Function check

src/sort.c:3069–3148

   they are not in order.  */

static bool
check (char const *file_name, char checkonly)
{
  FILE *fp = xfopen (file_name, "r");
  struct buffer buf;		/* Input buffer. */
  struct line temp;		/* Copy of previous line. */
  size_t alloc = 0;
  uintmax_t line_number = 0;
  struct keyfield const *key = keylist;
  bool nonunique = ! unique;
  bool ordered = true;

  initbuf (&buf, sizeof (struct line),
           MAX (merge_buffer_size, sort_size));
  temp.text = NULL;

  while (fillbuf (&buf, fp, file_name))
    {
      struct line const *line = buffer_linelim (&buf);
      struct line const *linebase = line - buf.nlines;

      /* Make sure the line saved from the old buffer contents is
         less than or equal to the first line of the new buffer. */
      if (alloc && nonunique <= compare (&temp, line - 1))
        {
        found_disorder:
          {
            if (checkonly == 'c')
              {
                struct line const *disorder_line = line - 1;
                uintmax_t disorder_line_number =
                  buffer_linelim (&buf) - disorder_line + line_number;
                fprintf (stderr, _("%s: %s:%ju: disorder: "),
                         program_name, file_name, disorder_line_number);
                write_line (disorder_line, stderr, _("standard error"));
              }

            ordered = false;
            break;
          }
        }

      /* Compare each line in the buffer with its successor.  */
      while (linebase < --line)
        if (nonunique <= compare (line, line - 1))
          goto found_disorder;

      line_number += buf.nlines;

      /* Save the last line of the buffer.  */
      if (alloc < line->length)
        {
          do
            {
              alloc *= 2;
              if (! alloc)
                {
                  alloc = line->length;