static S extractLastNLinesOfString(int n, S s) {
  int i = l(s)-1;
  // skip trailing new line
  if (i >= 0 && s.charAt(i) == '\n') --i;
  if (i >= 0 && s.charAt(i) == '\r') --i;
  
  while (n > 0 && i >= 0) {
    if (s.charAt(i) == '\n')
      if (--n == 0) break;
    --i;
  }

  ret substring(s, i+1);
}
  
static S extractLastNLinesOfString(S s, int n) {
  ret extractLastNLinesOfString(n, s);
}

Began life as a copy of #1004746