Three implementations of the memmove function in C language freeBSD

I am making my own memmove while looking at the implementation of memmove in freeBSD. Multiple memmove functions were defined.

I thought that the same coding standard was applied to all of freeBSD, but it was interesting because of the variation in writing style, so I will leave it as a memo.

freebsd/freebsd: FreeBSD src tree (read-only mirror)

sys/contrib/xz-embedded/linux/lib/decompress_unxz.c

void *memmove(void *dest, const void *src, size_t size)
{
	uint8_t *d = dest;
	const uint8_t *s = src;
	size_t i;

	if (d < s) {
		for (i = 0; i < size; ++i)
			d[i] = s[i];
	} else if (d > s) {
		i = size;
		while (i-- > 0)
			d[i] = s[i];
	}

	return dest;
}

crypto/heimdal/lib/roken/memmove.c

ROKEN_LIB_FUNCTION void* ROKEN_LIB_CALL
memmove(void *s1, const void *s2, size_t n)
{
  char *s=(char*)s2, *d=(char*)s1;

  if(d > s){
    s+=n-1;
    d+=n-1;
    while(n){
      *d--=*s--;
      n--;
    }
  }else if(d < s)
    while(n){
      *d++=*s++;
      n--;
    }
  return s1;
}

contrib/unbound/compat/memmove.c

void *memmove(void *dest, const void *src, size_t n)
{
	uint8_t* from = (uint8_t*) src;
	uint8_t* to = (uint8_t*) dest;

	if (from == to || n == 0)
		return dest;
	if (to > from && to-from < (int)n) {
		/* to overlaps with from */
		/*  <from......>         */
		/*         <to........>  */
		/* copy in reverse, to avoid overwriting from */
		int i;
		for(i=n-1; i>=0; i--)
			to[i] = from[i];
		return dest;
	}
	if (from > to && from-to < (int)n) {
		/* to overlaps with from */
		/*        <from......>   */
		/*  <to........>         */
		/* copy forwards, to avoid overwriting from */
		size_t i;
		for(i=0; i<n; i++)
			to[i] = from[i];
		return dest;
	}
	memcpy(dest, src, n);
	return dest;
}