实现 PowerPC 下的原子操作

@File: atomic.asm

;;; u32_t atomic_modify(u32_t *addr, u32_t mask, u32_t delta);
;;; @param [r3]: addr
;;; @param [r4]: mask
;;; @param [r5]: delta
;;; @return [r3]: the old value
.global atomic_modify
atomic_modify:
        lwarx   r6,0,r3
        andc    r7,r6,r4
        add     r7,r7,r5
        stwcx.  r7,0,r3
        bne+    atomic_modify
        mr      r3,r6
        blr

@File: atomic.h

#ifndef LIBCOMMON_ATOMIC_H
#define LIBCOMMON_ATOMIC_H

unsigned int atomic_modify(unsigned int *addr, unsigned int mask, unsigned int delta);

inline unsigned int atomic_decrement(unsigned int *pval)
{
    return atomic_modify(pval, 0, ~(unsigned int)0);
}

inline unsigned int atomic_increment(unsigned int *pval)
{
    return atomic_modify(pval, 0, 1);    
}

inline unsigned int atomic_read(unsigned int *pval)
{
    return atomic_modify(pval, 0, 0);
}

inline unsigned int atomic_write(unsigned int *pval, unsigned int val)
{
    return atomic_modify(pval, ~(unsigned int)0, val);
}

#endif