atomic.h

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#ifndef ATOMIC_H
#define ATOMIC_H

/*
 * Atomic operations that C can't guarantee us.  Useful for
 * resource counting etc..
 */

#define LOCK "lock ; "

/*
 * Make sure gcc doesn't try to be clever and move things around
 * on us. We need to use _exactly_ the address the user gave us,
 * not some alias that contains the same information.
 */
typedef struct { volatile int counter; } atomic_t;

#define ATOMIC_INIT(i)  { (i) }

#define atomic_read(v)          ((v)->counter)

#define atomic_set(v,i)         (((v)->counter) = (i))

static __inline__ void atomic_add(int i, atomic_t *v)
{
        __asm__ __volatile__(
                LOCK "addl %1,%0"
                :"=m" (v->counter)
                :"ir" (i), "m" (v->counter));
}

static __inline__ void atomic_sub(int i, atomic_t *v)
{
        __asm__ __volatile__(
                LOCK "subl %1,%0"
                :"=m" (v->counter)
                :"ir" (i), "m" (v->counter));
}


static __inline__ int atomic_add_return(int i, atomic_t *v)
{
  int __i;
  /* Modern 486+ processor */
  __i = i;
  __asm__ __volatile__(
                LOCK "xaddl %0, %1"
                :"+r" (i), "+m" (v->counter)
                : : "memory");
  return i + __i;
}

static __inline__ int atomic_sub_return(int i, atomic_t *v)
{
  return atomic_add_return(-i,v);
}


static __inline__ int atomic_sub_and_test(int i, atomic_t *v)
{
        unsigned char c;

        __asm__ __volatile__(
                LOCK "subl %2,%0; sete %1"
                :"=m" (v->counter), "=qm" (c)
                :"ir" (i), "m" (v->counter) : "memory");
        return c;
}

static __inline__ void atomic_inc(atomic_t *v)
{
        __asm__ __volatile__(
                LOCK "incl %0"
                :"=m" (v->counter)
                :"m" (v->counter));
}

static __inline__ void atomic_dec(atomic_t *v)
{
        __asm__ __volatile__(
                LOCK "decl %0"
                :"=m" (v->counter)
                :"m" (v->counter));
}

static __inline__ int atomic_dec_and_test(atomic_t *v)
{
        unsigned char c;

        __asm__ __volatile__(
                LOCK "decl %0; sete %1"
                :"=m" (v->counter), "=qm" (c)
                :"m" (v->counter) : "memory");
        return c != 0;
}

static __inline__ int atomic_inc_and_test(atomic_t *v)
{
        unsigned char c;

        __asm__ __volatile__(
                LOCK "incl %0; sete %1"
                :"=m" (v->counter), "=qm" (c)
                :"m" (v->counter) : "memory");
        return c != 0;
}

static __inline__ int atomic_add_negative(int i, atomic_t *v)
{
        unsigned char c;

        __asm__ __volatile__(
                LOCK "addl %2,%0; sets %1"
                :"=m" (v->counter), "=qm" (c)
                :"ir" (i), "m" (v->counter) : "memory");
        return c;
}

/* These are x86-specific, used by some header files */
#define atomic_clear_mask(mask, addr) \
__asm__ __volatile__(LOCK "andl %0,%1" \
: : "r" (~(mask)),"m" (*addr) : "memory")

#define atomic_set_mask(mask, addr) \
__asm__ __volatile__(LOCK "orl %0,%1" \
: : "r" (mask),"m" (*(addr)) : "memory")

#define atomic_inc_return(v)  (atomic_add_return(1,v))
#define atomic_dec_return(v)  (atomic_sub_return(1,v))

#endif // ATOMIC_H