	__atomic_load_n(&(object)->__val, order)
  #define	atomic_store_explicit(object, desired, order)			\
  	__atomic_store_n(&(object)->__val, desired, order)
  #else
  #define	__atomic_apply_stride(object, operand) \
  	(((__typeof__((object)->__val))0) + (operand))
  #define	atomic_compare_exchange_strong_explicit(object, expected,	\
      desired, success, failure)	__extension__ ({			\
  	__typeof__(expected) __ep = (expected);				\
  	__typeof__(*__ep) __e = *__ep;					\
  	(void)(success); (void)(failure);				\
  	(bool)((*__ep = __sync_val_compare_and_swap(&(object)->__val,	\
  	    __e, desired)) == __e);					\
  })
  #define	atomic_compare_exchange_weak_explicit(object, expected,		\
      desired, success, failure)						\
  	atomic_compare_exchange_strong_explicit(object, expected,	\
  		desired, success, failure)
  #ifdef __HAS_BUILTIN_SYNC_SWAP
  /* Clang provides a full-barrier atomic exchange - use it if available. */
  #define	atomic_exchange_explicit(object, desired, order)		\
  	((void)(order), __sync_swap(&(object)->__val, desired))
  #else
  /*
   * __sync_lock_test_and_set() is only an acquire barrier in theory (although in
   * practice it is usually a full barrier) so we need an explicit barrier before
   * it.
   */
  #define	atomic_exchange_explicit(object, desired, order)		\
  __extension__ ({							\
  	__typeof__(object) __o = (object);				\
  	__typeof__(desired) __d = (desired);				\
  	(void)(order);							\
  	__sync_synchronize();						\
  	__sync_lock_test_and_set(&(__o)->__val, __d);			\
  })
  #endif
  #define	atomic_fetch_add_explicit(object, operand, order)		\
  	((void)(order), __sync_fetch_and_add(&(object)->__val,		\
  	    __atomic_apply_stride(object, operand)))
  #define	atomic_fetch_and_explicit(object, operand, order)		\
  	((void)(order), __sync_fetch_and_and(&(object)->__val, operand))
  #define	atomic_fetch_or_explicit(object, operand, order)		\
  	((void)(order), __sync_fetch_and_or(&(object)->__val, operand))
  #define	atomic_fetch_sub_explicit(object, operand, order)		\
  	((void)(order), __sync_fetch_and_sub(&(object)->__val,		\
  	    __atomic_apply_stride(object, operand)))
  #define	atomic_fetch_xor_explicit(object, operand, order)		\
  	((void)(order), __sync_fetch_and_xor(&(object)->__val, operand))
  #define	atomic_load_explicit(object, order)				\
  	((void)(order), __sync_fetch_and_add(&(object)->__val, 0))
  #define	atomic_store_explicit(object, desired, order)			\
  	((void)atomic_exchange_explicit(object, desired, order))
  #endif
  
  /*
   * Convenience functions.
   *
   * Don't provide these in kernel space. In kernel space, we should be
   * disciplined enough to always provide explicit barriers.
   */
  
  #ifndef _KERNEL
  #define	atomic_compare_exchange_strong(object, expected, desired)	\
  	atomic_compare_exchange_strong_explicit(object, expected,	\
  	    desired, memory_order_seq_cst, memory_order_seq_cst)
  #define	atomic_compare_exchange_weak(object, expected, desired)		\
  	atomic_compare_exchange_weak_explicit(object, expected,		\
  	    desired, memory_order_seq_cst, memory_order_seq_cst)
  #define	atomic_exchange(object, desired)				\
  	atomic_exchange_explicit(object, desired, memory_order_seq_cst)
  #define	atomic_fetch_add(object, operand)				\
  	atomic_fetch_add_explicit(object, operand, memory_order_seq_cst)
  #define	atomic_fetch_and(object, operand)				\
  	atomic_fetch_and_explicit(object, operand, memory_order_seq_cst)
  #define	atomic_fetch_or(object, operand)				\
  	atomic_fetch_or_explicit(object, operand, memory_order_seq_cst)
  #define	atomic_fetch_sub(object, operand)				\
  	atomic_fetch_sub_explicit(object, operand, memory_order_seq_cst)
  #define	atomic_fetch_xor(object, operand)				\
  	atomic_fetch_xor_explicit(object, operand, memory_order_seq_cst)
  #define	atomic_load(object)						\
  	atomic_load_explicit(object, memory_order_seq_cst)
  #define	atomic_store(object, desired)					\
  	atomic_store_explicit(object, desired, memory_order_seq_cst)
  #endif /* !_KERNEL */
  
  /*
   * 7.17.8 Atomic flag type and operations.
   *
   * XXX: Assume atomic_bool can be used as an atomic_flag. Is there some
   * kind of compiler built-in type we could use?
   */
  
  typedef struct {
  	atomic_bool	__flag;
  } atomic_flag;
  
  #define	ATOMIC_FLAG_INIT		{ ATOMIC_VAR_INIT(false) }
  
  static __inline bool
  atomic_flag_test_and_set_explicit(volatile atomic_flag *__object,
      memory_order __order)
  {
  	return (atomic_exchange_explicit(&__object->__flag, 1, __order));
  }
  
  static __inline void
  atomic_flag_clear_explicit(volatile atomic_flag *__object, memory_order __order)
  {
  
  	atomic_store_explicit(&__object->__flag, 0, __order);
  }
  
  #ifndef _KERNEL
  static __inline bool
  atomic_flag_test_and_set(volatile atomic_flag *__object)
  {
  
  	return (atomic_flag_test_and_set_explicit(__object,
  	    memory_order_seq_cst));
  }
  
  static __inline void
  atomic_flag_clear(volatile atomic_flag *__object)
  {
  
  	atomic_flag_clear_explicit(__object, memory_order_seq_cst);
  }
  #endif /* !_KERNEL */
  
  #endif /* <atomic> unavailable */
  
  #endif /* !_STDATOMIC_H_ */
  