内存拷贝函数 memcpy

windows下实现：

void* __cdecl memcpy(void* dst,const void* src,size_t count)
{
    void*ret=dst;
　　#if defined(_M_MRX000)||defined(_M_ALPHA)||defined(_M_PPC)
　　{
   　　  extern void RtlMoveMemory(void *,const void *,size_t count);
    　　 RtlMoveMemory(dst,src,count);
　　}
　　#else /*defined(_M_MRX000)||defined(_M_ALPHA)||defined(_M_PPC)*/
　　/*
　　*copy from lower addresses to higher addresses
　　*/
　　while(count--){
  　　  *(char *)dst = *(char *)src;
   　　 dst = (char *)dst+1;
   　　 src = (char *)src+1;
　　}
　　#endif  /*defined(_M_MRX000)||defined(_M_ALPHA)||defined(_M_PPC)*/
　　return (ret);
}

liunx下实现的代码：

void *memcpy(void *to, const void *from, size_t n)
{
　　 //记录拷贝目的位置，为了返回拷贝内容的首地址
    void *xto = to;
    size_t temp, temp1;
 　
　　 //判断拷贝的字节数
    if (!n)
        return xto;
　　 //
    if ((long)to & 1) {
        char *cto = to;
        const char *cfrom = from;
        *cto++ = *cfrom++;
        to = cto;
        from = cfrom;
        n--;
    }
    if (n > 2 && (long)to & 2) {
        short *sto = to;
        const short *sfrom = from;
        *sto++ = *sfrom++;
        to = sto;
        from = sfrom;
        n -= 2;
    }
    temp = n >> 2;
    if (temp) {
        long *lto = to;
        const long *lfrom = from;
　　#if defined(CONFIG_M68000) || defined(CONFIG_COLDFIRE)
        for (; temp; temp--)
            *lto++ = *lfrom++;
　　#else
        asm volatile (
            "    movel %2,%3\n"
            "    andw  #7,%3\n"
            "    lsrl  #3,%2\n"
            "    negw  %3\n"
            "    jmp   %%pc@(1f,%3:w:2)\n"
            "4:    movel %0@+,%1@+\n"
            "    movel %0@+,%1@+\n"
            "    movel %0@+,%1@+\n"
            "    movel %0@+,%1@+\n"
            "    movel %0@+,%1@+\n"
            "    movel %0@+,%1@+\n"
            "    movel %0@+,%1@+\n"
            "    movel %0@+,%1@+\n"
            "1:    dbra  %2,4b\n"
            "    clrw  %2\n"
            "    subql #1,%2\n"
            "    jpl   4b"
            : "=a" (lfrom), "=a" (lto), "=d" (temp), "=&d" (temp1)
            : "0" (lfrom), "1" (lto), "2" (temp));
　　#endif
        to = lto;
        from = lfrom;
   　　 }
   　　if (n & 2) {
        short *sto = to;
        const short *sfrom = from;
        *sto++ = *sfrom++;
        to = sto;
        from = sfrom;
    　　}
   　　 if (n & 1) {
       　　 char *cto = to;
       　　 const char *cfrom = from;
      　　  *cto = *cfrom;
  　　  }
    return xto;
}