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+;

   　　 src = (char *)src+;

　　}

　　#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 & ) {

        char *cto = to;

        const char *cfrom = from;

        *cto++ = *cfrom++;

        to = cto;

        from = cfrom;

        n--;

    }

    if (n >  && (long)to & ) {

        short *sto = to;

        const short *sfrom = from;

        *sto++ = *sfrom++;

        to = sto;

        from = sfrom;

        n -= ;

    }

    temp = n >> ;

    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)

            : "" (lfrom), "" (lto), "" (temp));

　　#endif

        to = lto;

        from = lfrom;

   　　 }

   　　if (n & ) {

        short *sto = to;

        const short *sfrom = from;

        *sto++ = *sfrom++;

        to = sto;

        from = sfrom;

    　　}

   　　 if (n & ) {

       　　 char *cto = to;

       　　 const char *cfrom = from;

      　　  *cto = *cfrom;

  　　  }

    return xto;

}