Fast strncpy

This is fast strncpy implementation a-lГ  Duff's device:

 void * dps_strncpy(void *dst0, const void *src0, size_t length) {
if (length) {
register size_t n = (length + 7) / 8;
register char *dst = dst0, *src = src0;
switch(length % 8 ) {
case 0:    do {    if (!(*dst++ = *src++)) break;
case 7:        if (!(*dst++ = *src++)) break;
case 6:        if (!(*dst++ = *src++)) break;
case 5:        if (!(*dst++ = *src++)) break;
case 4:        if (!(*dst++ = *src++)) break;
case 3:        if (!(*dst++ = *src++)) break;
case 2:        if (!(*dst++ = *src++)) break;
case 1:        if (!(*dst++ = *src++)) break;
} while(--n > 0);
}
}
return dst0;
} 

N.B.: code is under GPL.