/* Close out an extent.  Must be called with valid cf values */
static void
trunc_cf(CFILE *cf)
{
    long pos = cf->pos;
    int lex;
    int rc;

    if (cf->dirp < 0)
	return;

    /*
     * cf->pos points one byte past the last byte written/copied.
     * If the file length is exactly on a 16 KiB logical-extent boundary,
     * the last valid extent is the previous one and its record count is
     * 0x80.  The old calculation used pos/(16*1024) and masked the record
     * count with 0x7f; for 16/32/48 KiB files this changed the previous
     * directory entry to the next extent and wrote RC=0.
     */
    if (pos > 0 && (pos & 0x3fff) == 0) {
	lex = (pos - 1) / (16*1024);
	rc = 0x80;
    }
    else {
	lex = pos / (16*1024);
	rc = ((pos & 0x3fff) + 127) >> 7;
    }

    {
	BYTE *entry = cf->dp->dir + cf->dirp*32;
	entry[12] = lex&0x1f;
	entry[14] = lex>>5;
	entry[15] = rc;
    }
}