atomic.h

// The "atomic.h" file provides low-level atomic memory primitives for the
// x86 plattform. All functions in this file provide sequential memory
// consistency.


// atomic_load atomically loads *addr.
static inline int atomic_load(int *addr)
{
	int val = *(volatile const int*)(addr);
	__asm__ __volatile__ ("" ::: "memory");
	return val;
}

// atomic_store atomically stores val into *addr.
static inline void atomic_store(int *addr, int val)
{
	__asm__ __volatile__ (
		"xchgl %0, %1\n" :
		"=q" (val) :
		"m" (*addr), "0" (val) :
		"memory");
}

// atomic_add atomically adds delta to *addr and returns the new value.
static inline int atomic_add(int *addr, int delta)
{
	int t = delta;
	__asm__ __volatile__ (
		"lock; xaddl %0, %1" :
		"+q" (delta), "+m" (*addr) :
		:
		"memory");
	return delta + t;
}

// atomic_cas executes the compare-and-swap operation on *addr.
static inline int atomic_cas(int *addr, int expected, int desired)
{
	__asm__ __volatile__ ("" ::: "memory");
	int prev = expected;
	__asm__ __volatile__ (
		"lock; cmpxchgl %1, %2\n" :
		"=a" (prev) :
		"q" (desired), "m" (*addr), "a" (expected) :
		"memory");
	int success = (prev == expected);
	__asm__ __volatile__ ("" ::: "memory");
	return success;
}