菜菜CPP日记

分支预测建议：

http://www.cppblog.com/mysileng/archive/2014/09/29/208454.html

#ifndef likely
#define likely(x)                   __builtin_expect(!!(x), 1)
#endif
#ifndef unlikely
#define unlikely(x)                 __builtin_expect(!!(x), 0)
#endif

内存对齐：

这个表达式的意思就是 d/a 向上取整(a是2的倍数)。也就是说 如果表达式的结果是n那么
(n - 1) *a<d <= n * a，
如果按a对齐那么至少要申请n这么大才能把d放里面。

#define align_ptr(p, a)        (uint8_t*)(((uintptr_t)(p) + ((uintptr_t) a - 1)) & ~((uintptr_t) a - 1))
#define align(d, a)            (((d) + (a - 1)) & ~(a - 1))

属性暗示：

http://www.cnblogs.com/sunyubo/archive/2010/12/20/2282084.html

#define ignore(exp)            {int ignore __attribute__ ((unused)) = (exp);}

// 内存对齐
struct my_unpacked_struct
{
char c;
int i;
};
struct my_packed_struct
{
char c;
int i;
struct my_unpacked_struct s;

}__attribute__ ((__packed__));

汇编与锁：

http://blog.csdn.net/lu_ming/article/details/4984115

http://blog.csdn.net/maotianwang/article/details/9154159

/ 32位系统
static __inline__ void atomic32_add(volatile int32_t *v, int i) {
__asm__ __volatile__("lock;" "addl %1,%0"
        : "=m" ((*v)) : "r" (i), "m" ((*v)));
}
static __inline__ int32_t atomic32_add_return(volatile int32_t *value, int32_t diff)
{
    int32_t                 old = diff;
    __asm__ volatile (
        "lock;" "xaddl %0, %1"
        :"+r" (diff), "+m" (*value) : : "memory");
    return diff + old;
}
static __inline__ void atomic32_inc(volatile int32_t *value *v)
{
    __asm__ __volatile__("lock;" "incl %0" : "=m" (*v) :"m" (*v));
}
static __inline__ void atomic32_dec(volatile int32_t *value*v)
{
    __asm__ __volatile__("lock;" "decl %0" : "=m" (*v) :"m" (*v));
}
static __inline__ int32_t atomic_cmp_set(volatile int32_t *lock, int32_t old, int32_t set)
{
    uint8_t res;
    __asm__ volatile (
        "lock;" "cmpxchgl %3, %1; sete %0"
        : "=a" (res) : "m" (*lock), "a" (old), "r" (set) : "cc", "memory");
    return res;
}
//
#define trylock(lock) (*(lock) == 0 && atomic_cmp_set(lock, 0, 1))
#define unlock(lock) {__asm__ ("" ::: "memory"); *(lock) = 0;}
// 自旋lock
static __inline__ void spin_lock(volatile int32_t *lock)
{
　　int i,n;
   for(;;) {
     if(*lock == 0 && atomic_cmp_set(lock, 0, 1)) {
       return;
　　 }

     for(n = 1; n < 1024; n <<= 1) {
       for(i = 0; i < n; i++) {
         __asm__ (".byte 0xf3, 0x90");
       }

       if(*lock == 0 && atomic_cmp_set(lock, 0, 1)) {
         return;
　    }
    }
   }
   //?? sched_yield();
}
#define spin_unlock unlock