scope intersectSortedIntArrays.

// may return null when result is empty
static int[] intersectSortedIntArrays(int[] a, int[] b, IntBuffer buf default null) {
  int i = 0, j = 0, la = lIntArray(a), lb = lIntArray(b);
  
  // swap if a is longer than b
  if (la > lb) {
    int[] temp = a; a = b; b = temp;
    int temp2 = la; la = lb; lb = temp2;
  }
  
  // special case zero elements
  if (la == 0) null;
  
  // special case one element
  if (la == 1)
    ret Arrays.binarySearch(b, a[0]) >= 0 ? a : null;
    
  if (buf == null) buf = new IntBuffer; else buf.reset();
  recurse(a, b, buf, 0, la, 0, lb);
  ret buf.toArray();
}

svoid #recurse(int[] a, int[] b, IntBuffer buf, int aFrom, int aTo, int bFrom, int bTo) {
  if (aFrom >= aTo || bFrom >= bTo) ret; // nothing to do
  
  // start in the middle of a, search this element in b
  int i = (aFrom+aTo)/2;
  int x = a[i];
  int j = Arrays.binarySearch(b, bFrom, bTo, x);

  if (j >= 0) {
    // element found
    recurse(a, b, buf, aFrom, i, bFrom, j);
    buf.add(x);
    recurse(a, b, buf, i+1, aTo, j+1, bTo);
  } else {
    j = -j-1;
    recurse(a, b, buf, aFrom, i, bFrom, j);
    recurse(a, b, buf, i+1, aTo, j, bTo);
  }
}

end scope

Began life as a copy of #1029031