Fast memcpy implementation

Rate this post


void * dps_memcpy(void *dst0, const void *src0, size_t length) {

  if (length == 0 || dst0 == src0)		/* nothing to do */
    return dst0;
  if ((unsigned long)dst0 < (unsigned long)src0) { /* copy forward */
    register size_t n = (length + 7) / 8;
    register char *dst = dst0, *src = src0;
    switch( length % 8 ) {
    case 0:	do {	*dst++ = *src++;
    case 7:		*dst++ = *src++;
    case 6:		*dst++ = *src++;
    case 5:		*dst++ = *src++;
    case 4:		*dst++ = *src++;
    case 3:		*dst++ = *src++;
    case 2:		*dst++ = *src++;
    case 1:		*dst++ = *src++;
                    } while(--n > 0);
    }
  } else { /* copy backward */
    register size_t n = (length + 7) / 8;
    register char *dst = dst0 + length, *src = src0 + length;
    switch( length % 8 ) {
    case 0:	do {	*--dst = *--src;
    case 7:		*--dst = *--src;
    case 6:		*--dst = *--src;
    case 5:		*--dst = *--src;
    case 4:		*--dst = *--src;
    case 3:		*--dst = *--src;
    case 2:		*--dst = *--src;
    case 1:		*--dst = *--src;
                    } while(--n > 0);
    }
  }
  return dst0;
}

N.B.: Code is under GPL.

Addendum: A faster version of memcpy

5 thoughts on “Fast memcpy implementation

  1. Jan

    That's not fast. In fact it's more than three times slower than my implementations (plain C). Anything that is not accidently char *s, *d; while(n--) *d++ = *s++ can possibly already beat this.

  2. Divya

    Could you tell me how your implementation looks like? And by saying its faster, is it faster that whats natively available in gcc or just faster than the routine given here?

  3. Pingback: Even faster memcpy | Founds

Leave a Reply

Your email address will not be published. Required fields are marked *