static byte[] subByteArray(byte[] b, int start) {
  ret subByteArray(b, start, l(b));
}
  
static byte[] subByteArray(byte[] b, int start, int end) {
  start = max(start, 0); end = min(end, l(b));
  if (start == 0 && end == l(b)) ret b;
  if (start >= end) ret new byte[0];
  byte[] x = new byte[end-start];
  System.arraycopy(b, start, x, 0, end-start);
  ret x;
}

ifclass IntRange
static byte[] subByteArray(byte[] b, IntRange r) {
  ret r == null ?: subByteArray(b, r.start, r.end);
}
endif