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
		}
		if skipLen < 0 || readLen < 0 || oSize < 0 || skipLen+readLen > oSize {
			t.Fatalf("Impossible read specified: %d %d %d", skipLen, readLen, oSize)
		}

		var cumulativeSum, cumulativeEncSum int64
		toRead := readLen
		readStart := false