static int[] subIntArray(int[] b, int start) {
  ret subIntArray(b, start, l(b));
}
  
static int[] subIntArray(int[] 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 int[0];
  int[] x = new int[end-start];
  System.arraycopy(b, start, x, 0, end-start);
  ret x;
}

ifclass IntRange
static int[] subIntArray(int[] a, IntRange r) {
  ret r == null ? null : subIntArray(a, r.start, r.end);
}
endif

Began life as a copy of #1014874