内存拷贝函数

武汉小锋

于 2010-06-07 11:13:00 发布

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分类专栏： Algorithm Practice 文章标签： dst

本文链接：https://blog.youkuaiyun.com/woshipangxiaofeng/article/details/5652514

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void* memcpy( void *dst, const void *src, unsigned int len )
{
register char *d;
register char *s;
if (len == 0)
      return dst;
if ( dst > src ) //考虑覆盖情况
{
      d = (char *)dst + len - 1;
      s = (char *)src + len - 1;
      while ( len >= 4 ) //循环展开，提高执行效率
      {
         *d-- = *s--;
         *d-- = *s--;
         *d-- = *s--;
         *d-- = *s--;
         len -= 4;
      }
      while ( len-- )
      {
         *d-- = *s--;
      }
}
else if ( dst < src )
{
      d = (char *)dst;
      s = (char *)src;
      while ( len >= 4 )
      {
         *d++ = *s++;
         *d++ = *s++;
         *d++ = *s++;
         *d++ = *s++;
         len -= 4;
      }
      while ( len-- )
      {
         *d++ = *s++;
      }
}
return dst;
}