shorter fmt_ulong

On my box DJB fmt_ulong is shorter than included in libowfat.
Here I suggest one fmt_ulong which is even shorter than DJB fmt_ulong.
I doesn't compare them for speed.  Which is better for fmt_ulong:
short or fast? 

Felix, I have send already one improvement for sysconf.  It uses
sysinfo(2) to get physical RAM instead of parsing /proc/... files.
Have you seen it already?

Nikola
#include <sys/types.h>

size_t fmt_ulong(char *s, unsigned long u) {
  size_t len; unsigned long q;
  len = 0; q = u;
  do { ++len; q /= 10; } while (q);
  if (s) {
    s += len;
    do { *--s = '0' + (u % 10); u /= 10; } while(u); /* handles u == 0 */
  }
  return len;
}