// of the unit tests.
	//
	// `s` gives the decrypted part sizes, and the other
	// parameters describe the desired read segment. When
	// `isFromEnd` is true, `skipLen` argument is ignored.
	decryptedRangeRef := func(s []int64, skipLen, readLen int64, isFromEnd bool) (o, l, skip int64, sn uint32, ps int) {
		oSize := lsum(s)
		if isFromEnd {
			skipLen = oSize - readLen
		}