random() in pure sh

random() {
  local n x
  if [ $1 -le 0 ]; then
    echo 0
    return
  fi
  if [ $1 -lt 255 ]; then
    n=1
  elif [ $1 -lt 65535 ]; then
    n=2
  else
    n=4
  fi
  x='0x'$(dd if=/dev/urandom bs=$n count=1 2>/dev/null | xxd -ps)
  echo $((x % $1))
}