FreeBSD/Linux Kernel Cross Reference
sys/include/asm-alpha/atomic.h

     #ifndef _ALPHA_ATOMIC_H
     #define _ALPHA_ATOMIC_H
     
     /*
      * Atomic operations that C can't guarantee us.  Useful for
      * resource counting etc...
      *
      * But use these as seldom as possible since they are much slower
      * than regular operations.
     */
    
    
    /*
     * Counter is volatile to 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)  ( (atomic_t) { (i) } )
    
    #define atomic_read(v)          ((v)->counter)
    #define atomic_set(v,i)         ((v)->counter = (i))
    
    /*
     * To get proper branch prediction for the main line, we must branch
     * forward to code at the end of this object's .text section, then
     * branch back to restart the operation.
     */
    
    static __inline__ void atomic_add(int i, atomic_t * v)
    {
            unsigned long temp;
            __asm__ __volatile__(
            "1:     ldl_l %0,%1\n"
            "       addl %0,%2,%0\n"
            "       stl_c %0,%1\n"
            "       beq %0,2f\n"
            ".subsection 2\n"
            "2:     br 1b\n"
            ".previous"
            :"=&r" (temp), "=m" (v->counter)
            :"Ir" (i), "m" (v->counter));
    }
    
    static __inline__ void atomic_sub(int i, atomic_t * v)
    {
            unsigned long temp;
            __asm__ __volatile__(
            "1:     ldl_l %0,%1\n"
            "       subl %0,%2,%0\n"
            "       stl_c %0,%1\n"
            "       beq %0,2f\n"
            ".subsection 2\n"
            "2:     br 1b\n"
            ".previous"
            :"=&r" (temp), "=m" (v->counter)
            :"Ir" (i), "m" (v->counter));
    }
    
    /*
     * Same as above, but return the result value
     */
    static __inline__ long atomic_add_return(int i, atomic_t * v)
    {
            long temp, result;
            __asm__ __volatile__(
            "1:     ldl_l %0,%1\n"
            "       addl %0,%3,%2\n"
            "       addl %0,%3,%0\n"
            "       stl_c %0,%1\n"
            "       beq %0,2f\n"
            "       mb\n"
            ".subsection 2\n"
            "2:     br 1b\n"
            ".previous"
            :"=&r" (temp), "=m" (v->counter), "=&r" (result)
            :"Ir" (i), "m" (v->counter) : "memory");
            return result;
    }
    
    static __inline__ long atomic_sub_return(int i, atomic_t * v)
    {
            long temp, result;
            __asm__ __volatile__(
            "1:     ldl_l %0,%1\n"
            "       subl %0,%3,%2\n"
            "       subl %0,%3,%0\n"
            "       stl_c %0,%1\n"
            "       beq %0,2f\n"
            "       mb\n"
            ".subsection 2\n"
            "2:     br 1b\n"
            ".previous"
            :"=&r" (temp), "=m" (v->counter), "=&r" (result)
            :"Ir" (i), "m" (v->counter) : "memory");
            return result;
    }
    
   #define atomic_dec_return(v) atomic_sub_return(1,(v))
   #define atomic_inc_return(v) atomic_add_return(1,(v))
   
   #define atomic_sub_and_test(i,v) (atomic_sub_return((i), (v)) == 0)
   #define atomic_dec_and_test(v) (atomic_sub_return(1, (v)) == 0)
   
   #define atomic_inc(v) atomic_add(1,(v))
   #define atomic_dec(v) atomic_sub(1,(v))
   
   #define smp_mb__before_atomic_dec()     smp_mb()
   #define smp_mb__after_atomic_dec()      smp_mb()
   #define smp_mb__before_atomic_inc()     smp_mb()
   #define smp_mb__after_atomic_inc()      smp_mb()
   
   #endif /* _ALPHA_ATOMIC_H */

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