/* [MS-CFB] 2.2 Compound File Header -- read up to major version */
function check_get_mver(blob/*:CFBlob*/)/*:[number, number]*/ {
	if(blob[blob.l] == 0x50 && blob[blob.l + 1] == 0x4b) return [0, 0];
	// header signature 8
	blob.chk(HEADER_SIGNATURE, 'Header Signature: ');

	// clsid 16
	blob.chk(HEADER_CLSID, 'CLSID: ');

	// minor version 2
	var mver/*:number*/ = blob.read_shift(2, 'u');

	return [blob.read_shift(2,'u'), mver];
}
function check_shifts(blob/*:CFBlob*/, mver/*:number*/)/*:void*/ {
	var shift = 0x09;

	// Byte Order
	//blob.chk('feff', 'Byte Order: '); // note: some writers put 0xffff
	blob.l += 2;

	// Sector Shift
	switch((shift = blob.read_shift(2))) {
		case 0x09: if(mver != 3) throw new Error('Sector Shift: Expected 9 saw ' + shift); break;
		case 0x0c: if(mver != 4) throw new Error('Sector Shift: Expected 12 saw ' + shift); break;
		default: throw new Error('Sector Shift: Expected 9 or 12 saw ' + shift);
	}

	// Mini Sector Shift
	blob.chk('0600', 'Mini Sector Shift: ');

	// Reserved
	blob.chk('000000000000', 'Reserved: ');
}