linux memcpy 독특하게 구현돼있네요.. 이유가 뭘까요?

char* memcpy(char* dest, char* src, int size)
{
	int i = 0;
	unsigned char *d = (unsigned char *)dest, *s = (unsigned char *)src;
 
	for (i = size >> 3; i > 0; i--) {
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
	}
 
	if (size & 1 << 2) {
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
		*d++ = *s++;
	}
 
	if (size & 1 << 1) {
		*d++ = *s++;
		*d++ = *s++;
	}
 
	if (size & 1)
		*d++ = *s++;
 
	return dest;
}