c - Aligning both source and destination address in memcpy -

i want write memcpy code word word copy instead of byte byte increase speed. (though need byte byte copy last or few bytes). want source , destination address aligned properly. saw implementation of memcpy in glibc https://fossies.org/dox/glibc-2.22/string_2memcpy_8c_source.html alignment destination address. if source address not aligned result bus error (consider alignment checking enabled in cpu) i'm not sure how make both source , destination aligned properly. because if try align source copying few bytes byte byte, change destination address, @ first destination address aligned @ first might not aligned now. there way align both?. please me.

void  memcpy(void  *dst,  void  *src,int  size) {    if(size >= 8)    {      while(size/8) /* code give sigbus error if src = 0x10003 , dst = 0x100000 */       {        *((double*)dst)++  =  *((double*)src)++;          size  =  size  -  8;      }    }     while(size--)    {      *((char*)dst)++  =  *((char*)src)++;    } } 

...so @ first destination address aligned @ first might not aligned now. there way align both?

i found article on memcpy optimization believe discusses trying in length... (see link below code example)

modified-gnu algorithm:

void * memcpy(void * dst, void const * src, size_t len) {     long * pldst = (long *) dst;     long const * plsrc = (long const *) src;      if (!(src & 0xfffffffc) && !(dst & 0xfffffffc))     {         while (len >= 4)     {             *pldst++ = *plsrc++;             len -= 4;         }     }      char * pcdst = (char *) pldst;     char const * pcdst = (char const *) plsrc;      while (len--)     {         *pcdst++ = *pcsrc++;     }      return (dst); }  

this variation of modified-gnu algorithm uses computation adjust address misalignment.